Hair Loss Causes: Types and When to See a Doctor

Most people notice hair loss in one of three ways: more hair in the brush or shower drain, a part or hairline that looks different in photos, or a bald patch that was not there last month. Each of those points to a different group of causes, and some of them need a doctor much sooner than others.

This guide sorts the causes by what you can actually see, explains how to tell everyday shedding from true hair loss, and lists the signs that mean you should book an appointment instead of waiting.

The short answer

Losing roughly 50 to 100 hairs a day is normal shedding, not hair loss.
The most common cause worldwide is hereditary hair loss (male or female pattern hair loss), which develops gradually.
Sudden shedding all over the scalp often follows a trigger a few months earlier, such as an illness with fever, surgery, childbirth or a stressful period, and it usually settles on its own.
See a doctor promptly for bald patches, hair coming out in clumps, sudden loss, or a scalp that itches, burns, hurts or looks scarred.

Shedding or hair loss? Start here

Every hair on your scalp runs through its own cycle: a long growing phase, a short transition, then a resting phase that ends with the hair falling out so a new one can start. Because your follicles are out of step with each other, you lose some hair every day without your hair looking any thinner. The American Academy of Dermatology (AAD) puts normal shedding at 50 to 100 hairs a day.

Dermatologists separate two different situations:

Excessive shedding (the medical name is telogen effluvium). Many hairs move into the resting phase at the same time and fall out together a few months later. The follicles themselves are fine, so the hair usually comes back.
Hair loss. Something stops the hair from growing: inherited thinning, an immune reaction, certain medicines and treatments, or hairstyles that pull. The hair will not return until the cause is dealt with, and some types need treatment.

It is possible to have both at once, which is one reason a proper diagnosis matters before you spend money on products.

Quick check at home: look at a few hairs from your brush. A hair shed from the resting phase usually has a small, pale bulb at the root end (a “club hair”). Short pieces with no bulb at all point to breakage from heat, colouring or rough brushing, which is a hair-care problem rather than a follicle problem.

Read the pattern: what your hair loss looks like

The shape and speed of hair loss are the most useful clues you have before seeing anyone. Doctors start in the same place: how long it has been happening, and whether it came on gradually or all at once. Use the table to find the pattern closest to yours.

What you notice	Common causes	Can it grow back?	How soon to get checked
Receding hairline or thinning crown (men); widening part or thinning on top (women)	Hereditary hair loss, ageing	Treatment can slow it and may regrow some hair; it works best started early	Routine appointment
Sudden, heavy shedding all over the scalp	Telogen effluvium after illness, surgery, childbirth, big weight loss or stress; thyroid problems; low iron, protein or zinc; some medicines	Usually yes, once the trigger passes or is treated	Routine, or sooner if there is no obvious trigger
Round or oval bald patches with smooth skin	Alopecia areata	Often, although it can come and go	Soon
Patches with scaling, redness or tiny black dots	Scalp infection such as ringworm, scalp psoriasis	Usually, after treatment	Soon
Thinning along the hairline where hair is pulled back	Traction alopecia (tight braids, ponytails, buns, extensions)	Ongoing pulling can make it permanent; stopping early gives the best chance	Change styles now; book if it is not improving
Itching, burning or tenderness, with shiny scalp where hair has gone	Scarring alopecia (for example frontal fibrosing alopecia or CCCA)	Destroyed follicles cannot regrow; early treatment protects the hair you still have	As soon as possible, ideally with a dermatologist

Gradual thinning: usually hereditary

Hereditary hair loss (androgenetic alopecia) affects both men and women and is the most common cause of hair loss worldwide. Inherited genes make the follicles shrink over time until they stop producing visible hair. In men, the first sign is usually a receding hairline or a thin spot on top of the head. In women, it is more often a widening part or overall thinning, with the front hairline kept.

It can begin as early as the teenage years but usually starts later. Without treatment it tends to continue, so if it bothers you, earlier is better than later.

