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Note: This article is technical. If you’re new to hair loss research, it’s best to start here.
Do Any Hair Loss Theories Hold Water?
When it comes to explaining why men and women lose their hair, no theory has all the answers.
Some researchers say that DHT causes hair loss. That’s sort of right. But unfortunately, even the DHT theory cannot explain…
- …why men start thinning at the hairline and vertex
- …why women start thinning evenly across the scalp
- …why men usually don’t lose hair at the scalp sides
- …why women thin all over, even at the scalp sides
- …why DHT encourages body hair growth, but scalp hair loss (the DHT paradox)
And while alternative hair loss theories get us closer to the answers, they still have holes.
This article uncovers the leading theories to pattern hair loss. For each theory, we’ll cover:
- The Science
- The Shortcomings
Theory #1: DHT Theory Of Baldness
This is the theory of all hair loss theories. It’s touted by most doctors, surgeons, and researchers trying to quickly summarize why someone’s balding.
Dihydrotestosterone, or DHT, is a hormone that comes from testosterone.
DHT is higher in thinning regions of men’s scalps. As a result, many researchers say that DHT causes hair loss.
I first heard about DHT when I was diagnosed with pattern hair loss in 2007. Here’s how my doctor described the process:
For reasons not fully understood, hair loss begins when DHT starts accumulating in our scalps. Our hair follicles become sensitive to DHT, then begin shrinking. Over a series of hair cycles, DHT makes our hair thinner and wispier, until our hair becomes so thin that it disappears. The end result: pattern baldness.
Beyond my doctor’s summary, there are three findings which form the DHT-hair loss argument:
- DHT is higher in the scalps of men with thinning hair.
- If a man is castrated, his testosterone and DHT levels plummet forever. Men castrated before puberty (ie: before their DHT levels spike) never go bald later in life.
- Some men have a rare genetic condition where they the lack an enzyme which converts testosterone into DHT in the scalp. Men who have this condition never lose their hair.
That’s a very compelling case… Just look at the extremes. If we never make any DHT, we never go bald. And if DHT is too high in our scalps, we lose our hair.
So what’s wrong with this theory?
The DHT-Hair Loss Theory’s Shortcomings
The DHT-hair loss theory leaves at least four questions unanswered:
- If DHT is the problem, then what causes DHT levels to rise in the first place?
- Why do our follicles become “sensitive” to DHT?
- How does DHT actually shrink our follicles?
- Why do men lose their hair in a horseshoe pattern, while women thin all over?
Doctors have a one word answer for all these questions: “Genetics.”
Unfortunately, that’s not only unproven, it’s also misleading.
DHT is just one of many factors associated with hair loss. It’s just one of several hormonal factors. It’s also just one of several biomarkers of a balding scalp – the others being arterial calcification, fibrosis, collagen remodeling, restricted blood flow, and a decreased subcutaneous fat layer.
Even worse, the DHT-hair loss theory doesn’t address DHT’s biggest paradox…
DHT in body and facial tissue encourages hair growth. DHT in scalp tissue discourages hair growth. Why?
Another leading theory takes a stab at answering this.
Theory #2: Gravity Theory Of Baldness
Another theory is the Gravity Theory Of Baldness, which came about in an effort to answer the paradox of DHT:
Why does tissue DHT encourage body hair growth and simultaneously discourage scalp hair growth?
The theory’s answer is quite simple: gravity.
One symptom of a balding scalp is an eroded subcutaneous fat layer.
Subcutaneous fat is an insulating layer of fat. It’s found all over the body – including our scalps (on the sides, back, and top). At the tops of our scalps, the subcutaneous fat rests between the scalp skin and the galea (more on that later):
When we’re younger, our scalp’s subcutaneous fat is relatively equal on the sides and top of our scalp. But during pattern hair loss, the subcutaneous fat at the top of the scalp starts getting thinner and more eroded.
According to the theory, here’s why:
Our heads are upright for most of the day, creating chronic pressure against the hair follicles and our scalp’s subcutaneous fat layer.
At the start of puberty, men’s androgen levels surge (we get more testosterone and DHT).
The Gravity Theory Of Baldness states that downward force + high androgens kickstart the erosion of subcutaneous fat in the scalp.
For women, the theory states that high estrogen levels preserve the scalp’s subcutaneous fat layer – at least until menopause when estrogen levels plummet.
According to the theory, this is why men start balding into early adulthood, and why women typically don’t lose their hair until later in life.
How Does This Explain The DHT-Paradox?
Well, DHT encourages body hair growth while also encouraging scalp hair loss.
