Hair loss in men is overwhelmingly driven by genetics, but it’s not the only cause. Roughly 30% of men show signs of pattern baldness by age 30, 50% by age 50, and the numbers keep climbing with each decade. Understanding what’s behind your hair loss matters because the cause determines whether it’s reversible, treatable, or simply something to manage.
Male Pattern Baldness: The Most Common Cause
The vast majority of hair loss in men comes down to a combination of genetics, hormone levels, and aging. Your body converts testosterone into a more potent hormone called DHT, which gradually shrinks hair follicles on the top and front of your scalp. Over time, affected follicles produce thinner, shorter hairs until they stop producing visible hair altogether. The follicles on the sides and back of your head are naturally resistant to DHT, which is why those areas tend to keep their hair even in advanced baldness.
Contrary to the old belief that baldness comes from your mother’s side, genes from both parents contribute. If your father, maternal grandfather, or uncles lost their hair, your risk goes up, but there’s no single gene that seals your fate. The pattern typically follows a recognizable progression: a receding hairline at the temples that forms an M or V shape, thinning at the crown, and eventually a merging of the two areas. In the most advanced stage, only a band of hair around the sides and back of the head remains.
The incidence tracks almost perfectly with age. About 20% of men in their 20s have some degree of pattern baldness, 40% in their 40s, and by the 90s, roughly 90% are affected. If you’re noticing a gradually receding hairline or a widening part, pattern baldness is by far the most likely explanation.
Stress and Illness Can Trigger Sudden Shedding
If your hair loss came on suddenly and seems to be thinning all over rather than receding in a pattern, you may be dealing with a condition called telogen effluvium. This happens when a shock to your system pushes a large number of hair follicles into their resting phase at the same time. Two to three months later, those hairs fall out in clumps, often noticeably during showering or brushing.
Common triggers include high fever, severe infections, major surgery, significant psychological stress, and crash diets that lack enough protein. Thyroid problems, both overactive and underactive, can also push hair into this shedding phase. The thyroid gland controls your metabolism, and when its hormone output is off, your body deprioritizes hair growth. People with thyroid dysfunction often notice excessive shedding during washing, brushing, or styling.
The reassuring part: telogen effluvium is temporary. Once the underlying trigger resolves, shedding typically stops within three to six months, and new growth follows in the affected areas. If you can identify and address the cause, your hair should recover on its own.
Medications That Cause Hair Loss
A number of common medications can trigger hair shedding as a side effect. If your hair loss started within a few months of beginning a new prescription, the drug itself may be responsible. Classes of medication linked to hair loss include:
- Blood pressure medications: beta-blockers and ACE inhibitors
- Blood thinners: heparin and warfarin
- Antidepressants: SSRIs like fluoxetine and sertraline, as well as tricyclic antidepressants
- Cholesterol-lowering drugs
- Gout medication: colchicine
- Acne treatments: isotretinoin and other vitamin A-based drugs
- NSAIDs: over-the-counter pain relievers like naproxen
- Steroids and hormone therapies
Chemotherapy drugs are well known for causing rapid, widespread hair loss, but that’s a distinct mechanism where the drug actively targets fast-dividing cells, including hair follicles. Most other medications cause the slower telogen effluvium type of shedding. In either case, hair typically regrows after the medication is stopped or adjusted.
Nutritional Deficiencies and Hair Thinning
Your hair follicles are metabolically active and need a steady supply of nutrients. Iron is one of the most important, and the threshold for hair health is higher than many people realize. Standard lab results may flag your iron storage levels (ferritin) as “normal” at 15 to 30 ng/mL, but hair specialists consider levels below 30 highly likely to contribute to hair loss. The optimal range for hair growth is 70 ng/mL or above, with 40 to 70 considered the minimum for healthy hair.
Men who eat restrictive diets, have digestive conditions that impair nutrient absorption, or simply don’t eat enough protein are most at risk. Low vitamin D and zinc levels have also been linked to hair thinning, though iron deficiency is the most well-documented nutritional contributor. A simple blood test can identify whether a deficiency is playing a role, and correcting it through diet or supplementation often helps restore normal growth over several months.
Autoimmune Hair Loss: Alopecia Areata
Alopecia areata looks distinctly different from pattern baldness. Instead of a gradually receding hairline, it causes sudden, coin-sized bald patches that appear on the scalp, beard, eyebrows, or other body hair. The immune system mistakenly attacks hair follicles, causing inflammation that shuts down hair production in those spots. The patches are typically smooth, with no rash, redness, or scarring. Around the edges, you may notice short broken hairs that are narrower at the base than the tip, sometimes called “exclamation point” hairs.
Alopecia areata can affect men at any age and is unpredictable. Some people experience a single episode with full regrowth, while others have recurring patches. In rare cases, hair loss progresses to the entire scalp or body. Because it’s an autoimmune condition, it sometimes occurs alongside other immune-related conditions like thyroid disease or vitiligo.
Scalp Conditions That Interfere With Growth
Chronic scalp inflammation can contribute to hair shedding, though it rarely causes permanent loss on its own. Seborrheic dermatitis is one of the most common culprits. It’s driven by an overgrowth of a yeast that naturally lives on everyone’s skin. When the yeast population gets too large, it breaks down the oils on your scalp into fatty acids that irritate the skin, causing redness, itching, and flaking. The persistent scratching and inflammation can lead to hair shedding in affected areas, but the hair grows back once the condition is controlled.
Fungal infections, psoriasis, and folliculitis (infected hair follicles) can also cause localized hair loss. These are generally treatable, and hair recovery depends on how long the inflammation has been active. Prolonged, untreated inflammation can sometimes damage follicles enough to cause scarring, which makes hair loss in those spots permanent.
How to Tell What’s Causing Your Hair Loss
The pattern and speed of your hair loss are the most useful clues. A slowly receding hairline or thinning crown that’s been progressing over months or years almost certainly points to genetic pattern baldness. Sudden, diffuse shedding all over your scalp suggests telogen effluvium from stress, illness, or medication. Distinct round patches with smooth skin point toward alopecia areata.
Consider the timeline. Hair loss that started two to three months after a major illness, surgery, or new medication is likely triggered by that event. Thinning paired with fatigue, weight changes, or feeling unusually cold or hot could signal a thyroid issue. If you’ve been on a restrictive diet or noticed other signs of nutritional deficiency like fatigue or brittle nails, low iron or protein intake may be a factor. Multiple causes can also overlap. A man with early genetic thinning who goes through a stressful period may notice an acceleration that’s driven by both pattern baldness and telogen effluvium simultaneously.