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Parts of the Scalp: A Guide to the Anatomy, Mechanics, and New Treatment Possibilities

If you’re experiencing hair loss, and you’re searching for a solution to help regrow hair, you’ve likely read several articles that reference different parts of the scalp. But what would you say if you were asked where on your scalp you’re losing hair? And how well do you understand the various parts of the scalp that lay beneath the skin, as well as their roles in hair loss?

In this article, we’ll give a quick introduction to the scalp. After that, we’ll take a tour of the scalp, starting with the different regions on the surface; then moving beneath the skin through the various layers of scalp tissue; then exploring the bones that lay beneath the tissue; then discussing the arteries, veins, nerves, and lymph vessels than run through those layers of tissue; and then examining the muscles that pull on the scalp. After touring the different areas of the scalp, we’ll discuss some ways that scalp mechanics may impact hair growth. Finally, we’ll look at some clinical evidence that has opened up the possibility of new treatments for androgenic alopecia. 

Introduction to the Scalp

The scalp consists of layers of skin and subcutaneous tissue that cover the human cranium. It extends from the supraorbital foramina (i.e. two openings in the bone just above the eye sockets and just beneath the eyebrows) to the superior nuchal line (i.e. one of four curved ridges on the exterior surface of the occipital bone, which lies at the back of the head). It is bordered on the front by the face and on the sides and back by the neck. 

The scalp acts as a physical barrier to protect the cranium against physical trauma and potential pathogens. It is also the area where human hair typically grows in order to 1) aid in heat conservation, and 2) play a role in aesthetic appearance and sexual signaling.   

A Tour of Your Head: Regions of the Scalp

If someone were to ask you where on your scalp you’re losing hair, would you know how to answer them? If you’re unsure how to answer that question, check out the descriptions below.

men hair shedding illustration

The surface of your head has seven main areas, or regions, which are described below:

  • Temples: The temples are located on either side of the head, behind the eye and between the forehead and ear. Each of the two temples is a latch where four skull bones – the frontal, parietal, temporal, and sphenoid bones – fuse together. Male pattern baldness typically starts at the temples, then continues to recede into the scalp, resulting in an M-shaped hairline. 
  • Frontal Region: If you were to draw an imaginary vertical line through your head, with the line positioned just in front of your ears, that line would demarcate the border between the frontal and mid-scalp regions. The part of the scalp that lies in front of that line is the frontal region. Also called the forelock, this region includes the hairline and the hair above the temples. If you’re losing hair due to male pattern baldness, this is often one of the first places you can expect to see hair loss. 
  • Mid-Scalp Region: If you were to draw two imaginary vertical lines through your head, with the first line positioned just in front of your ears and the second line positioned just behind them, the relatively flat area between those two lines would be the mid-scalp region. Unless you’re at an advanced stage of male pattern baldness, you probably won’t experience much hair loss in the mid-scalp region.  
  • Vertex Transition Zone: Also called the vertex transition point, this area is located between the mid-scalp region and the vertex. The vertex transition zone is the area where the scalp goes from a horizontal to a vertical plane posteriorly. For this reason, it is often referred to as the posterior hairline. Although this area is technically part of the vertex (see next bullet), it is often listed as a separate region. 
  • Vertex (Crown): Also called the crown, the vertex is the highest point on your scalp (the word “vertex” literally means “highest point”), which is located towards the back of your head. On non-balding heads, the vertex is typically identified by a swirl pattern of hair. In addition to losing hair around the temples and in the frontal region, many folks see noticeable hair loss on the crowns of their heads. 
  • Sides (Temporal Regions): Also known as the temporal regions (because they sit over the temporal bones and muscles), these are the areas on either side of the head that are positioned just above and behind the ears. Because the sides of the head have a different subcutaneous anatomy than the rest of the scalp, they are sometimes treated as separate from the scalp. However, the temporal regions generally grow hair, so we’ve chosen to include them in this tour of the scalp. Hair loss is much less common in this region. 
  • Back (Occipital Region): Also known as the occipital region (because it sits over the occipital bone and muscle), this area covers the back of the head, underneath the crown. As with the sides of the head, hair loss is much less common in this region. 

