Your Hair Loss Isn't Just Bad Luck. Your Genes Control DHT Sensitivity.

The androgen receptor is a protein that sits on the surface of your hair follicles and throughout your body. When DHT binds to this receptor, it triggers a cascade of changes inside the cell. In hair follicles, DHT signals the follicle to shrink and shorten its growth cycle, a process called miniaturization. In other tissues, DHT builds muscle, deepens your voice, and drives male pattern traits.

The AR gene has a variable section called a CAG repeat. The number of CAG repeats you inherit determines how sensitive your androgen receptor is. Fewer repeats mean a more sensitive receptor; more repeats mean a less sensitive one. If you inherit shorter CAG repeats from both parents, your androgen receptors are hyperresponsive. This means your hair follicles will shrink in response to even normal or low DHT levels. The effect is common and dose-dependent; the shorter the repeats, the faster the hair loss typically begins.

This is why two men with identical DHT levels can have completely different hair patterns. One might have a full head of hair at 50. The other might be bald by 35. The difference is CAG repeat length. If you have short repeats, DHT doesn’t have to be high to cause problems. Even a small amount will trigger miniaturization in your follicles.

The enzyme 5-alpha reductase type 2 converts testosterone into DHT. It’s the gatekeeper that controls how much DHT your body makes. If you have a variant that increases this enzyme’s activity, you’ll produce more DHT from the same amount of testosterone. If you have a variant that decreases activity, you’ll produce less.

The most common variant is V89L (rs523349), carried by roughly 30 to 40% of the population in European ancestry. Depending on which version you inherit, your 5-alpha reductase activity could be significantly higher or lower than average. If you have variants that boost this enzyme, your DHT production is naturally elevated, making hair loss more likely across all your hair-bearing areas. This isn’t about sensitivity; this is about volume. Your body is making too much of the hormone that shrinks follicles.

If you have this variant, you’ll likely notice early-onset hair loss, body hair growth that seems excessive for your age, or oily skin. Your DHT levels in bloodwork (if you’ve had them measured) probably came back elevated. Standard treatments that lower DHT are particularly effective for you because your problem is overproduction, not oversensitivity.

Estrogen is protective for hair. It extends the growth phase of the hair cycle and delays the transition to shedding. The estrogen receptor (ESR1) sits on hair follicles and other tissues, receiving the estrogen signal. When estrogen binds strongly, follicles stay in growth mode longer. When the signal is weak, follicles shed prematurely.

The ESR1 gene has common variants (PvuII and XbaI polymorphisms) that reduce how well the estrogen receptor responds to estrogen. Roughly 40% of the population carries these variants. If you have these variants, your hair follicles are less responsive to estrogen’s protective effects, even if your estrogen levels are normal. This is particularly significant for people assigned female at birth; estrogen is naturally higher, but if your receptors don’t listen to that signal, you won’t get the protective benefit. For people assigned male at birth, low estrogen plus poor receptor sensitivity compounds the problem.

You might notice this if you’ve experienced hair thinning after hormonal shifts, such as postpartum, during perimenopause, or after hormonal birth control changes. You might also notice it if your hair loss is diffuse (all over) rather than patterned, because the estrogen protection is failing broadly.

MTHFR is the enzyme that controls methylation, a fundamental cellular process that provides the methyl groups your cells need for DNA synthesis, repair, and energy production. Hair follicles are among the fastest-dividing cells in your body. They require enormous amounts of energy and raw materials to grow. If methylation is impaired, follicles starve.

The C677T variant in MTHFR, present in roughly 40% of people with European ancestry, reduces enzyme efficiency by 40 to 70%. If you carry this variant, your hair follicles don’t have enough methylation capacity to support rapid cell division and regeneration. This manifests as diffuse thinning rather than patterned loss, because it’s a global energy problem, not a DHT-sensitivity problem. Your hair might be finer, or you might notice hair shedding that’s more generalized and harder to pinpoint.

MTHFR variants also affect your ability to process B vitamins properly, which compounds the energy deficit. You might feel this in your whole body, not just your hair: fatigue, brain fog, or slow recovery from stress. The hair loss is just the most visible sign that your cells are energy-starved.

Vitamin D is a hormone that regulates hair follicle cycling. The vitamin D receptor (VDR) is the protein that receives the vitamin D signal and tells hair follicles when to enter growth phase, resting phase, or shedding phase. Without proper VDR signaling, follicles can’t activate their growth cycle properly. They become stuck in resting or telogen phase, leading to excessive shedding and sparse regrowth.

Common VDR variants (BsmI and FokI polymorphisms) are present in 30 to 50% of the population. If you carry these variants, your VDR is less responsive to vitamin D, so your hair follicles don’t receive the activation signal they need to grow, even if your vitamin D levels are technically normal. This is why some people with normal vitamin D bloodwork still experience hair loss; their receptors aren’t listening to the signal.

You might notice this as telogen effluvium, a pattern where hair sheds heavily but regrowth is sparse or delayed. You might also have experienced this triggered by stress, illness, or hormonal change, because VDR dysfunction makes follicles more vulnerable to these triggers.

Iron is essential for mitochondrial function. Hair follicles are energy-intensive; they need robust mitochondria to power rapid cell division. The HFE gene regulates how much iron your body absorbs and stores. If HFE variants disrupt this regulation, you can accumulate too much iron (hemochromatosis) or, more commonly in heterozygous carriers, struggle with iron balance that affects energy production.

HFE variants like C282Y and H63D are common, carried by roughly 10 to 20% of people with European ancestry in heterozygous form. People with HFE variants may have disrupted iron metabolism that impairs mitochondrial function in hair follicles, reducing the energy available for growth. This can interact with other factors; if you also have MTHFR or VDR issues, poor iron metabolism makes everything worse. The result is slow hair growth, diffuse thinning, or hair that sheds excessively because follicles lack energy to sustain the growth cycle.

You might also notice fatigue, brain fog, or difficulty recovering from exercise, because the mitochondrial dysfunction affects your whole body. Hair loss is just the first sign you notice because hair follicles are so energy-dependent.