The medical term for hair loss is alopecia. It’s a broad term that covers everything from gradual thinning on top of your head to sudden patches falling out overnight to complete loss of body hair. Alopecia isn’t a single condition. It’s a category with several distinct types, each with different causes, patterns, and outcomes.
How Common Hair Loss Actually Is
Hair loss is far more widespread than most people assume. By age 35, about two-thirds of American men will notice some degree of thinning. By 50, roughly 85% of men have significantly thinner hair. Women are affected too: around 12% of women begin losing hair by age 30, and by 65 that number climbs to 37%.
For context, losing hair every day is completely normal. The average person sheds between 50 and 150 hairs daily as part of the natural growth cycle. Hair loss becomes a medical concern when shedding outpaces regrowth, or when follicles stop producing new hair altogether.
Androgenetic Alopecia: Pattern Baldness
The most common type of hair loss is androgenetic alopecia, better known as male-pattern or female-pattern baldness. This is the hereditary, age-related thinning that accounts for the vast majority of hair loss cases. A quarter of men start losing hair this way before they turn 30.
The mechanism involves a hormone called DHT, which is a byproduct of testosterone. Hair follicles have receptors that respond to DHT, and in people genetically prone to pattern baldness, those receptors are more sensitive than normal. When DHT overstimulates a follicle, it shortens the active growth phase. Each new hair comes in thinner and shorter than the last, and eventually the follicle stops producing visible hair at all.
In men, this typically starts with a receding hairline at the temples and thinning at the crown. Doctors measure progression using the Norwood scale, a seven-stage system that ranges from no significant loss (stage 1) to only a thin band of hair remaining around the sides and back of the head (stage 7). In women, the pattern is different. Hair usually thins diffusely across the top of the scalp while the hairline stays intact.
Alopecia Areata: Patchy, Autoimmune Hair Loss
Alopecia areata is an autoimmune condition in which the immune system mistakenly attacks hair follicles, causing inflammation that shuts down hair production. It typically shows up as sudden, coin-sized bald patches on the scalp, though it can affect the beard, eyebrows, eyelashes, or any body hair. The bare patches usually have no redness, rash, or scarring. Some people feel tingling or burning on the skin just before the hair falls out.
One telltale sign is “exclamation point” hairs around the edges of a patch. These are short, broken strands that are narrower at the base than the tip. Nail changes like tiny pits or dents also occur in some cases, especially when hair loss is more extensive.
Alopecia areata comes in three main forms. Patchy alopecia areata, the most common, involves one or more isolated spots of loss. Alopecia totalis means losing all or nearly all scalp hair. Alopecia universalis, which is rare, involves complete or near-complete loss of hair on the scalp, face, and body.
Both genetics and environmental factors appear to play a role. People with other autoimmune conditions like thyroid disease, psoriasis, or vitiligo are more likely to develop it, as are people with allergic conditions like eczema or hay fever. Emotional stress or illness can sometimes trigger an episode in someone who’s already predisposed, but most cases have no obvious trigger.
Telogen Effluvium: Stress-Related Shedding
Telogen effluvium is the type of hair loss people typically mean when they say stress made their hair fall out. Your hair grows in cycles: an active growth phase, a transitional phase, and a resting phase called telogen. Normally, only a small percentage of your hair is in the resting phase at any given time. With telogen effluvium, a physical or emotional stressor pushes up to 70% of actively growing hairs into the resting phase all at once. Two to three months later, those hairs shed in large quantities.
Common triggers include major surgery, childbirth, severe illness, significant weight loss, high fever, or intense emotional stress. The good news is that telogen effluvium is almost always temporary. The heavy shedding period lasts three to six months, and once the underlying cause is addressed, most people see full regrowth within six to eight months without any treatment.
Anagen Effluvium: Hair Loss During Active Growth
Anagen effluvium is sudden, widespread hair loss caused by damage to hair follicles while they’re actively growing. The cells at the base of each follicle are among the fastest-dividing cells in your body, which makes them vulnerable to anything that disrupts cell division. When those cells stop working, the hair strand becomes thin and weak, then breaks off near the scalp.
This type of hair loss is most commonly associated with chemotherapy. More than half of people undergoing chemotherapy experience it, typically noticing signs about two weeks after treatment begins. It can also follow certain medications and scalp surgeries. One distinctive feature is that people often keep hair along their hairline while the rest of the scalp thins dramatically. Hair typically regrows after the triggering treatment ends.
Traction Alopecia and Other Types
Traction alopecia results from repeated physical stress on the hair. Tight ponytails, braids, cornrows, extensions, and other hairstyles that pull on the hair over long periods can damage follicles and cause hair loss, particularly around the hairline and temples. Caught early, this type is reversible by changing hairstyles. If the pulling continues for years, the damage to follicles can become permanent.
Frontal fibrosing alopecia, which is becoming increasingly common in menopausal women, causes the hairline to gradually recede from the front of the scalp. Unlike pattern baldness, it involves scarring that can make the loss permanent. Trichotillomania is a hair-pulling disorder where a person repeatedly pulls out their own hair, often from the scalp, eyebrows, or eyelashes.
How Doctors Figure Out Which Type You Have
A dermatologist can usually narrow down the type of hair loss through a combination of simple tests. The process starts with questions about when the loss began, what pattern it follows, your hairstyle habits, family history, and any recent illnesses or stressors.
The physical exam focuses on inflammation, redness, scarring, and the pattern of thinning. A pull test involves grasping about 40 strands from different parts of the scalp and gently tugging. If six or more strands come out, that indicates active hair loss. A tug test checks whether individual strands break in the middle, which points to brittle or structurally weakened hair. Some dermatologists use a high-definition microscopic camera that magnifies the scalp up to 100 times, allowing them to count hairs and measure strand thickness precisely.
If the cause isn’t clear from the exam, blood tests can check for thyroid problems, iron deficiency, or other underlying conditions. A scalp biopsy or fungal culture may be needed to rule out infections like ringworm or to identify scarring conditions.
Treatment Options by Type
Treatment depends entirely on which type of alopecia you have. For androgenetic alopecia, two FDA-approved medications are available. Minoxidil is a topical solution you apply directly to the scalp, available over the counter for both men and women. Finasteride is a prescription pill approved for men that works by reducing DHT levels. Both require ongoing use to maintain results.
Telogen effluvium generally resolves on its own once the trigger is removed. Anagen effluvium from chemotherapy also tends to reverse after treatment ends, though the new hair may initially come in with a different texture or color. Alopecia areata is less predictable. Hair may regrow spontaneously, but it can also fall out again. Treatment focuses on calming the immune response in the affected areas.
Traction alopecia is the most preventable form. Switching to looser hairstyles and avoiding constant tension on the hair is both the treatment and the best protection against permanent damage.