Digging into the Anatomy: Layers of the Scalp

While the previous section provides a good overview of the various areas on the surface of the scalp, there is a lot more going on beneath the surface.

Layers of scalp graphic
Tajran J, Gosman AA. Anatomy, Head and Neck, Scalp. [Updated 2021 Jul 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. 
The scalp consists of the following five layers:

  1. Skin: The first layer of the scalp is the skin, which acts as a protective barrier to the rest of the scalp, helps prevent the loss of moisture, and helps regulate body temperature, among other things. This layer is thick and contains numerous hair follicles and sebaceous glands (i.e. small, oil-producing glands).
  2. Dense Connective Tissue: The second layer is the dense connective tissue layer, which connects the skin to the galea aponeurotica (described below). In addition to connective tissue, this layer contains arteries, veins, nerves, and lymphatic vessels. Hair follicles can also extend from the skin down into this layer. 
  3. Galea Aponeurotica: Also known as the epicranial aponeurosis, the galea aponeurotica is a layer of dense, fibrous connective tissue that runs along the top of the cranium, connecting to the frontalis muscle at the front of the head and the occipitalis muscle at the back of the head.

The first three layers of the scalp are firmly attached to each other and move as a unified structure. 

  1. Loose Areolar Connective Tissue: This layer forms a flexible connection to both the galea aponeurotica and the pericranium (described below), allowing the top three layers of the scalp to slide over the lower pericranium. The loose areolar connective tissue also contains numerous blood vessels. 
  2. Pericranium: Composed of dense connective tissue, the pericranium is the deepest layer of the scalp, which tightly adheres to the calvaria (i.e. the bones that form the top of the skull). It also contains the vascular supply that’s essential to supporting the calvaria. 

The Scalp’s Foundation: The Calvaria and Other Cranial Bones

As noted above, the pericranium is firmly attached to the calvaria bones, which form the top of the human skull. In addition to the calvaria, there are some other cranial bones that play a role in scalp function. We discuss these bones below.

Skull graphic
Minonzio, Claudio. (2019). A step towards aberration corrections for transcranial ultrasound – Estimation of skull thickness and speed of sound.

The neurocranium, which is pictured in the image above, consists of the upper part of the skull that surrounds the cranial cavity and contains the brain. There are eight bones that make up the neurocranium:

  • The frontal bone forms a skeletal roof above the eye sockets and nasal cavity, and forms the main part of the forehead. 
  • The left and right parietal bones sit behind the frontal bone. These bones form the top and sides of the cranium.
  • The occipital bone forms the back and base of the skull. It has a large opening, called the foramen magnum, where the spinal cord passes into the skull.  
  • The left and right temporal bones help form the sides and base of the skull, where they protect the temporal lobe of the brain and surround the ear canal. 
  • The sphenoid bone is situated in the middle of the skull towards the front. It helps form the base and sides of the skull, and has a shape that resembles a butterfly. 
  • The ethmoid bone is a cube-shaped bone located in the center of the skull between the eyes. It helps form the walls of the eye sockets, as well as the roof, sides, and interior of the nasal cavity.

Although these are eight individual bones, they are joined together by various fibrous sutures.  

The neurocranium can be further divided into an upper and lower part:

  • The upper part, known as the calvaria, consists of the flat bones of the skull that form a dome-like roof. This includes the frontal bone, parietal bones, and occipital bone.
  • The lower part, known as the cranial base, includes the lower parts of the frontal bone, the sphenoid bone, ethmoid bone, temporal bones, and the lower parts of the occipital bone. 

Because the calvaria makes up the top part of the skull, these bones are more significant when discussing hair growth/loss. However, the muscles that attach to the temporal and sphenoid bones may also play a role in hair loss (more on that in a bit).

