Why is my hair falling out? The common causes, and how to narrow them down

Nobody searches for this calmly. There is more hair in the drain than there used to be, or a photo shows more scalp than you remember, and every answer online seems to be either a supplement or a catastrophe.

The more useful question is what kind of loss this is, and you can get surprisingly far on that at home. What you cannot do at home is confirm a medical cause. This guide will help you describe what is happening clearly, and tell you when that description belongs in front of a doctor.

First, check it really is falling out

Two things regularly get mistaken for hair loss.

Normal shedding. Losing 50 to 100 hairs a day is ordinary. Each follicle runs on its own cycle of growth and rest, so some hairs are always finishing. Long hair makes the same number look like much more, and hair released between washes tends to come out all at once in the shower.

Breakage. Pick up some of the hairs you are finding and look at the ends. A full-length hair with a small pale bulb at one end was shed by the follicle. A shorter piece with no bulb and a blunt or frayed end snapped along its length, and that is a handling or damage problem rather than a follicle problem. The shedding or breakage guide walks through it, and it takes about thirty seconds.

If it is mostly breakage, the rest of this page is not your problem. If it is mostly bulbs and the amount has clearly risen, read on.

Read the pattern

Where and how the hair is going tells you more than how much is going. This table is a guide to what to raise with a doctor, not a way of diagnosing yourself, and more than one cause can apply at once.

Sudden hair loss: look backwards, not at your shampoo

Sudden, all-over shedding is usually telogen effluvium. Something pushes a large group of follicles into their resting phase at the same time, and because that phase lasts around three months, the hairs come out long after the event. By then you may feel perfectly well, which is why almost everyone blames the wrong thing.

The American Academy of Dermatology's list of common triggers is a good place to start:

• Giving birth, which has its own timeline
• A high fever, or recovering from an illness
• Surgery
• Significant weight loss (the AAD uses 20 pounds, about 9 kg, or more)
• Heavy stress, such as a divorce, a job loss or caring for someone who is ill
• Stopping the contraceptive pill

If you find a likely trigger and it has passed, the shedding generally stops by itself, and hair usually regains its normal fullness within six to nine months. If the trigger continues, so can the shedding. The telogen effluvium guide has the month-by-month version.

A milder rise that comes around the same time every year and fades within a couple of months may simply be seasonal shedding.

Causes of hair falling out in women

All of the causes above apply to anyone, but several come up especially often in women.

Female pattern hair loss. The most common long-term cause. It usually shows as a widening part and a thinner ponytail rather than a dramatic shed, and it is inherited. It has its own guide.

Childbirth. Postpartum shedding is extremely common and usually temporary.

Hormonal change. Polycystic ovary syndrome is a common cause, and is often accompanied by acne, irregular periods or extra facial and body hair. Stopping some contraceptive pills can cause a temporary shed. Pattern hair loss also becomes more common after the menopause.

Low iron. Low iron is a recognised cause of hair loss, and heavy periods make it more likely. Studies have found lower ferritin (stored iron) on average in women with non-scarring hair loss, although how much low iron causes the loss is still debated. Only a blood test can tell you, and iron is not something to take on spec.

Styles and chemical treatments. Tight braids, weaves and ponytails can cause traction alopecia, which can become permanent if the pulling goes on. Repeated colouring, perming or relaxing damages the hair, and severe damage to follicles can leave permanent bald spots.

Thyroid hair loss

Both an underactive and an overactive thyroid can cause thinning across the whole scalp. It tends to show up months after the thyroid problem begins, because of the long hair cycle, which makes the connection easy to miss.

The AAD notes that treating the thyroid condition can reverse the loss. Regrowth is not instant, though: hair has to work through its cycle again, and the UK's British Thyroid Foundation notes that shedding can briefly get worse at the start of treatment for an underactive thyroid. That is a reason to stay in touch with your doctor, not to stop your medication.

Scalp itching and hair loss

Itch alone is common and usually harmless. Most itchy, flaky scalps come down to seborrhoeic dermatitis or a stripped skin barrier. Itch that arrives together with hair loss needs a closer look, because the possibilities include:

• Ringworm of the scalp (tinea capitis). A fungal infection causing scaly, sometimes inflamed patches, often with black dots where hairs have broken off. Hair usually regrows once it has been treated.
• Scalp psoriasis. Hair usually regrows after the scalp clears, though it can take time.
• Lichen planopilaris and frontal fibrosing alopecia. Inflammatory conditions that destroy follicles and replace them with scar tissue. They can cause itching, burning or tenderness, and frontal fibrosing alopecia mainly affects women after the menopause, as a slowly receding band along the front hairline. The hair lost to scarring does not come back, but early treatment aims to protect what is left.

Medication and other medical causes

Many medicines list hair loss as a possible side effect. If the timing fits, ask the prescriber. Do not stop anything by yourself, because stopping some drugs abruptly can be dangerous.

Chemotherapy and radiotherapy to the head are the best-known causes. Less common ones include other infections, compulsive hair pulling (trichotillomania), and too much vitamin A or selenium, usually from supplements.

What a doctor is likely to check

Expect questions about timing, medication, diet, periods and family history, followed by a look at your scalp. Blood tests often include iron stores and thyroid function, plus hormones if there are signs of excess androgens. A small scalp biopsy is sometimes used when the cause is unclear.

You can make that appointment far more useful by bringing:

• The date the shedding started, and anything notable from the four months before it
• A list of medicines and supplements, including start and stop dates. If you take biotin, say so: it can interfere with some blood tests
• Photos of your part, taken in the same light

What to do this week

1. Do the bulb check and sort what you find into shed and broken hairs.
2. Write down what happened two to four months before this started.
3. Photograph your part and crown, so that you have something to compare with.
4. Be gentle with what is still attached, and do not overhaul your routine in a panic. New products rarely explain sudden shedding, and changing everything at once makes it impossible to see what helped.