Men lose hair primarily because of genetics and hormones. A hormone called DHT (dihydrotestosterone) shrinks hair follicles over time, gradually producing thinner, shorter strands until the follicle stops producing visible hair altogether. By age 35, about two-thirds of men will notice some degree of hair loss, and by 50, roughly 85% will have significantly thinning hair.
But genetics aren’t the only factor. Stress, nutritional deficiencies, thyroid problems, and scalp inflammation all play roles in how much hair you lose and how fast. Here’s what’s actually happening beneath the surface.
How DHT Shrinks Your Hair Follicles
Every hair on your head grows in cycles. The active growth phase lasts two to six years, followed by a short transition period, and then a resting phase where the hair eventually falls out and a new one begins growing. This is normal. You lose about 50 to 100 hairs a day as part of this cycle.
The problem starts with testosterone. Your body converts some testosterone into DHT using an enzyme called 5-alpha reductase. DHT binds to receptors on hair follicles, particularly the ones on top of your head and around your temples. Once DHT attaches, it triggers a process called miniaturization: the follicle gradually shrinks with each growth cycle. The active growth phase gets shorter, the hair it produces gets finer and lighter, and eventually the follicle becomes so small it can’t produce a visible strand at all.
This is why balding follows a predictable pattern. The follicles on the sides and back of your head have receptors that are largely resistant to DHT, which is why that horseshoe-shaped ring of hair tends to survive even in advanced baldness.
The Genetics Behind Pattern Baldness
You’ve probably heard that baldness comes from your mother’s side. There’s a kernel of truth here, but the full picture is more complicated. The gene most clearly linked to male pattern baldness is the AR gene, which sits on the X chromosome (the one you inherit from your mother). This gene provides instructions for building androgen receptors, the docking stations where DHT attaches to your follicles. Variations in the AR gene can make those receptors more sensitive to DHT, accelerating hair loss.
However, the AR gene isn’t the whole story. Researchers suspect that variants in several other genes contribute, and the condition clearly clusters in families on both sides. Having a close relative with pattern hair loss, whether it’s your father, grandfather, or uncle, increases your risk. The inheritance pattern remains unclear because so many genetic and environmental factors interact. The old rule of “look at your mother’s father” is a useful clue, not a guarantee.
How Hair Loss Progresses Over Time
Male pattern baldness follows a roughly predictable path, mapped out by what’s called the Norwood scale. This seven-stage system is the standard classification doctors use to assess how far hair loss has advanced.
- Stages 1 and 2: Little to no significant loss. The hairline may recede slightly around the temples, forming what’s sometimes called a “mature hairline.” Many men settle here permanently and never progress further.
- Stage 3: The first signs of clinically significant balding. The temple recession deepens noticeably, and some men begin thinning at the crown.
- Stages 4 and 5: The thinning areas at the temples and crown expand and start to merge. A band of denser hair still separates the two zones but gets progressively narrower.
- Stages 6 and 7: The most advanced stages. Only a band of hair around the sides and back of the head remains, and even that hair may be fine and sparse.
Not every man who starts losing hair will reach stage 7. Some stabilize at stage 3 or 4 and stay there for decades. The speed of progression varies enormously. Men who begin losing hair in their early twenties tend to reach more advanced stages than those who start in their forties.
Stress-Related Hair Loss
Pattern baldness gets the most attention, but stress can trigger a different type of hair loss called telogen effluvium. After a major physical or emotional stressor (surgery, severe illness, a death in the family, rapid weight loss), up to 70% of your actively growing hairs can prematurely shift into the resting phase all at once. Two to three months after the triggering event, those hairs start falling out, sometimes in alarming quantities.
The good news is that telogen effluvium is usually temporary. Most acute episodes resolve within six months once the stressor is removed. The hair grows back on its own. The catch is that in men already experiencing pattern baldness, stress-related shedding can accelerate what was already happening, making the loss feel sudden and dramatic when it’s really two processes happening at once.
Nutritional Deficiencies That Thin Your Hair
Your follicles need a steady supply of certain nutrients to maintain their growth cycle. Iron is the most well-documented. When your ferritin level (the protein that stores iron in your body) drops below 30 ng/mL, it’s highly likely to contribute to hair loss. Even levels between 30 and 40 may be too low for optimal hair growth. The sweet spot for healthy hair is generally above 70 ng/mL.
Vitamin D also appears to play a role. Studies consistently find that people experiencing hair loss have lower vitamin D levels than those who aren’t, though specific thresholds are still debated. Zinc shows up in many hair growth supplements, but unless you have a documented deficiency, there’s insufficient evidence that supplementing it will help. The broader point is that hair loss from nutritional deficiencies looks different from pattern baldness: it tends to be diffuse, affecting the entire scalp rather than following the typical temple-and-crown pattern.
Thyroid Problems and Other Medical Causes
Both an overactive and underactive thyroid can cause hair loss in men. Thyroid hormones help regulate the hair growth cycle, and when they’re out of balance, follicles can stop producing new hair entirely. The shedding pattern resembles telogen effluvium: widespread thinning rather than the receding hairline of pattern baldness, with excessive hair coming out during washing or brushing.
Other medical conditions that can cause or worsen hair loss include autoimmune disorders like alopecia areata (which creates patchy bald spots), scalp infections, and certain medications. If your hair loss doesn’t follow the typical pattern, happens suddenly, or is accompanied by other symptoms like fatigue or weight changes, something beyond genetics may be driving it.
The Role of Scalp Inflammation
Research has found that miniaturized follicles (the shrinking ones affected by DHT) show significantly more inflammation than healthy terminal follicles. Immune cells cluster around the upper portion of affected follicles, and the degree of inflammation correlates with how quickly those follicles are dying off. This suggests that DHT doesn’t act alone. It kicks off a cycle where the shrinking follicle attracts an inflammatory response, which further damages the follicle and speeds up the miniaturization process.
This finding has practical implications. Keeping your scalp healthy through regular washing, managing conditions like dandruff or seborrheic dermatitis, and reducing oxidative stress may not prevent pattern baldness, but it can slow the inflammatory component that accelerates it.
What Treatment Looks Like Today
The two most established treatments for male hair loss work by targeting different parts of the problem. One approach blocks the enzyme that converts testosterone into DHT, reducing DHT levels throughout the body. The other stimulates blood flow to the scalp and extends the growth phase of existing follicles. Current expert consensus favors oral forms of both treatments as first-line options for men.
A long-term study following over 500 men taking a DHT-blocking medication for ten years found that 91.5% showed improvement and 99.1% at least prevented further progression. Those are unusually strong numbers for any medical treatment, though results vary by individual and tend to be best when treatment starts early, before follicles have fully shut down.
These treatments work best at maintaining what you have rather than regrowing what’s already gone. A follicle that has been miniaturized for years is much harder to revive than one that’s just beginning to shrink. This is why dermatologists consistently emphasize starting treatment at the first signs of thinning rather than waiting until loss is advanced. For men with significant hair loss who want restoration, surgical hair transplantation relocates DHT-resistant follicles from the back of the head to thinning areas, producing permanent results.