What Causes Hair Loss? The Main Types Explained

Noticing hair loss is unsettling, but here is the most useful thing to understand before you do anything about it: hair loss is not one condition. It is a symptom with many possible causes, and what helps depends entirely on which one you have. Shedding caused by stress behaves differently from genetic thinning, which behaves differently again from patchy autoimmune loss. This guide explains the main types, how to tell them apart, and when it is worth getting checked, so you can respond to what is actually happening rather than guessing.

First, a quick look at how hair grows

Every hair on your scalp cycles through three phases. The anagen phase is active growth, and at any moment roughly 85 to 90 percent of your hairs are in it, growing for anywhere from two to six years or more. The catagen phase is a brief transition lasting a couple of weeks. The telogen phase is rest: the hair stops growing, sits in the follicle for around three months, then sheds to make way for a new one.

Because of this cycle, losing hair every day is completely normal. Shedding roughly 50 to 100 hairs a day is just the cycle turning over. Hair loss becomes a condition when something disrupts the cycle, shrinks the follicles, or damages them, and the different ways that can happen are what define the different types.

Androgenetic alopecia: the most common cause by far

Androgenetic alopecia, also called pattern hair loss, is the cause behind the overwhelming majority of hair loss in both men and women. Estimates suggest it affects around half of men by age 50, with prevalence continuing to rise with age, and it is common in women too, particularly after menopause.

It is genetically driven. In people who carry the predisposition, hair follicles in certain areas of the scalp are sensitive to androgens, a group of hormones present in everyone. Over time, that sensitivity causes the follicles to miniaturise: each cycle, the hair they produce grows back slightly finer, shorter, and lighter, until thick terminal hairs are gradually replaced by fine, wispy ones.

The pattern differs by sex. In men it typically starts with a receding hairline at the temples and thinning at the crown, which can progress and eventually merge. In women it usually appears as diffuse thinning across the top of the scalp, often first noticed as a widening part line, while the front hairline generally stays where it is. Complete baldness is rare in women even with significant thinning.

Two things are worth knowing about pattern loss. It is progressive, meaning it continues gradually if nothing is done, which is why acting earlier preserves more. And it is manageable: a range of approaches exists, from clinical treatments to prescription options a doctor can discuss with you. Which is appropriate depends on your stage, sex, and health, which is exactly what a proper assessment works out. How our PRP hair regrowth treatment works

Telogen effluvium: sudden shedding after a shock

If your hair seems to be falling out everywhere at once, coming away in handfuls in the shower or on your pillow, telogen effluvium is the likely explanation. It is the most common cause of sudden, diffuse shedding, and the most common cause of non-scarring diffuse hair loss in women.

Here is the mechanism. A significant physical or emotional shock pushes a large share of your hairs out of their growth phase and into the resting phase prematurely. Around two to three months later, all those resting hairs shed at once. Common triggers include serious illness or high fever, surgery, childbirth, rapid weight loss or crash dieting, iron deficiency, thyroid problems, some medications, and periods of intense psychological stress.

The delay is the giveaway. Because of the two-to-three-month lag, the shedding often starts when the trigger has already passed, which makes it feel random and alarming. It usually is not. The reassuring news is that telogen effluvium is typically temporary: once the trigger resolves, the cycle normalises and hair commonly recovers over several months. When shedding continues beyond about six months, or no trigger can be identified, it is worth investigating properly, both to check for an ongoing cause such as a deficiency or thyroid issue and because persistent shedding can sit on top of early pattern loss and unmask it.

Alopecia areata: patchy loss with an autoimmune cause

Alopecia areata looks distinctly different from the two types above. Instead of overall thinning or diffuse shedding, it appears as one or more well-defined, smooth, round bald patches, usually appearing quite suddenly. It happens because the immune system mistakenly targets hair follicles, disrupting growth in the affected spots. It can affect the scalp, beard, eyebrows, or elsewhere, and in less common forms can involve the whole scalp or body.

Its course is unpredictable. Patches can regrow on their own, sometimes within months, and can also recur. Because it is a medical autoimmune condition rather than a cosmetic concern, alopecia areata should be assessed by a doctor or dermatologist, who can confirm the diagnosis and discuss the medical options available. If you notice a sudden smooth bald patch, seeing a professional promptly is the right move rather than waiting to see what happens.

Traction alopecia: loss caused by pulling

Traction alopecia is mechanical. Hairstyles that pull tightly and repeatedly on the same hairs, such as tight ponytails, buns, braids, cornrows, or extensions, place chronic tension on the follicles. Over time, that tension damages them, and hair thins where the pulling is greatest, classically around the hairline and temples.

Caught early, it is one of the most fixable forms of hair loss: loosening or varying the style takes the tension off and the follicles can recover. The catch is that prolonged traction can permanently scar the follicles, at which point the loss becomes irreversible. Early warning signs include soreness, small bumps around the hairline, and broken short hairs where the style pulls. If a style hurts, the follicles are under too much load.