The Vertical Layer: Arteries, Veins, Nerves, and Lymphatic Vessels

We previously discussed the five layers of the scalp. There are also a number of arteries, veins, nerves, and lymphatic vessels that run through those layers. We discuss each of these below.

Arteries of the Scalp

The common carotid arteries, a pair of arteries on either side of the neck, provide the main supply of blood to the scalp. While still in the neck, each of the common carotid arteries splits into an internal and external carotid artery. Each of these branches supplies blood to different areas of the scalp. 

Internal Carotid Artery

Ophthalmic artery graphic
Wikipedia contributors. Ophthalmic artery. Wikipedia, The Free Encyclopedia. January 5, 2022, 11:55 UTC.

The internal carotid artery (on either side of the skull) gives rise to an ophthalmic artery, which further branches into a supratrochlear artery and a supraorbital artery. Both the supratrochlear and supraorbital arteries rise through the supraorbital foramen  (i.e. an opening in the bone just above the eye socket and just beneath the eyebrow) and connect with their counterparts on the opposite side of the skull, as well as with the superficial temporal artery (also on either side of the skull), which provides most of the blood supply to the front of the scalp. 

External Carotid Artery

Blood vessels on scalp
Hacking, C., Bell, D. Scalp. Reference article, Radiopaedia.org. (accessed on 12 May 2022)

The external carotid artery (on either side of the skull) branches into the following arteries:

  • The superficial temporal artery passes over the back of the cheekbone, where it splits again into a frontal and parietal branch. The frontal branch runs across the temple, supplying blood to the frontal and temporal regions of the scalp. The parietal branch continues over the top of the skull, supplying blood to the parietal region of the scalp. 
  • The posterior auricular artery splits away from the external carotid artery just above/behind the jaw and just below the ear. The posterior auricular artery then passes underneath the ear and travels to the deep tissues that converge between the mastoid process (i.e. the protruding, cone-shaped bone found just below and behind the ears on either side of the head) and the cartilage of the ear. This artery supplies blood to the parts of the scalp located above and behind the ears. 
  • The occipital artery splits from the external carotid artery at the back of the neck, passing under the ear and in front of the mastoid process. This artery supplies blood to the back of the scalp. 

Veins of the Scalp

The venous drainage of the scalp can be split into superficial and deep components.

Superficial Veins

veins in scalp graphic
Tajran J, Gosman AA. Anatomy, Head and Neck, Scalp. 2021 Jul 26. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan–. PMID: 31855392.
The superficial veins follow their respective arteries. The supraorbital and supratrochlear veins (on either side of the skull) drain blood from the top of the scalp through the front of the face, while the superficial temporal, occipital, and posterior auricular veins (also on either side of the skull) drain blood from the scalp through the back of the head. Also, just like its arterial counterparts, the superficial temporal vein has a frontal and parietal branch. 

Deep Veins

Deep veins on human
Rivard AB, Kortz MW, Burns B. Anatomy, Head and Neck, Internal Jugular Vein. 2021 Jul 26. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan–. PMID: 30020630.
The deeper regions of the scalp drain into the pterygoid venous plexus (on either side of the skull), which is a large plexus (i.e. a bundle of intersecting blood vessels, nerves, or lymphatic vessels) of veins situated between the temporalis (i.e. thin, fan-shaped muscles on either side of the skull) and lateral pterygoid (i.e. one of the muscles in the jaw that helps us chew) muscles. From there, the venous blood passes into the maxillary vein (on either side of the skull), then into the retromandibular vein (on either side of the skull), and then into the external jugular vein (on either side of the skull), which is the venous counterpart to the external carotid artery. 

The Connection Between Superficial and Deep Veins

veins in skull anatomy photo
Germann AM, Jamal Z, Al Khalili Y. Anatomy, Head and Neck, Scalp Veins. 2021 Dec 15. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan–. PMID: 31082005.
It’s also worth noting that there is a drainage connection between the superficial and deep venous systems, whereby parietal emissary veins located in the loose areolar connective tissue layer of the scalp connect to diploic veins that penetrate the skull, eventually flowing into the dural venous sinuses (e.g. superior sagittal sinus) that drain venous blood from inside the cranial cavity. 

