Male pattern baldness is the most common cause of hair loss in men, driven primarily by genetics and hormones. It affects about 1 in 5 men in their 20s, 1 in 3 in their 30s, and nearly half of all men over 40. But pattern baldness isn’t the only reason men lose hair. Stress, nutritional gaps, medications, scalp conditions, and autoimmune disorders can all play a role.
How Hormones Shrink Hair Follicles
The central player in male pattern baldness is dihydrotestosterone, or DHT. Your body converts a portion of testosterone into DHT using an enzyme called 5-alpha reductase. DHT itself isn’t harmful in most of the body, but hair follicles on the top and front of the scalp are uniquely sensitive to it. When DHT binds to receptors on those follicles, it triggers a process called miniaturization: the follicle gradually shrinks, produces thinner and shorter hairs with each growth cycle, and eventually stops producing visible hair altogether.
This is why men with pattern baldness still have hair on the sides and back of their heads. Those follicles lack the same sensitivity to DHT. The process is slow, typically unfolding over years or decades, which is why hair loss often feels gradual rather than sudden.
The Genetics Behind Pattern Baldness
Hair loss runs in families, but the inheritance pattern is more complicated than the old idea that you get it from your mother’s father. Early research suggested male pattern baldness followed a single-gene dominant inheritance pattern, but studies have found the reality is polygenic, meaning many genes across multiple chromosomes contribute to your risk. A strong resemblance between fathers and sons in baldness patterns supports a hereditary component, but it doesn’t follow a simple, predictable path.
What you inherit isn’t baldness itself but the sensitivity of your hair follicles to DHT. Two men can have identical testosterone and DHT levels, yet one loses his hair while the other keeps a full head of it. The difference comes down to how their follicles are genetically programmed to respond.
Stress and Sudden Shedding
If your hair loss came on quickly and seems to be thinning all over rather than receding at the temples, the cause may be telogen effluvium. This is a temporary form of hair loss triggered when a large number of follicles simultaneously shift from the growth phase into the resting phase, causing noticeable shedding roughly two to three months after the triggering event.
Common triggers include high fever, severe infections, major surgery, rapid weight loss, and significant psychological stress. Restrictive diets that lack adequate protein are another frequent culprit. Telogen effluvium looks and feels different from pattern baldness: instead of a receding hairline or thinning crown, you’ll notice more hair in the shower drain and on your pillow, with diffuse thinning across the entire scalp. The good news is that once the underlying stressor resolves, hair typically regrows on its own.
Nutritional Deficiencies That Thin Hair
Your hair follicles need a steady supply of specific nutrients to function. Iron is responsible for carrying oxygen to follicles so they can grow. Vitamin D plays a role in creating the cells that develop into hair follicles. Vitamin C helps your body absorb iron from food, so a deficiency in one can worsen the effects of the other.
There’s conflicting evidence on whether supplements like biotin, zinc, or selenium help with hair loss unless you actually have a confirmed deficiency. And more isn’t always better. Excessive intake of vitamin A and selenium can actually increase hair loss, and too much vitamin A or iron is toxic. If you suspect a nutritional gap is contributing to thinning hair, blood work to check your levels is far more useful than blindly taking supplements.
Medications That Cause Hair Loss
A surprisingly long list of common medications can trigger hair shedding as a side effect. The usual pattern mimics telogen effluvium: diffuse thinning that begins weeks to months after starting a new drug. Drug classes linked to hair loss include blood thinners, cholesterol-lowering medications, blood pressure drugs (including beta-blockers and diuretics), antidepressants, anti-seizure medications, acne treatments containing vitamin A derivatives, NSAIDs like ibuprofen, thyroid medications, mood stabilizers, and immunosuppressants.
Chemotherapy is the most dramatic example. These drugs target rapidly dividing cells, and hair follicle cells are among the fastest-dividing in the body, which is why hair loss during cancer treatment is so common and often so complete. Unlike most medication-related shedding, chemotherapy can cause hair to fall out within days or weeks rather than months.
Autoimmune Hair Loss
Alopecia areata is a different mechanism entirely. Instead of hormones or external triggers, the immune system itself attacks hair follicles. Certain immune cells surround the lower part of the hair bulb during the growth phase, collapsing the follicle’s natural immune protection and disrupting the growth cycle. The result is typically smooth, round patches of baldness on the scalp, though it can progress to total scalp hair loss or, in rare cases, loss of all body hair.
The onset and progression are unpredictable. Some people develop a single patch that regrows within months. Others experience recurring episodes. About 80% of people who develop alopecia areata for the first time see spontaneous regrowth within a year, but relapse can happen at any stage. Unlike pattern baldness, alopecia areata can strike at any age and doesn’t follow the typical receding hairline or crown thinning pattern.
Scalp Conditions and Inflammation
Chronic scalp inflammation can contribute to hair thinning even when your hormones and genetics aren’t working against you. Seborrheic dermatitis, a common condition that causes flaky, itchy, inflamed skin on the scalp, is one example. Excess oil production irritates the scalp and feeds an overgrowth of a naturally occurring yeast called Malassezia. The resulting inflammation damages follicles and disrupts normal hair growth.
Scratching an itchy scalp compounds the problem by physically damaging follicles. The hair loss from seborrheic dermatitis is generally reversible once the inflammation is controlled through antifungal and anti-inflammatory treatments. If you’re dealing with persistent flaking, redness, or itching alongside hair thinning, the scalp condition may be a contributing factor worth addressing on its own.
How to Tell Which Type You Have
The pattern of your hair loss is the most useful clue. A receding hairline that moves backward from the temples, thinning at the crown, or both, strongly suggest pattern baldness. Diffuse thinning across the entire scalp, especially if it started suddenly, points toward telogen effluvium, a nutritional issue, or a medication side effect. Smooth circular patches are the hallmark of alopecia areata. And if thinning is accompanied by an itchy, flaky scalp, inflammation may be playing a role.
Many men have more than one factor at play. Pattern baldness can overlap with stress-related shedding or a nutritional deficiency, making the hair loss worse or faster than genetics alone would explain. Identifying all the contributing causes, not just the most obvious one, is what leads to the most effective approach to slowing or reversing the loss.