Scarring alopecias: when follicles are destroyed

A smaller group of conditions, collectively called cicatricial or scarring alopecias, destroy the follicle itself and replace it with scar tissue. These include conditions such as frontal fibrosing alopecia, which causes a slowly receding band along the front hairline, most often in women after menopause, and lichen planopilaris. Signs that distinguish scarring types include redness, scaling, itching or burning in the affected area, and skin that looks shiny or smooth where follicle openings have disappeared.

These conditions are less common but more urgent, because follicles lost to scarring do not come back. The goal of medical care is to halt the process before more are lost. Any hair loss accompanied by an inflamed, itchy, painful, or visibly changed scalp warrants prompt assessment by a doctor or dermatologist.

Other causes worth knowing

A few additional causes come up regularly:

Nutritional deficiencies. Iron deficiency is a well-recognised contributor, particularly in women, and low levels of nutrients such as vitamin D, zinc, and protein can also affect the hair cycle. These usually show up as diffuse shedding rather than patterned loss, and blood tests can identify them.

Thyroid and hormonal conditions. Both an underactive and overactive thyroid can cause diffuse hair loss, and hormonal conditions such as polycystic ovary syndrome are associated with pattern-type thinning in women.

Medications and medical treatments. Some medicines list hair shedding among their effects, and chemotherapy causes a distinct, rapid form of loss called anagen effluvium because it interrupts hairs in their growth phase. Medication-related shedding is a conversation for your prescribing doctor; never stop a medicine on your own.

Scalp conditions. Fungal infection of the scalp (tinea capitis), severe seborrhoeic dermatitis, and psoriasis can all contribute to hair loss or breakage in affected areas. Treating the scalp condition is the first step. 

Postpartum shedding. The heavy shedding many women experience a few months after giving birth is a form of telogen effluvium driven by the hormonal shift after delivery. It is common, normal, and typically resolves on its own.

How the types compare at a glance

The pattern of your hair loss is the biggest clue to its cause. Gradual thinning in a defined pattern, at the temples and crown in men or along the part line in women, points to androgenetic alopecia. Sudden, heavy, all-over shedding two or three months after a stressful event points to telogen effluvium. Smooth, round bald patches point to alopecia areata. Thinning where a hairstyle pulls points to traction alopecia. And loss accompanied by an inflamed, itchy, or scarred-looking scalp points to a condition that needs prompt medical attention.

Real cases are often mixed, which is part of why self-diagnosis is unreliable. A period of heavy shedding can reveal underlying pattern loss that was quietly progressing. A deficiency can amplify genetic thinning. Untangling what is actually going on is precisely what a professional assessment is for.

When to act

Two principles are worth keeping in mind. First, for progressive types like pattern hair loss, earlier action preserves more, because it is far easier to keep the hair you have than to recover what is gone. Second, some presentations should not wait: sudden patchy loss, shedding that continues beyond six months, or any hair loss with scalp redness, pain, scaling, or itching deserves prompt professional attention.

If you are unsure which type you are dealing with, that is a normal place to be, and it is exactly the question an assessment answers. A consultation with a scalp analysis can identify the pattern of your loss, pick up signs that need medical follow-up, and give you a clear picture to base decisions on, whether or not you go on to treat it. 

Frequently asked questions

How much hair loss is normal per day?

Shedding around 50 to 100 hairs a day is a normal part of the hair cycle. Noticeably more than usual for you, sustained over weeks, is a better warning sign than any absolute number.

Is my hair loss from stress or genetics?

Timing and pattern are the clues. Stress-related shedding is diffuse and usually starts two to three months after a significant event, then settles. Genetic loss is gradual and patterned, at the temples and crown in men or the part line in women. The two can also overlap, which is where an assessment helps.

Does hair grow back after telogen effluvium?

Usually, yes. Once the trigger has passed, the hair cycle normalises and density commonly recovers over several months. Shedding that persists beyond about six months is worth investigating.

Can women get pattern hair loss?

Yes. Female pattern hair loss is common, particularly after menopause, and typically shows as widening of the part line and diffuse thinning on top rather than a receding hairline.

Which types of hair loss are reversible?

Telogen effluvium typically resolves once its trigger is addressed, early traction alopecia can recover when the tension is removed, and deficiency-related shedding can improve when the deficiency is corrected. Pattern hair loss is progressive but manageable, and scarring alopecias cause permanent loss in affected areas, which is why early attention matters.

Do I need to see a doctor about my hair loss?

See a doctor or dermatologist promptly for sudden patchy loss, or any loss with scalp redness, scaling, pain, or itching. For gradual thinning or ongoing shedding, a professional scalp assessment is a sensible first step to identify what is going on.

About this article

This article draws on peer-reviewed and clinical reference literature, including StatPearls’ clinical review of androgenetic alopecia (NCBI Bookshelf), epidemiological research on pattern hair loss prevalence, and dermatological studies of telogen effluvium and its causes (Journal of Cosmetic Dermatology, 2025). It is general information, not medical advice, and is not a substitute for an individual assessment by a qualified health professional.