Nerves of the Scalp

The front and sides of the scalp are innervated by trigeminal nerves, while the back of the scalp is innervated by cervical nerves.

Trigeminal Nerves

Nerves on head graphic
Wikipedia contributors. Trigeminal nerve. Wikipedia, The Free Encyclopedia. March 31, 2022, 01:23 UTC.

There are two trigeminal nerves – one on each side of the skull. Each trigeminal nerve has three major branches:

  • The ophthalmic nerve branches into the frontal nerve, which eventually splits into the following two branches:
  • The supratrochlear nerve innervates the front, middle section of the forehead. 
  • The supraorbital nerve innervates a large portion of the scalp including the top and sides of the forehead, as well as the vertex. 
  • The maxillary nerve branches into the zygomaticotemporal nerve, which innervates the temple.
  • The mandibular nerve branches into the auriculotemporal nerve, which innervates the skin in front of and above the ear. 

Cervical Nerves

cervical nerves anatomy of head
Roesch ZK, Tadi P. Anatomy, Head and Neck, Neck. 2021 Jul 26. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan–. PMID: 31194453.
Cervical nerves emerge from the spinal cord to innervate the rest of the body. There are four cervical nerves that innervate the scalp:

  • The lesser occipital nerve (on either side of the skull) arises from the anterior ramus (i.e. front-facing branch) of the second cervical nerve and innervates the skin above and behind the ear. 
  • The greater occipital nerve (on either side of the skull) arises from the posterior ramus (i.e. rear-facing branch) of the second cervical nerve and innervates the skin at the upper back of the scalp. 
  • The great auricular nerve (on either side of the skull) arises from the anterior rami (i.e. front-facing branches) of the second and third cervical nerves and innervates the skin below and behind the ear. 
  • The occipital nerve (on either side of the skull) arises from the posterior ramus  (i.e. rear-facing branch) of the third cervical nerve and innervates the skin at the lower back of the scalp. 

The Scalp’s Lymphatic Vessels

veins on head
Rivard AB, Kortz MW, Burns B. Anatomy, Head and Neck, Internal Jugular Vein. 2021 Jul 26. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan–.
The lymphatic vessels of the scalp are located in the dense connective tissue layer and follow the venous drainage. In general, the front portions of the scalp drain lymphatic fluid through the parotid nodes (i.e. lymph nodes found in front of and just below each ear), which continue to drain through the submandibular lymph nodes (i.e. lymph nodes located just beneath the jaw bone) and deep cervical lymph nodes (i.e. lymph nodes located in the neck). 

The rear portions of the scalp drain lymphatic fluid through the posterior auricular lymph nodes (i.e. a small group of lymph nodes located just beneath the ear) and occipital lymph nodes (i.e. lymph nodes located at the back of the head, near the occipital bone). The posterior auricular lymph nodes drain the area of the scalp located directly behind the ear and flow into the occipital lymph nodes, while the occipital lymph nodes drain lymphatic fluid from the remaining regions in the back of the scalp.

Muscles that Act on the Scalp

There are a handful of muscles that act on the scalp.

Muscles on head graphic
Roesch ZK, Tadi P. Anatomy, Head and Neck, Neck. 2021 Jul 26. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan–. PMID: 31194453.
The largest and most important muscle in the scalp is the occipitofrontalis muscle. The occipitofrontalis muscle is actually two sections of muscle, known as bellies, that connect to the front and back of the galea aponeurotica. The frontalis belly connects to the galea aponeurotica at the front of the head and inserts into the superior orbicularis oculi (i.e. the muscle that closes the eyelids) near the eyebrow. The occipitalis belly connects to the galea aponeurotica at the back of the head and attaches to the superior nuchal line (i.e. one of four curved ridges on the exterior surface of the occipital bone) and mastoid processes (i.e. the protruding, cone-shaped bones found just below and behind the ears on either side of the head) at the bottom of the scalp. These muscles, or bellies, work in conjunction to pull the scalp back and elevate the eyebrows (the contraction of the frontalis belly creates wrinkles on the forehead). 

