Men’s hair falls out primarily because of genetics. A hormone called DHT (dihydrotestosterone) shrinks hair follicles over time, producing thinner and shorter strands until the follicle stops growing hair altogether. This process, called male pattern baldness, affects roughly two-thirds of men by age 35 and about 85% by age 50. But genetics isn’t the only reason. Stress, nutritional deficiencies, autoimmune conditions, and scalp problems can all trigger hair loss in men too.
How DHT Shrinks Your Hair Follicles
Your body converts testosterone into DHT, a more potent hormone that binds to receptors on hair follicles. In men who are genetically susceptible, DHT activates those receptors and essentially tells the follicle to shrink. This process is called miniaturization. Over months and years, each affected follicle produces a thinner, shorter, lighter hair until it eventually stops producing visible hair at all.
DHT also shortens the growth phase of hair. Normally, a hair on your head grows actively for 2 to 8 years before entering a brief transition period of about 2 weeks, then resting for 2 to 3 months before falling out and being replaced. When DHT interferes, that growth phase gets progressively shorter. The hair doesn’t have time to reach its full length or thickness before it falls out, and eventually the follicle can’t produce a replacement.
This is why male pattern baldness follows such a predictable pattern. It typically starts with a receding hairline at the temples and thinning at the crown, because the follicles in those areas have more hormone receptors than the ones along the sides and back of your head. About 25% of men with this type of hair loss notice it before age 21.
The Norwood Scale: Recognizing Your Stage
Doctors classify male pattern baldness using the Norwood scale, which has seven stages. Stage 1 means no significant hair loss. Stage 2 shows slight recession at the temples. From there, the hairline continues to recede and the crown thins until, at stage 7, only a band of hair remains along the sides and back of the head. There’s also a less common variation called “class A,” where the hairline recedes uniformly from front to back without the typical island of hair in the middle and without a separate bald spot at the crown.
Knowing your stage matters because treatments work best in the earlier stages, when follicles are miniaturized but not yet dead. Once a follicle has been dormant long enough, it can’t be revived with medication.
Stress, Illness, and Temporary Shedding
Not all hair loss in men is permanent. Telogen effluvium is a type of widespread shedding triggered by a physical or emotional shock to the body. Instead of individual follicles miniaturizing over years, a large number of hairs are pushed into the resting phase all at once, then fall out two to three months later. The triggers include high fever, severe infections, major surgery, rapid weight loss, and intense psychological stress.
Restrictive diets are a particularly common culprit. Crash dieting or eating plans that lack adequate protein can push hair into the shedding phase. Certain medications can also trigger it, including some blood pressure drugs, antidepressants, and anti-inflammatory medications. The reassuring part: telogen effluvium is almost always reversible. Once the underlying trigger is resolved, hair typically regrows on its own within six to nine months.
Nutritional Deficiencies That Thin Your Hair
Three nutrients have strong evidence linking them to hair health: iron, vitamin D, and vitamin C (because it helps your body absorb iron). Iron deficiency is the most common nutritional cause of hair loss. Your body stores iron as ferritin, and while most labs flag ferritin levels below 15 to 30 ng/mL as low, dermatologists use a higher threshold. Levels below 30 ng/mL are highly likely to contribute to hair loss, and many hair specialists consider 70 ng/mL or above optimal for hair growth.
People experiencing hair loss also consistently show lower vitamin D levels than those without hair problems. If you’re losing hair and suspect a nutritional cause, a blood test for ferritin and vitamin D is the most useful starting point.
What about biotin, zinc, and all those “hair growth” supplements? Biotin deficiency does cause hair loss, but it’s extremely rare in anyone eating a normal diet. For zinc, B12, and folate, medical reviews consistently find insufficient evidence to recommend supplementation unless you have a documented deficiency. And some supplements can backfire: vitamin A and selenium both cause hair loss when taken in excess, so megadosing on a multivitamin can actually make things worse.
Autoimmune Hair Loss: Alopecia Areata
Alopecia areata looks very different from male pattern baldness. Instead of gradual thinning, it causes sudden, round or oval patches of bare skin, often on the scalp but sometimes in the beard area, eyebrows, or eyelashes. Around the edges of these patches, you may notice short broken hairs that are narrower at the base than the tip, sometimes called “exclamation point” hairs.
This happens because the immune system mistakenly attacks hair follicles. The genes involved are related to immune function, and people with other autoimmune conditions like thyroid disease, psoriasis, or vitiligo are more likely to develop it. Alopecia areata comes in different forms. The most common is patchy, with one or more coin-sized bald spots. In rarer cases, it can progress to total loss of scalp hair (alopecia totalis) or complete loss of body hair (alopecia universalis).
Scalp Conditions and Inflammation
Chronic scalp conditions like seborrheic dermatitis, the more severe form of dandruff, can cause noticeable hair shedding. The hair loss comes primarily from scratching inflamed, itchy areas rather than from direct damage to the follicle itself. This means it’s not permanent. Once the inflammation is treated and the scratching stops, hair in affected areas grows back normally.
Treatments That Slow or Reverse Loss
Two treatments have the longest track record for male pattern baldness. The first is a topical solution applied directly to the scalp, available over the counter in 2% and 5% concentrations. The 5% version produces about 45% more regrowth than the 2% version based on a 48-week comparison study. A low-dose oral form has also come into use, though it wasn’t originally designed for hair loss.
The second is a prescription pill that works by blocking the conversion of testosterone to DHT. A large Japanese study followed over 3,100 men and found that after 42 months, about 87% showed some degree of improvement: 11% had significant regrowth, 37% moderate regrowth, and 40% a slight increase in hair growth. Side effects occurred in less than 1% of participants. A separate 10-year follow-up found that the medication worked better in men over 30 and in those with more advanced hair loss at the start. One concern worth knowing about: a study found that sperm quality temporarily worsened at six months but returned to baseline by 12 to 24 months.
For alopecia areata specifically, newer medications that target the immune system’s signaling pathways have received FDA approval. However, early data shows that many patients discontinue within the first six months, suggesting that effectiveness or tolerability varies significantly from person to person.
The most important factor in treating any type of hair loss is identifying the cause correctly. Pattern baldness, stress-related shedding, nutritional deficiency, and autoimmune loss all require completely different approaches, and a treatment that works for one can be useless for another.