Alopecia (Hair Loss)

How hair grows and why it falls out

Each follicle cycles through a growth phase (anagen), lasting 2 to 7 years on the scalp, a short transition phase, and a resting phase (telogen) of about 3 months, after which the hair is shed. Losing 50 to 100 scalp hairs a day is normal. Alopecia happens when:

• more follicles than usual enter the resting phase at once (telogen effluvium)
• follicles shrink and produce finer, shorter hairs (pattern hair loss)
• the immune system attacks follicles (alopecia areata)
• follicles are destroyed and replaced by scar tissue (scarring alopecia)
• hair shafts break from damage or pulling

Types of alopecia

Androgenetic alopecia

The most common type, affecting at least half of men by age 50 and many women, especially after menopause. In men it causes a receding hairline and crown thinning. In women it causes diffuse thinning over the top of the scalp with a widening part, while the front hairline usually stays.

Alopecia areata

The immune system attacks hair follicles, causing well-defined smooth bald patches that can appear within days. Short "exclamation mark" hairs may be seen at the edges. Nails may be pitted. It can progress to total scalp hair loss (alopecia totalis) or loss of all body hair (alopecia universalis). It affects all ages, often starts in childhood or young adulthood, and is linked with thyroid disease, vitiligo and atopic conditions.

Telogen effluvium

Shedding increases 2 to 4 months after a trigger such as childbirth, a high fever, COVID-19, surgery, crash dieting, severe stress or a new medicine. Hair comes out in handfuls when brushing or washing, but you do not go bald. Regrowth usually follows within 6 to 12 months once the trigger has passed.

Medical causes to check

• Thyroid disorders, both underactive and overactive. See thyroid disorders.
• Iron deficiency, even without anemia, especially in women with heavy periods.
• Lupus and other autoimmune conditions.
• PCOS and other causes of high androgens in women.
• Medicines: chemotherapy, some anticoagulants, retinoids, some antidepressants, high-dose vitamin A, and stopping birth control pills.
• Severe protein, zinc or biotin deficiency (biotin deficiency is rare).
• Secondary syphilis, which causes "moth-eaten" patchy loss.

Diagnosis

A dermatologist will ask about the pattern and speed of loss, recent illnesses, pregnancy, diet, medicines, hair care practices and family history. Examination includes:

• the pull test: gently pulling about 50 to 60 hairs; more than about 10 percent coming out suggests active shedding
• dermoscopy (trichoscopy): a magnified view of the scalp and follicles
• looking for scarring, redness, scale and broken hairs
• checking nails, brows, lashes and body hair

Blood tests may include ferritin (iron stores), thyroid function, blood count, vitamin D, and androgen levels in women with signs of excess. Scrapings or hair samples identify fungal infection. A scalp biopsy confirms scarring alopecia or uncertain cases.

Treatment

Pattern hair loss

• Minoxidil foam or solution applied to the scalp, available over the counter for men and women. It takes 4 to 6 months to show results and must be continued; stopping leads to loss of regained hair. Low-dose oral minoxidil is increasingly prescribed.
• Finasteride tablets for men, which block conversion of testosterone to DHT. Not for women who could become pregnant.
• Spironolactone for some women with pattern loss.
• Low-level laser devices and platelet-rich plasma injections: modest evidence.
• Hair transplant surgery for stable, established loss.

Alopecia areata

• Steroid injections into patches for limited disease.
• Strong topical steroids, particularly in children.
• Topical immunotherapy for extensive disease.
• JAK inhibitor tablets (such as baricitinib and ritlecitinib) for severe alopecia areata, which can regrow hair in a substantial proportion of patients.
• Many small patches regrow on their own within a year.

Other types

• Telogen effluvium: treat the trigger, correct deficiencies, and wait for regrowth.
• Tinea capitis: oral antifungal medicine (creams alone do not work).
• Traction alopecia: loosen hairstyles and avoid tight extensions.
• Trichotillomania: habit-reversal therapy.
• Scarring alopecia: early anti-inflammatory treatment to stop further loss.

Cosmetic options

Hair fibers, wigs, hairpieces, scalp micropigmentation and changes in styling can make a big difference to confidence while treatment takes effect.

Living with alopecia

Hair loss can affect self-esteem, mood and social life. Support groups, counseling and dermatologists experienced in hair disorders help. Protect a bare scalp from the sun with a hat or sunscreen.

Frequently asked questions

What are the main types of alopecia?

The main types are androgenetic alopecia (pattern hair loss), telogen effluvium (temporary shedding), alopecia areata (autoimmune patchy loss), traction alopecia (from tight hairstyles), and scarring alopecias. Fungal infection and hair pulling are other causes. Each has a different treatment.

Does alopecia areata grow back?

Often, yes. Many people with a few small patches regrow hair within a year, sometimes without treatment. It can come back later. Extensive or long-lasting alopecia areata is less likely to regrow on its own, but steroid injections and JAK inhibitors can help.

What causes sudden hair loss?

Sudden diffuse shedding is usually telogen effluvium, 2 to 4 months after childbirth, illness, high fever, surgery, crash dieting or stress. Sudden round bald patches suggest alopecia areata. Thyroid problems, iron deficiency and new medicines are other causes worth checking.

Can stress cause alopecia?

Yes. Severe physical or emotional stress can trigger telogen effluvium, causing heavy shedding a few months later, and can trigger flares of alopecia areata in some people. Stress can also drive hair pulling. Stress-related shedding usually recovers once the stress passes.

Is alopecia permanent?

It depends on the type. Telogen effluvium, most alopecia areata and early traction alopecia are reversible. Pattern hair loss is progressive but can be slowed or partly reversed with treatment. Scarring alopecias permanently destroy follicles, so early diagnosis matters.