The auricular muscles are a group of muscles of the auricle (i.e. the visible portion of the ear). Although there are nine total auricular muscles on either side of the skull, six of those muscles are intrinsic muscles located deep within the skull, while the other three are extrinsic muscles that are located more superficially. It is the three extrinsic muscles that we’re concerned with for this article. 

  • The auricularis superior, the largest of the three extrinsic auricular muscles, is a thin, fan-shaped muscle located above the ear. It helps to elevate the ear, attaching to the galea aponeurotica at the top and a tendon just above the ear at the bottom.  
  • The auricularis anterior, the smallest of the three extrinsic auricular muscles, is a thin, fan-shaped muscle located in front of the ear. It helps draw the ear upward and forward, attaching to the lateral edge of the galea aponeurotica at one end and cartilage at the top, front of the ear at the other.
  • The auricularis posterior is a muscle located behind the ear. It helps pull the ear backward, attaching to the mastoid process (i.e. the protruding, cone-shaped bone found just below and behind the ears on either side of the head) at one end and the lower part of the cranial surface at the back of the ear at the other end. 

Although the auricular muscles play a minor role in fixing the position of the ear, they are considered vestigial in humans. Nevertheless, these muscles may play a role in restricting blood flow to the scalp (more on this in a bit). 

The temporoparietalis muscles are a pair of muscles located just above and in front of the auricularis superior muscles on either side of the head. These muscles lie over both the temporal and occipital bones, connecting to the fascia (i.e. a thin sheath of fibrous tissue enclosing a muscle or other organ) just above the ear on one end and the galea aponeurotica on the other. The temporoparietalis muscles help to fix the galea aponeurotic and elevate the ears. 

The temporalis muscles are broad, fan-shaped muscles located on either side of the head. These muscles cover most of the temporal bones and help produce movements of the mandible, or jawbone, when chewing. Although these muscles are more associated with the mandible than they are the scalp, the contraction of these muscles may restrict blood flow to the scalp, which could have an effect on hair growth/loss (more on this below).

Ways Scalp Mechanics May Impact Hair Growth

Now that you have a better understanding of scalp anatomy, we can examine ways that scalp mechanics may impact hair growth. In particular, the galea aponeurotica and the surrounding musculature may play a role in restricting blood flow (and oxygen) to the scalp. 

We know from previous studies that balding scalps tend to have 2.6 x less subcutaneous blood supply compared to non-badling controls. Moreover, several blood-pressure-lowering medications – such as minoxidil, diaoxide, and pinacidil – have been shown to improve androgenic alopecia – one of the world’s most common hair loss disorders. These findings implicate reduced blood supply as a potential contributor to pattern hair loss. And while it’s still debated just how much the reductions to blood flow are a cause or consequence of androgenic alopecia, there may be a therapeutic benefit to improving blood, oxygen, and nutrient levels to balding hair follicles. 

Below, we examine the impact of scalp musculature on arterial branches, as well as the impact of the galea aponeurotica and surrounding musculature on microcirculation (i.e. capillaries in the scalp).

The Impact of Musculature on Arterial Blood Flow

Dermatologists report that roughly 80% of men with androgenic alopecia tend to have “tight” scalps, suggesting that the muscles around the perimeter of the scalp have involuntarily contracted and are pinching the arterial branches, causing a reduction in blood supply. This is also supported by research measuring scalp hardness in balding versus non-balding men across a variety of scalp regions.[1]https://www.researchgate.net/publication/338624064_Androgenetic_alopecia_is_associated_with_increased_scalp_hardness

So, do the muscles surrounding the scalp perimeter and anchored to the galea aponeurotica have anything to do with these phenomena? Some evidence suggests yes.

