Anagen effluvium: sudden hair loss from treatments

Most hair shedding people worry about is telogen effluvium, where many hairs move into the resting phase at once and fall out a few months after a trigger. Anagen effluvium is different. It happens while hairs are still in their active growing phase, so the loss is faster and often much heavier ¹.

What happens in the follicle

Hair is made by rapidly dividing cells at the base of the follicle. When something disrupts that cell division, the hair becomes narrowed at its base and breaks easily ¹. The result is sudden shedding of damaged hairs, often over just days to weeks. Anagen effluvium does not scar the scalp ¹.

Common causes

According to DermNet, causes include ¹:

• Chemotherapy, especially when several drugs are used together or at high doses. Some drugs are more likely to cause severe hair loss than others.
• Radiation to the scalp.
• Severe scalp infection, such as a fungal infection that leaves swollen, tender bald patches.
• Autoimmune conditions, including alopecia areata and its more extensive forms. See alopecia areata.

Hair loss is a well-known side effect of chemotherapy, and the NHS describes it as temporary ². Not every chemotherapy drug causes hair loss, so ask your care team what to expect from your specific treatment.

What it looks like

Anagen effluvium usually causes abrupt shedding of much or all of the scalp hair, and often body hair too, including eyebrows and eyelashes ¹. Up to 90% of hair may be lost over a period of weeks ¹. With chemotherapy, hair loss typically starts within 2 to 4 weeks of treatment ¹.

Doctors usually diagnose it from a careful history, especially of recent medicines, and by examining the scalp and the shed hairs ¹.

Can scalp cooling help?

Scalp cooling is listed by DermNet as a suggested approach during chemotherapy ¹. It works by chilling the scalp during treatment, which is thought to reduce the amount of drug reaching the follicles.

The best-known trial is the SCALP study, published in 2017. It enrolled 182 women with early breast cancer at 7 US sites ³. Among women assessed:

• 50.5% of those who used scalp cooling kept their hair (48 of 95), meaning they had lost less than half ³.
• None of the women without scalp cooling kept their hair (0 of 47) ³.
• Side effects of cooling were mild to moderate only ³.

The researchers said longer-term research is still needed ³. So scalp cooling helped about half of these women, but not everyone, and results may differ with other cancers and drug combinations. Whether it is suitable for you is a decision for your cancer team.

Will hair grow back?

For most people, yes. DermNet describes anagen effluvium as reversible: the follicle resumes normal activity after the cause is removed ¹.

• After chemotherapy, hair usually recovers within 3 to 6 months of stopping ¹.
• Hair sometimes starts to grow back even while chemotherapy continues ¹.
• New hair may come back different. People with straight hair sometimes find it grows back curly, and the colour may change ¹.
• After radiation to the scalp, new growth may be incomplete or may not happen ¹.
• When the cause is alopecia areata, recovery is unpredictable ¹.

Coping while hair is lost

Practical steps many people find helpful:

• Plan ahead. Some people cut their hair short before treatment so the change feels less sudden.
• Choose a wig or head covering early. Matching a wig to your natural colour and style is easier before hair falls out. See choosing a wig.
• Protect the scalp. A bare scalp needs sun protection and warmth.
• Be gentle with new growth. Use a mild shampoo, a soft brush and avoid harsh chemical treatments until hair is stronger.
• Eyebrows and lashes. Makeup can help while they grow back. See eyebrow hair loss and camouflage options.
• Get support. Hair loss during illness can be distressing. Your care team can point you to local support services ².

When to seek advice

• Sudden heavy hair loss without an obvious cause such as chemotherapy needs a medical review.
• Patchy loss with a swollen, tender or pus-filled scalp may be an infection and needs prompt treatment.
• If hair has not started growing back several months after treatment ends, ask your doctor.

Let your care team know about any side effects during cancer treatment, as they may be able to help ². For other types of shedding, see chronic telogen effluvium and first steps after noticing hair loss.

Frequently asked questions

What is the difference between anagen and telogen effluvium?

Anagen effluvium happens during the growing phase and causes sudden heavy loss; telogen effluvium is shedding of resting hairs, usually months after a trigger ¹.

How soon does chemotherapy hair loss start?

Usually within 2 to 4 weeks of starting chemotherapy ¹.

Does scalp cooling work?

In one trial of women with early breast cancer, 50.5% who used cooling kept their hair, compared with none without it ³.

Will my hair grow back after chemotherapy?

In most cases hair recovers within 3 to 6 months of stopping, though texture and colour may change ¹.

Educational content. Not medical advice.