According to the Gravity Theory Of Baldness, DHT will only encourage hair loss if there is constant downward force at that skin site (aka: gravity).
So, the top of men’s heads is under constant gravitational force. But their beards and body hair aren’t under the same force, because they’re angled differently.
And that’s why men don’t go bald at the sides of the scalp or on their bodies or faces. Gravity’s force isn’t directly downward there, so the subcutaneous fat layer doesn’t erode in the presence of androgens like it does at the top of the scalp.
Summarizing The Theory Step-By-Step
Men’s scalps are protected against the downward forces of gravity until puberty, at which point testosterone levels increase and begin to erode the scalp’s subcutaneous fat layer. When this happens, our hair follicle’s subcutaneous “cushion” starts disappearing. The hair has to work harder to continue growing and survive.
Since androgens encourage hair growth in other parts of the body, our body responds to the decrease in the scalp’s subcutaneous fat by sending more androgens there – in the form of DHT.
DHT is supposed to encourage hair growth! But in an effort to encourage hair growth, DHT – a testosterone derivative – also erodes more of the scalp’s subcutaneous fat layer. The process continues until the subcutaneous fat layer nearly entirely dissipates, miniaturizing the hair follicle until it eventually turns dormant.
Gravity, according to the author, explains why men only bald at the top of the scalp, and why DHT encourages body hair growth and scalp hair loss simultaneously.
The Gravity-Androgen-Hair Loss Theory Shortcomings:
If this theory feels incomplete, it’s because it is.
Problem #1: the theory doesn’t actually explain the “pattern” of male pattern hair loss.
While the author explains why men lose hair at the top of the scalp, he doesn’t necessarily explain why the loss occurs in a pattern – or why men generally start thinning at the temples and vertex, then progresses from there.
Problem #2: the Gravity Theory doesn’t explain why men bald differently than women.
Males typically recede at the hairline and thin at the crown, but most women thin all over.
How does the Gravity Theory explain women’s even thinning at the top and sides of the scalp? Technically, any thinning on the scalp sides refute this theory, or at least give evidence of another mechanism.
Problem #3: like women, men can also lose hair at the sides of the scalp, not just at the top.
Men in advanced stages of hair loss typically lose hair on the sides and even parts of their sideburns.
According to the Gravity Theory, the subcutaneous tissue shouldn’t erode here because it’s not under the same chronic gravitational force. But in advanced stages, men and women definitely experience hair loss in these places.
Problem #4: If this theory were 100% true, we’d also expect DHT to exert the same hair loss effect on other parts of our body that stay upright as long and as often as our heads.
For example, our shoulders. By the logic of the gravity theory, men should never get hairy shoulders. Why? The shoulders are on the same horizontal plane as the tops of our scalps. Our shoulders stay upright just about as long as the tops of our scalps, which means they’re under about the same gravitational pressure.
And at puberty, we’d expect a surge in androgens and the degradation of subcutaneous fat tissue in our shoulders, which means we’d be hard pressed to find any guy who’s balding with hairy shoulders.
Except here is a balding guy with hairy shoulders:
Hairy shoulders are so common I could start naming friends of mine with them.
As such, the Gravity Theory offers an incomplete explanation as to why DHT encourages hair growth and hair loss depending on the tissue. It doesn’t explain female pattern hair loss. And while the Gravity Theory might explain the relationship between a scalp’s decreased subcutaneous fat, increased DHT, and hair loss, it doesn’t come close to explaining the actual “pattern” of male pattern hair loss – or why recession and thinning starts at the temples and vertex.
The next theory does.
Theory #3: The Skull Expansion Theory
The third theory that offers an alternative explanation to the “pattern” of male pattern hair loss is The Skull Expansion Theory.
The theory is as follows: we know that the bones of the human skull continue growing throughout adulthood. We also know – based on observations – that balding men typically have a different head shape than non-balding men. Their forehead has a bulge at the midline, and some would even say their entire heads are larger than the heads of those unaffected by hair loss.
It turns out that DHT – which is elevated in balding scalp tissues – is also a hormone used by the body for bone remodeling.
The Skull Expansion Theory argues, like the Gravity Theory, that the presence of DHT should encourage hair growth, not hair loss. But because DHT also encourages bone growth, then elevated DHT in the scalp also increases skull bone growth. This bone growth expands the size of the skull, and in doing so, moves the follicles further away from the capillary networks that supports them. The resulting reduction of blood flow leads to follicle miniaturization, and subsequently, hair loss.