As noted previously, the supraorbital and supratrochlear arteries are two of the three arterial branches that supply the majority of blood to the frontal region of the scalp. These arteries pass through the cranial bone at the eyebrows, run underneath the frontalis muscle, then pierce through the frontalis muscle before running upward toward the hair line. When the frontalis muscle flexes, this flexing can compress the supraorbital and supratrochlear arteries, restricting blood flow to the scalp.[2]https://academic.oup.com/asj/article-abstract/41/11/NP1599/6206455

In addition, the deep temporal artery resides between the cranium and the temporalis muscles. When these muscles contract, they can compress the deep temporal artery against the skull and constrict blood supply. 

Moreover, some branches of the auricularis anterior and posterior arteries weave between the auricular muscles and their supporting tendons. It is possible that the contraction of the auricular muscles may restrict blood flow in the same manner. 

Finally, while many of the scalp’s arteries reside in the fascia that overlies the scalp muscles, the contraction of the muscles underlying these arterial branches can still affect them. We know this because studies have shown that when the temporalis muscle contracts, the artery overlying it (the superficial temporal artery) constricts by 50%, thus leading to a ~75% decrease in blood supply in that arterial branch.[3]https://n.neurology.org/content/11/11/935

But that’s not the whole story.

The Impact of the Galea Aponeurotica on Microcirculation

Despite the possible restriction of arterial blood flow described in the previous section, it is generally believed that reductions to blood flow in androgenic alopecia are mainly due to the loss/restriction of the microcapillary networks (i.e., the small blood vessels supporting the hair follicles themselves), rather than reductions from the carotid arterial branches supporting those microcapillary networks.

The microcapillary networks may constrict or compress as a result of mechanical stretch across the galea aponeurotica (mediated by the contraction of the scalp’s perimeter muscles). Because the top of the scalp is a fixed area, stretching of the galea aponeurotica would generate compression of the underlying microcapillary networks supplying hair follicles. 

How Relevant Is Blood Flow to Androgenic Alopecia?

We see hypoxia (i.e. insufficient supply of oxygen) as a trigger of hair loss in mouse models, but is it relevant to humans with androgenic alopecia? Unfortunately, we still don’t know (since there are also reductions to blood supply resulting from the hair follicle miniaturization that follows each re-entry into the anagen stage of the hair cycle). 

Interestingly, there used to be a surgery called “scalp reduction,” where surgeons would place a balloon underneath the galea aponeurotica, slowly inflate it over a series of weeks, and then give patients a surgery to “remove” bald regions and pull the hair-bearing stretched skin over to create the appearance of a fuller head of hair. In the 1990s, these surgeries were quietly abandoned after surgeons started voicing concerns of accelerated hair loss in patients following the procedure. Was this accelerated hair loss caused by skin tension? Did this tension lead to microcapillary compression? We still don’t know the answers, but the questions certainly are interesting.   

Clinical Evidence Suggests Possible New Hair Loss Treatment Targets

Botox injected into a male's scalp for hair loss

Despite the lack of certainty regarding the impact of blood flow (and oxygen) on androgenic alopecia, the results from a number of Botox studies show that when the muscles surrounding the scalp are forcibly relaxed in patients with androgenic alopecia, hair growth/loss improves. 

Botulinum toxin, which is commonly referred to by the brand name Botox, is an injectable neuro modifier that’s used as a therapeutic treatment for many clinical and cosmetic concerns. Specifically, Botox is used to help relax muscles and reduce certain inflammatory signaling proteins. 

Over the last decade, there have been five clinical studies published on the hair-promoting effects of Botox on men with androgenic alopecia. Four of those studies tested intramuscular Botox injections (i.e. injections directly into the scalp’s perimeter muscles), while the fifth study tested intradermal Botox injections (i.e. injections directly into balding regions of the scalp). We examine the results from both types of studies below.