Sudden shedding: look for a trigger

The AAD lists common triggers for excessive shedding: losing 20 pounds (about 9 kg) or more, giving birth, a high fever, an operation, recovering from an illness, a period of heavy stress, and stopping birth-control pills. The shedding is spread across the whole scalp rather than in one spot. If the stress continues, so can the shedding.

Patches: immune system, infection or habit

Round, smooth patches are the classic sign of alopecia areata, a condition in which the immune system attacks hair follicles. It can also affect the beard, eyebrows or eyelashes. It is not contagious.

Patches with flaky, inflamed skin or small black dots (hairs broken off at the surface) suggest a scalp infection such as ringworm, which is contagious and common in children. Uneven patches of broken hair can also come from hair pulling (trichotillomania), which many people do without noticing, often when stressed. All three are treatable, and hair usually regrows if the follicles have not been damaged.

Scalp symptoms: the pattern not to ignore

In scarring alopecias, inflammation destroys the follicle and replaces it with scar tissue. Once that happens, no treatment can bring that hair back. The warning signs are itching, burning, tenderness or a smooth, shiny scalp where hair used to be. This is the group where waiting does the most harm.

Pattern checker

What could be behind your hair loss?

This checker gives general, indicative information based on public guidance from dermatology and health organisations. It is not a diagnosis and does not replace an examination by a doctor. If you are worried, book an appointment.

Causes that are easy to overlook

If your pattern does not match anything obvious, these are worth raising with a doctor:

Medicines. A new medicine or a change in dose can trigger shedding, typically a couple of months later. Do not stop a prescribed medicine on your own; ask the prescriber whether hair loss is a known side effect.
Thyroid problems. An overactive or underactive thyroid can thin the hair. Treating the thyroid condition can reverse it.
Low iron, protein, zinc or biotin. More likely after restrictive diets or rapid weight loss. Hair can regrow once levels are back to normal.
Hormonal changes. Polycystic ovary syndrome (PCOS) and coming off some birth-control pills can cause thinning in women.
Hair care. Frequent colouring, perming, relaxing and high heat weaken hair over time and can eventually damage follicles.
Too much of some supplements. Large amounts of vitamin A or selenium can themselves cause hair loss, so taking more is not automatically safer.

The timing trick: look back three months

Excessive shedding shows up well after the event that caused it, because the hairs that fall out had already stopped growing weeks earlier. That delay is why so many people cannot connect their shedding to anything.

Each hair’s cycle

Growth (anagen) years
Transition (catagen) weeks
Rest, then shed (telogen) months

Example: shedding after childbirth

BirthThe trigger
About 2 monthsExtra shedding often noticed
About 4 monthsShedding usually peaks
6 to 9 monthsFullness usually returns

Fever, surgery, stress and big weight loss follow a similar delay of a few months. Ongoing stress can keep shedding going.

Excessive shedding usually appears a few months after its trigger. Timings as described by the American Academy of Dermatology; individual timing varies.

The AAD gives childbirth as a clear example: new mothers often notice extra shedding about two months after giving birth, it usually peaks around four months, and hair tends to regain its normal fullness within six to nine months.

Here is how to use that in practice. Say you had flu with a high fever in January. Heavier shedding in March or April fits the usual pattern, and you would expect it to ease over the following months. Shedding that starts in March with nothing unusual in the months before is the situation to get checked, because the cause may be something ongoing, such as a thyroid problem or low iron.

When to see a doctor

See a doctor soon (within days or a couple of weeks) if you have:

bald patches, especially round ones, or patches in your beard, eyebrows or eyelashes;
hair coming out in clumps, or sudden loss with no obvious reason;
a scalp that itches, burns, hurts, is red or scaly, or looks shiny where hair has gone;
hair loss that started after a new medicine (keep taking it and contact the prescriber);
hair loss in a child.

