Hair loss in men has several distinct causes, and the most common one by far is genetic. Roughly 30% of men show signs of pattern baldness by age 30, 50% by age 50, and the percentage keeps climbing each decade after that. But genetics isn’t the only explanation. Autoimmune conditions, stress, medications, nutritional gaps, and even certain hairstyles can all trigger hair loss in men, each through a different biological mechanism.
Male Pattern Baldness: The Most Common Cause
Androgenetic alopecia, or male pattern baldness, accounts for the vast majority of hair loss in men. It’s driven by a hormone called dihydrotestosterone (DHT), which is converted from testosterone in the body. DHT binds to receptors on hair follicles and essentially tells them to shrink. Over time, affected follicles produce thinner, shorter, lighter hairs until they stop producing visible hair altogether. This process is called follicle miniaturization.
The pattern is predictable. It typically starts with a receding hairline at the temples, forming an M or V shape, and thinning at the crown. In later stages, these two areas merge until only a horseshoe-shaped band of hair remains around the sides and back of the head. Clinicians use a seven-stage scale to track progression: stage 1 shows no real change, stage 3 is where clinically significant balding becomes visible, and stage 7 leaves only a thin band of fine hair around the sides.
What determines whether you’ll develop pattern baldness is largely written into your DNA. A study published in The American Journal of Human Genetics found that variation in the androgen receptor gene, located on the X chromosome, is the single biggest genetic factor in early-onset male pattern baldness, with an estimated contribution of 46% to overall risk. Because this gene sits on the X chromosome, which men inherit from their mothers, the maternal side of your family tree is especially relevant to your risk. That said, the condition is polygenic, meaning multiple genes across both parents contribute.
Alopecia Areata: When the Immune System Attacks
Alopecia areata is a completely different condition from pattern baldness. It’s autoimmune, meaning the body’s own immune system mistakenly targets hair follicles. The attack is led primarily by a specific type of white blood cell (CD8+ T cells) that infiltrates the tissue around follicles in such dense clusters that pathologists describe it as a “swarm of bees” under the microscope. Natural killer cells, mast cells, and other immune cells join in.
The hair loss looks different, too. Instead of a gradual recession, alopecia areata typically causes round, smooth patches of baldness that appear suddenly. Some men experience just one or two small patches. Others lose all scalp hair (alopecia totalis) or all body hair, including eyebrows and eyelashes (alopecia universalis). The condition can come and go unpredictably, with hair regrowing in one area while falling out in another.
What triggers the immune system to turn on follicles isn’t fully understood, but it involves a breakdown in the hair follicle’s natural immune protection. Healthy follicles have a kind of biological shield that hides them from the immune system. When that shield fails, the immune system recognizes proteins in the follicle as foreign and launches an attack.
Telogen Effluvium: Stress-Related Shedding
Telogen effluvium is temporary, diffuse hair thinning triggered by a physical or emotional shock to the body. Rather than affecting specific areas, hair falls out more or less evenly across the scalp. The cause is a disruption to the hair growth cycle: a stressor pushes a large number of follicles into their resting phase simultaneously, and two to three months later, those hairs fall out all at once.
Common triggers include high fever, severe infections, major surgery, rapid weight loss, extreme psychological stress, and thyroid disorders (both overactive and underactive). Certain diets that are very low in protein can also set it off. The good news is that telogen effluvium resolves on its own once the underlying trigger is addressed, typically within three to six months, though full recovery can take up to eight months.
Medications That Cause Hair Loss
A surprisingly wide range of medications can trigger hair thinning or shedding as a side effect. The mechanism usually resembles telogen effluvium, where the drug pushes follicles into their resting phase prematurely.
- Blood thinners: Heparin, warfarin, and newer anticoagulants like rivaroxaban and apixaban are all linked to hair loss.
- Blood pressure drugs: Beta blockers such as propranolol, atenolol, and metoprolol, along with ACE inhibitors as a class, can contribute.
- Psychiatric medications: Valproate, used for epilepsy and mood disorders, causes hair loss in roughly 11% of patients. Certain antidepressants and antipsychotics carry the risk as well.
- Retinoids: Isotretinoin and other vitamin A derivatives used for acne are well-known culprits.
- Weight loss drugs: Semaglutide (Wegovy) and similar medications can contribute to hair shedding through multiple pathways, including the rapid weight loss they produce.
- Chemotherapy drugs: These cause the most dramatic hair loss because they directly target rapidly dividing cells, which includes hair follicle cells.
In most cases, hair regrows after the medication is stopped or adjusted, though the timeline varies.
Nutritional Deficiencies
Hair follicles are among the most metabolically active cells in the body, and they need a steady supply of certain nutrients to function. The deficiencies most commonly linked to hair loss are iron (measured as ferritin in blood tests), zinc, vitamin D, and B vitamins. Excess vitamin A and selenium can also cause shedding, which is one reason high-dose supplements aren’t always better.
Zinc plays a particularly important role because it’s involved in protein synthesis and cell division, both of which are essential during the active growth phase of hair. Low zinc levels show an especially strong correlation with alopecia areata. Iron deficiency, even without full-blown anemia, can contribute to diffuse thinning. These causes are treatable and often reversible once levels are corrected through diet or supplementation.
Scalp Conditions and Inflammation
Chronic inflammation on the scalp can damage follicles enough to interfere with hair growth. Seborrheic dermatitis is one of the more common examples. It occurs when the scalp overproduces oil (sebum), creating an environment where a naturally occurring yeast called Malassezia overgrows. The result is redness, flaking, and itching. The inflammation itself can hinder follicle function, and repeated scratching compounds the damage by physically disrupting follicles and obstructing new growth.
Traction Alopecia: Damage From Hairstyles
Traction alopecia results from prolonged tension on the hair. In men, this can come from tightly pulled ponytails, buns, cornrows, locs, or braids. Military personnel and others required to pull their hair back tightly for work are at higher risk. Even the constant rubbing of a hat or head covering can contribute over time, especially if hair is pulled back underneath.
Early signs include pain or stinging on the scalp, small bumps, and crusting. At this stage, the damage is reversible if you change the hairstyle. But if the pulling continues long enough, the follicles scar over and the hair loss becomes permanent. Where hair once grew, you’ll see smooth, shiny skin that won’t produce new growth. The key distinction with traction alopecia is that it’s entirely preventable and, when caught early, entirely reversible.