The Results of Studies Testing Intramuscular Botox Injections

Across the four studies testing intramuscular Botox injections, 75-80% of participants responded favorably (i.e. hair growth) with an average hair count increase of 18-21% after 6 to 10 months. Injections into the scalp perimeter muscles were done once every 4-6 months, with results becoming cosmetically significant after the second round of injections. 

In addition to testing the use of Botox injections on their own, one of the four studies also examined using Botox injections alongside oral finasteride (i.e. the active ingredient in Propecia). This combined therapeutic approach led to improved response rates and hair count increases that average nearly 35%. 

Researchers suspect that two mechanisms contributed to these results:

  • First, intramuscular Botox injections might relax involuntarily contracted muscles around the perimeter of the scalp. As noted previously, arterial branches run through those perimeter muscles in order to supply the scalp with blood. When perimeter muscles are contracted, they may pinch those arteries, restricting the supply of blood to the scalp. Researchers theorize that injecting those perimeter muscles with Botox helps to unclamp the pinched arterial branches, increasing the supply of blood (and oxygen). 
  • Second, by relaxing those perimeter muscles, researchers also speculate that Botox injections might help reduce tension across the top of the scalp, and in doing so, potentially reduce tension-mediated inflammation and/or lower dihydrotestosterone (DHT) in the scalp. 

Despite researcher’s suspicions, it’s important to note that these suggested mechanisms are only speculative at this point. We will need more data in order to corroborate these suspicions. 

The Results of the Study Testing Intradermal Botox Injections

In the one study that tested intradermal Botox injections, 60-80% of participants responded favorably (i.e. hair growth) with an average hair count increase of 5% after 6 months. Injections into balding regions were done every four weeks. 

Although this study’s response rate is similar to the intramuscular studies above, the hair count increases were much lower. It’s worth noting that these results might improve with higher-dose injections. This study used just 30 units of Botox, spread across the entire scalp. When another investigator increased the amount of Botox injected from 30 units to 100 units, and also doubled the frequency of injections, they observed more significant hair growth.[4]https://www.dovepress.com/getfile.php?fileID=73853  

While conducting the study of intradermal Botox injections, researchers also conducted a cell culture on human hair follicles. They found that Botox appears to decrease the expression of transforming growth factor beta 1 (TGFB-1), a signaling protein that acts as a negative regulator of the hair cycle. TGFB-1 also appears to be intimately tied to hair follicle miniaturization, causing researchers to speculate that intradermal Botox injections might be down regulating TGFB-1 in human hair follicle sites, and in doing so, allowing for hair loss improvements. 

It’s important to note that the reduction of TGFB-1 happens in a dose- and time-dependent manner. Given this fact, it makes sense that increasing both the volume and frequency of intradermal injections evokes a more robust improvement in hair count. 

As with the intramuscular studies above, it’s important to note that the suspected mechanism (i.e. the down regulating of TGFB-1) identified in the intradermal study is only speculative. In order to corroborate this suspicion, more data will need to be collected. 

How Reliable Are the Findings from the Botox Studies?

Although the results from the Botox studies look promising, the amount of evidence on Botox as a treatment for androgenic alopecia is still rather small. And while several research groups have found consistent results, these studies tend to score lower on the hierarchy of evidence. So, we should interpret those results with caution. 

There are at least three significant issues with the Botox studies:

  • The Botox Studies Had a Small Number of Participants: To date, fewer than 200 participants have tested Botox to treat androgenic alopecia (in a clinical, peer-reviewed setting). For comparison, thousands of participants have tested the use of finasteride for treating androgenic alopecia. 
  • None of the Botox Studies Used a Control Group: At this point, no Botox studies have used control groups (i.e. patients who receive a placebo treatment). Using placebo groups is important because they help researchers control for hair count improvements (and losses) due to seasonal hair shedding. 
  • None of the Botox Studies Assessed Hair Diameter: While the Botox studies assessed hair count, they did not examine changes to hair diameter. Androgenic alopecia progresses through the process of hair follicle miniaturization, and we can effectively stop androgenic alopecia by reversing this process. Because we don’t know whether Botox has an effect on hair follicle miniaturization, we also don’t know whether Botox is an effective long-term solution for androgenic alopecia. 

