Anagen effluvium (chemotherapy-induced hair loss)

Key takeaways

• It is the fast, severe cousin of telogen effluvium. Growing hairs lose their metabolic activity and break or fall within days to weeks, instead of the 2 to 3 month lag of telogen effluvium. Causes include chemotherapy, radiation, toxins and inflammatory diseases such as alopecia areata. Regrowth typically starts after 1 to 3 months, but occasionally the loss is permanent (Kanwar 2013).
• Chemo hair loss is common. A 2025 meta-analysis opens with an estimate that about 65% of chemotherapy patients are affected (Kearney 2025).
• Scalp cooling works, with a ceiling. In the SCALP trial (182 women with early breast cancer; 142 analysed), 50.5% of cooled women kept more than half their hair after 4 cycles versus 0% of controls (Nangia 2017). A meta-analysis of 8 breast cancer studies reported a 43% lower risk of chemotherapy alopecia (RR 0.57) (Contreras Molina 2024). See scalp cooling.
• Cooling may cut the risk of lasting loss. In a Korean open-label trial, persistent alopecia 6 months after chemotherapy was 13.5% (12 of 89) with cooling versus 52.0% (26 of 50) without (Kang 2024).
• Side effects of cooling are mostly discomfort. Across 67 studies, chills (42%), cap heaviness (35%) and headache (30%) were most common; 18% stopped early, and the pooled scalp metastasis rate was 0.15% (Kearney 2025).
• Persistent chemo alopecia has a consensus definition. A 2025 expert panel (15 experts) defined it as non-scarring hair loss persisting beyond 6 months after chemotherapy, with taxanes, thiotepa and anthracyclines as key contributors. It recommended prevention with scalp cooling and early topical or low-dose oral minoxidil, and advised against bicalutamide and oral finasteride or dutasteride in breast cancer patients because of safety concerns (Freites-Martinez 2025).
• Treatment of persistent loss is modest. In a retrospective cohort of 192 women, 67% with persistent chemo alopecia and 76% with endocrine-therapy alopecia improved moderately or significantly on topical minoxidil or spironolactone, but there was no control group (Freites-Martinez 2019).
• Endocrine therapy has its own pattern. Aromatase inhibitors and tamoxifen can cause pattern-type thinning, usually mild (grade 1 in 92% of 112 women), and 80% of 46 assessed improved on minoxidil in an uncontrolled review (Freites-Martinez 2018). Check with the oncology team before using any hormone-active hair drug.

What it is

In the growth phase the bulb cells divide very rapidly, so cytotoxic drugs and radiation hit them first. Radiotherapy to the scalp causes transient loss at lower doses and permanent loss at higher doses. Some drugs and toxins cause it too. Eyebrows, lashes and body hair also fall, and scalp cooling does not protect them.

After chemotherapy ends, regrowth typically starts within a few months, and new hair can differ in texture or colour for a time. Persistent loss is defined at 6 months.

What the studies show

See the key takeaways. Cooling effectiveness varies by drug regimen and by person; the SCALP trial included taxane-based (64%) and anthracycline-based (36%) regimens. Cooling is usually not used for blood cancers because of theoretical scalp relapse concerns, so ask your oncologist.

Hair type notes

• Hair type does not change whether chemo hair loss happens, but very dense or tightly coiled hair may reduce cooling-cap contact. Ask the cooling provider about fit.
• Heavily processed or very long hair is more fragile when thin, so gentle handling helps.

Bottom line

Before chemotherapy, ask about scalp cooling availability, cost and suitability for your regimen. Use gentle shampoos, soft brushes and low heat during treatment. If hair has not returned by 6 months after finishing chemotherapy, ask a dermatologist about persistent alopecia; topical minoxidil is an option the expert panel supports, while hormone-active drugs need oncology sign-off. Wigs, scarves and scalp micropigmentation can help confidence. Discuss with a doctor.