Book a routine appointment if:

gradual thinning is bothering you and you would like to know your options;
shedding has lasted longer than about six months;
you also feel unusually tired, cold, have noticed weight changes or irregular periods.

Reasonable to watch and wait if:

the shedding began a few months after a clear trigger, is spread evenly with no patches, and is starting to ease. Take a photo now in good light so you can compare later.

Whatever the cause, it is also worth talking to a doctor if hair loss is affecting your mood or confidence. That is a valid reason on its own.

Who to see first

In the US, you can often book a board-certified dermatologist directly, although some insurance plans need a referral. In the UK, Canada and Australia, the usual first step is your GP or family doctor, who can examine your scalp, order blood tests and refer you to a dermatologist if needed. The NHS advises seeing a GP before paying a commercial hair clinic, which can be costly.

What happens at the appointment

A dermatologist will ask questions, look closely at your hair and scalp (often with a magnifying device called a dermatoscope), and may suggest blood tests or a small scalp biopsy if they suspect a disease, a deficiency, a hormone imbalance or an infection. Many cases can be identified from the history and examination alone.

You will get more out of the visit if you bring:

when you first noticed the change, and whether it was sudden or gradual;
anything significant from the past six months: illness, surgery, childbirth, diets, stress;
every medicine and supplement you take, including recent dose changes;
family history of hair loss on either side;
your usual styles and treatments (braids, extensions, colouring, relaxers, heat);
a few photos of the same area taken over time in similar light.

How treatment depends on the cause

There is no single hair loss treatment, which is exactly why the diagnosis comes first. Broadly:

Shedding after a trigger usually needs no treatment beyond time and gentle hair care.
Thyroid problems, deficiencies and infections are treated at the source, and hair often recovers once they are under control.
Hereditary hair loss can be slowed with medicines such as minoxidil, available without a prescription. The AAD notes that results usually take 6 to 12 months and the medicine has to be continued to keep them. A doctor may discuss prescription options as well.
Alopecia areata may be treated with steroid injections or creams applied to the patches, among other options.
Hair transplant surgery is an option for some people with stable hereditary hair loss and enough donor hair, but it is not a first step and does not stop future thinning.
Cosmetic options such as a shorter cut, hair fibres, wigs or scalp micropigmentation can help at any stage.

Be cautious with anything sold as a cure for every kind of hair loss. Supplements, for example, help only if you are actually low in a nutrient.

Frequently asked questions

Is hair loss contagious?

No. You cannot catch hair loss from someone else. The exception is a fungal scalp infection such as ringworm, which spreads through contact and shared combs or hats and can lead to hair loss if it is not treated.

Will my hair grow back?

It depends on the cause. Shedding after a trigger usually recovers within six to nine months. Alopecia areata often regrows. Hereditary hair loss tends to continue without treatment, and hair lost to scarring alopecia does not return, which is why early diagnosis matters.

Should I see a dermatologist or a hair clinic first?

A doctor first. A GP or dermatologist can diagnose the cause, order tests and treat medical conditions. Commercial clinics often focus on selling their own treatments, and a treatment that does not match the cause wastes time and money.

Can stress cause permanent hair loss?

Stress-related shedding is usually temporary and stops once the stressful period passes, although ongoing stress can keep it going. If shedding does not improve, get checked, because another cause may be present alongside it.

Your next step

Take a few photos today (hairline, part and crown) in the same light, write down anything significant from the last six months, and check your situation against the “see a doctor soon” list above. If nothing there applies and you can name a trigger, give it time and compare your photos in a couple of months. If something does apply, book the appointment now.

This article is for informational purposes only and is not professional medical advice. Talk to a qualified healthcare professional about your own symptoms before starting, stopping or changing any treatment.

Written by the Hair Loss Compass Editorial Team · Last reviewed: October 23, 2026

Hair Loss Explained: Causes, Types and When to See a Doctor