In addition to the above three issues, it’s also worth noting that 1) there are currently no established best practices for the use of Botox to treat androgenic alopecia, and 2) Botox treatment can be rather expensive, with intramuscular injections costing $2,400 to $4,000 per year and intradermal injections running $4,800 to $12,000 per year. 

This isn’t to say we should dismiss the evidence in favor of using Botox to treat androgenic alopecia. At the same time, it’s important not to jump to any conclusions regarding the efficacy of using Botox versus other treatment options. 

Final Thoughts

In this article, we’ve shown how the scalp has a rather complex anatomy – including seven regions on the surface of the scalp; five tissue layers; several bones that the scalp attaches to; a number of arteries, veins, nerves, and lymphatic vessels running through the scalp; and a collection of muscles that pull on the scalp. We’ve also discussed ways that scalp mechanics may impact hair growth, and reviewed five studies that suggest Botox injections may improve hair loss by relaxing the muscles around the perimeter of the scalp.   

Although the findings from Botox studies are still preliminary, they have opened up the possibility of new treatment targets for androgenic alopecia. Any relevant treatment targets would need to relax the muscles around the scalp so that 1) arterial branches can deliver an adequate supply of blood (and oxygen) to the scalp, and 2) tension in the galea aponeurotica doesn’t restrict blood flow in the microcapillary networks that feed hair follicles. 

In addition to the results from the Botox studies, there’s mechanistic research to suggest that skin tension in balding regions (generated from the contraction of muscles around the scalp) might have something to do with the arrival of dihydrotestosterone (DHT) and the balding process itself.[5]https://www.sciencedirect.com/science/article/pii/S0306987717310411

Finally, it’s worth noting that Botox injections are not the only way to relax the muscles around the scalp. Scalp massages may offer a viable, less-expensive method for treating androgenic alopecia that targets the same mechanisms as Botox injections. 

References

References
1 https://www.researchgate.net/publication/338624064_Androgenetic_alopecia_is_associated_with_increased_scalp_hardness
2 https://academic.oup.com/asj/article-abstract/41/11/NP1599/6206455
3 https://n.neurology.org/content/11/11/935
4 https://www.dovepress.com/getfile.php?fileID=73853
5 https://www.sciencedirect.com/science/article/pii/S0306987717310411

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    2 thoughts on “Parts of the Scalp: A Guide to the Anatomy, Mechanics, and New Treatment Possibilities”

    1. Particularly interesting that you mention the superficial temporal artery (you probably already know where I’m going with this); have you seen the video by Brian Dye on malocclusion (II) and pattern baldness? His hypothesis for the cause of hair loss is IMO flawed and outdated (as his field of education isn’t hair loss disorders), but what’s interesting are his observations about the relation between the jaw and the superficial temporal artery.

      I have read some theories regarding this, and if I understand them correctly (I’m simplifying), occlusion of the artery cause inflammation, which irrigates in the scalp. Due to this inflammation, androgen receptors become upregulated, causing DHT to miniaturize the follicles.

      You and your team are no doubt more updated on this than me, although I hope this is stirring up some new ideas.

      Cheers

      Reply
      • Thanks Benjamin! I haven’t seen Brian Dye’s video, but I’ve read his paper on malocclusion and AGA. I think there’s merit to some sort of anatomical component acting as a driver (or accelerator) of AGA, even if it doesn’t explain all AGA cases. The botox studies on intramuscular injections (in my opinion) are the most compelling evidence we have on this. But we need more results replication across larger numbers of participants. I hope Brian Dye makes more of an effort to flush out his hypothesis (for example, using radioactive dye to track blood flow differences in balding versus non-balding scalps in relation to the artery in question).

        Reply

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