This theory is versatile in that it explains all the different patterns of hair loss for men. Skull bone growth at the front of the scalp leads to thinning at the temples. Skull bone growth at the back of the scalp leads to thinning at the vertex. If you take a walk around town, you can see for yourself the evidence of the skull expansion theory. Men who are receding at the temples typically have a bulge at the front of their scalp. If you’re suffering from pattern hair loss and you have older photos of yourself, you might even notice the development of this bulge as you began to thin over the years.
The Skull Expansion Theory Shortcomings
The first problem with the Skull Expansion Theory is that there are some men who clearly have experienced skull expansion, but also minimal or no hair loss. This is evident when we look specific cases of frontal bossing — or when the brow line begins to protrude far beyond the forehead.
Not all people with frontal bossing or forehead protrusion experience hair loss.
Moreover, frontal bossing and severe forms of skull expansion are often the result of excessive growth hormone release – sometimes due to a tumor in the pituitary gland. In some cases, the release can be so excessive and so chronic that a person’s hands, feet, face, head, and body continue to grow throughout adulthood.
This is called Acromegaly. Andre The Giant had the condition, but despite his bone growth, he also had pretty good hair.
So did this guy:
There are also cases of men whose skulls haven’t expanded much but have still gone bald.
His scalp is very well rounded – there’s no frontal bossing, and minimal (if any) expansion on the sides of his scalp. It looks as if he just shaved his head. He did. But during that period, he also lost a lot of hair.
The second problem is that the Skull Expansion Theory, like the Gravity Theory, doesn’t fully explain the difference in male versus female pattern hair loss, or why women typically thin evenly everywhere while men thin at the temples and vertex first.
With that said, I believe in the association between a bigger head and a balding scalp. Skull expansion is definitely a factor in many pattern hair loss cases. The theory deserves more attention and more research, and its author, Paul Taylor, deserves significant recognition for putting out an idea with more merit than, in my opinion, nearly every other theory. But as far as the skull expansion causing hair loss — I think this has still yet to be proven.
Which brings us to the last and most specific theory of all.
Theory #4: Muscular Tension / Tight Galea Theory
There are a few iterations of the tight galea and muscular tension theories of pattern hair loss, and I believe these theories – while still incomplete – take us closer than any other in addressing all the studied conditions of a balding scalp.
Each of those articles is worth your time. In fact, those findings are why I recommend spending so much time massaging the sides, nape, and sutures of your scalp – and not just your thinning areas.
The theory is as follows: the parts of the scalp predominantly affected by male pattern baldness are all above the galea. The galea is a fibrous tissue that rests over the entire top of the scalp. It’s a connective tissue that links the muscles above your eyebrow (frontalis) and the muscles behind your ears (occipitalis). There are no muscles on the top of your scalp – just the tendon-like fibrous tissue known as the galea.
For men, the areas of the galea aren’t really affected by hair loss. It’s just the hair residing over the galea that tends to disappear. So the question is, why?
It turns out that balding scalp tissue actually fuses to the galea.
Above our skull bones, our scalp has five tissue layers – the skin, the subcutaneous fat, the galea, the subgalea, and the pericranium. Again, here’s a reference:
In balding sites, the top three layers fuse together – the skin, subcutaneous fat, and the galea – creating one large, inseparable, fibrotic-ridden unit.
It’s important to note this fusing is unique to balding sites. It doesn’t happen in non-balding areas or at the hair sites on the sides or backs of our heads.
This fusing results in an increased presence of fibrotic tissue, a decrease in scalp skin elasticity, a decrease in the density of the scalp’s subcutaneous fat, and finally, hair loss.
But here’s the question no one’s yet figured out:
What causes the galea to fuse to the top two layers of our scalps?
There are a few different ideas:
Galea Fusion Theory #1
One idea is that androgens drive greater muscular development, and due to higher androgen levels, men tend to have larger developed muscles surrounding the galea. These muscles are difficult to fully relax. As a result, the muscles are often in contraction and chronically “pulling” on the galea, thereby tightening it.
A galea pulled tight by chronically contracted muscles restricts blood flow to the galea, and in doing so, reduces nutrient flow and oxygen levels of tissues supporting the hair follicles. Over sustained periods, a reduction in tissue oxygen levels can result in chronic low-grade inflammation, which eventually culminates into the development of fibrotic tissue – the same tissue that fuses together the top three layers of the scalp.
Interestingly, the areas where scalp tension is greatest are the vertex and the temples, meaning these areas should be the first to suffer from hypoxia, and the first to go bald.
This idea has existed for years and was partially validated by a study about Botox and hair loss – where Botox was injected at the scalp’s side and back muscles surrounding the galea to disable their movement. The six month results were a reduction in muscle size, a more relaxed galea, modest hair thickening, and partial hair regrowth.
This idea makes sense for men, but it doesn’t explain the different patterns in male versus female pattern hair baldness.
Galea Fusion Theory #2
We’re back to the Skull Expansion Theory. Androgens increase at puberty and drive, among other things, bone growth. For the most part, our skull bones continue developing throughout our adult lives – and part of this skull bone growth is mediated by DHT. As the skull bones grow, they increase the tension against the galea and its surrounding muscles, which restricts blood flow and reduces oxygen tissue levels (also known as hypoxia), which causes chronic inflammation that eventually culminates in fibrotic fusing of the skin, subcutaneous fat, and galea.
The same shortcomings as before. This theory gets us very close, but there are still cases of skull expansion without hair loss and little to no skull expansion with hair loss that challenge its completeness. This theory also doesn’t explain the difference in male versus female pattern hair loss – why women thin all over and men thin in a horseshoe-shaped pattern.
Galea Fusion Theory #3
The final idea is that the galea fuses with the scalp’s top two layers because of an increase in scalp androgen sensitivity mediated through mechanical force. This one is a mouthful, so bear with me.
We know that androgens, like DHT, play a role in pattern hair loss because men who are castrated before puberty have very low levels of DHT and don’t go bald later in life. We also know that tissue DHT levels are higher in balding versus non-balding parts of the scalp. This is why people associate DHT with hair loss. There’s definitely a relationship, but whether DHT is the cause of hair loss is still debated (as evidenced above). In any case, this phenomenon begs the question: why do tissue DHT levels increase only in balding areas, and not everywhere in the scalp?
Some researchers believe DHT levels are higher in balding regions because of an idea known as “enhanced androgen sensitivity.” And here comes the mouthful.
In order for DHT to accumulate in the scalp, DHT needs to attach itself to a receptor site. These receptor sites are known as androgen receptors.
Androgen receptors are located inside our cells. When DHT attaches to a cell’s androgen receptor, that DHT molecule will influence that cell’s functionality. For example, in certain facial and body tissue cells, DHT appears to influence cell function by encouraging hair growth. But for cells surrounding the hair above the galea, DHT appears to encourage hair loss.
How can that be? How can the same hormone encourage both hair growth and hair loss, with the only difference being body location?
It turns out that DHT molecules aren’t the only thing that influences a cell’s function. Certain proteins can also change cell behavior. These proteins are called androgen receptor “coactivators.” These coactivators interact with androgen receptors – the place where DHT binds – and “enhance” the androgen receptor’s function. In other words, these protein “coactivators” increase a cell’s sensitivity to androgens.
One of these coactivators is called Hic-5 / ARA55. This coactivator is highly active in beard tissues and in balding tissues of the scalp, but not so active in non-balding parts of the scalp like the back of the head.
This is important. In tissues with elevated DHT (the tissues that grow facial hair and the tissues in bald parts of the scalp), this protein coactivator is also higher. Some research suggests that this very coactivator regulates androgen sensitivity in human hair follicles. To put it bluntly, if a cell expresses the Hic-5 / ARA55 coactivator, you can bet that DHT will bind to it.
According to the theory, this is why some tissues accumulate DHT and others don’t. At puberty, the Hic-5 / ARA55 coactivator increases in facial, body, and scalp tissues above the galea. As a result, more DHT binds to those cells’ androgen receptors. Paradoxically, in the scalp, more DHT leads to hair loss. In the face and body, more DHT leads to hair growth.
But why? If an increase in Hic-5 / ARA55 explains why certain tissues start accumulating more DHT, then why does an increase in DHT cause hair loss at the scalp but hair growth in the body?
This is where the mechanical force element comes in.
It also turns out that increased DHT in the scalp also stimulates something called transforming growth factor beta 1 (TFG-β1). TFG-β1 is a signaling protein, and when it’s overexpressed, it leads to perifollicular fibrosis – or scarring surrounding the hair shaft that miniaturizes the hair and leads to hair loss. Chronically elevated levels of TFG-β1 are suspected to cause the fibrotic fusing we observe in the top three layers of balding scalps.
This creates the “perfect storm” hair loss cycle. It goes something like this:
- At puberty, an increase in androgens stimulates the expression of Hic-5 / ARA55 coactivators in body, facial, and certain scalp sites. This coactivator makes a cell’s androgen receptor more “sensitive” to DHT – and thereby more likely for DHT to bind to it.
- More DHT binds to androgen receptors in body, facial, and scalp tissues… But in the scalp tissues, more DHT also leads to an overexpression of TFG-β1.
- Above the galea, the overexpression of TFG-β1 results in perifollicular fibrosis. The hair follicles begin to miniaturize, and over time, this fibrosis begins to fuse together the top three layers of the scalp – the skin, the subcutaneous fat, and the galea.
- This “fusion” creates more mechanical tension, especially at the the vertex and temples, and that tension encourages an even higher expression of the Hic-5 / ARA55 coactivator.
- The Hic-5 / ARA55 coactivator encourages more DHT to the scalp tissue (increased androgen sensitivity), which increases TFG-β1, which increases perifollicular fibrosis, and then fibrotic fusion of the top three scalp layers (mechanical tension), which activates more Hic-5 / ARA55…
- …and the cycle repeats.
The more Hic-5 / ARA55, the more DHT, the more TFG-β1, the more perifollicular fibrosis, the greater the galea fibrotic fusion, and the more hair you lose… until the entire galea is fused with the top three scalp tissue layers.
This theory is the most complicated, and thereby lends itself to serious nitpicking. I won’t get into all of the issues, but these three shortcomings alone warrant more research:
- The theory’s argument that TFG-β1 increases more in the scalp than other body sites is unfounded. TFG-β1 is a signaling protein. It’s used in tissues all over the body for processes ranging from inflammatory responses to cell proliferation. While there’s evidence to suggest TFG-β1 inhibits hair growth, I’ve never seen anything that says TFG-β1 is higher in balding scalps than body or facial tissues that bear hair. That needs to be true for the theory to hold. But for now, this statement is just conjecture.
- The theory doesn’t explain why, at puberty, androgens stimulate the expression of Hic-5 / ARA55 in soon-to-be hair bearing body and facial tissues, on scalp tissue above the galea where hair is already present, but not on hair-bearing sites on the sides of the scalp. The theory says this coactivator over-expresses above the galea because of the mechanical tension already naturally occurring in the galea… But if this is the reason why the coactivator expresses itself above the galea but not on the sides of the head, then is there also similar tension at every other hair site on the body and face? Here we have a chicken-and-egg problem. Which came first: the tension or the Hic-5 / ARA55 coactivator? And even ignoring this, the theory still doesn’t explain the mechanism behind which androgens activate the Hic-5 / ARA55 coactivator. Basically, the theory consists of a lot of unproven assumptions.
- This theory doesn’t explain the different patterns in male and female pattern hair loss!
Problems with the Muscular Tension / Tight Galea Theory
Again, these theories don’t explain the different balding patterns in men versus women. They only explain pattern hair loss for men.
In fact, I haven’t come across an alternative or mainstream theory that addresses these differences. It’s a question we’ve yet to answer.
Otherwise, I tend to agree with the scalp tension and galea theories of hair loss more than others. Scalp tightness and chronic muscular tension can lead to the chronic inflammation that results in the calcification-fibrosis cascade of hair loss.
Which Hair Loss Theory Do I Believe?
I don’t adhere to any specific theory.
I think the Gravity Theory, Skull Expansion Theory, and Muscular Tension / Tight Galea Theory all have their flaws and merits. Each theory is capable of explaining most, but not all, of the pattern in the context of male pattern hair loss’ symptoms.
With that said, here’s what all these theories miss:
- None do a perfect job at explaining why women bald in a different pattern than men.
- None of these theories accurately address the DHT paradox – why DHT encourages body and facial hair growth but discourages scalp hair growth.
- None of these theories truly take into account the relationship between increased DHT, androgen receptors, imbalanced calcification regulators, and the very strong evidence that calcification and fibrosis precede hair loss by choking the follicles of proper blood, oxygen, and nutrient supply.
What can we glean from all of this?
We need to do more research.
If hair loss research orient their studies to answer…
- Why men bald differently than women
- Why DHT encourages body hair growth, and scalp hair loss
- Why, in advanced stages of androgenic alopecia, men lose hair at the sides and napes of the neck
…then I think those answers will take us closer to a universal cure.
Until then, I believe the best (and safest) hair loss solutions are to target calcification and fibrosis.
Rob English is a researcher, medical editor, and the founder of perfecthairhealth.com. He acts as a peer reviewer for scholarly journals and has published two peer-reviewed papers on androgenic alopecia. He writes regularly about the science behind hair loss (and hair growth). Feel free to browse his long-form articles and publications throughout this site.