Dandruff

Key takeaways

• Dandruff is common and chronic. Industry researchers estimate it affects as many as half of people at some point after puberty (Turner 2013). Scalp seborrheic dermatitis, the inflamed form on the same spectrum, affects about 4.4% of people worldwide (5.6% of adults) in a meta-analysis of 121 studies (Polaskey 2024).
• Three things interact: skin oil, yeast and your skin's sensitivity. Sebum feeds Malassezia yeast, whose enzymes release irritating free fatty acids in people prone to flaking (Ro and Dawson 2005). Dandruff scalps also have a weaker barrier with fewer protective lipids (Harding 2002; Turner 2012). See scalp health and oxidized sebum.
• Dandruff is not dry skin and not dirt. Moisturising oils do not fix it, it can occur on oily scalps, and washing more often does not cause it.
• Antifungal shampoos work. Ketoconazole 2%, zinc pyrithione 1%, selenium sulfide, piroctone olamine and ciclopirox all beat controls in trials. Ketoconazole beat zinc pyrithione in a 331-person trial in severe cases (Pierard-Franchimont 2002).
• It relapses when you stop. In a randomized double-blind study, people who switched from an anti-dandruff to a plain shampoo showed worsening scalp markers after about 3 days and visible flaking after about 3 weeks (Locker 2025, industry). In another trial, weekly ketoconazole cut 6-month relapse from 47% to 19% (Peter 1995).
• In pooled data from 17 trials, men responded more to zinc pyrithione than women (Collins 2018). A selenium sulfide shampoo worked across all hair types in 93 people (Reygagne 2025).
• Red flags that this is not simple dandruff: hair loss, oozing, crusting, painful bumps, thick silvery plaques, or no improvement after 4 weeks of an antifungal shampoo. See scalp psoriasis, seborrheic dermatitis, scalp folliculitis, and, in children, tinea capitis.

The science

Dandruff is the mild end of the seborrheic dermatitis spectrum, confined to the scalp, with flaking and often itch but little visible redness. The scalp's bacterial and fungal network "collapses" in dandruff and seborrheic dermatitis, as found in 102 Koreans (Park 2017). Dandruff scalps carry more Malassezia restricta and Staphylococcus capitis and less Cutibacterium acnes, a pattern that reverses with effective treatment (Hu 2024). Severity relates to microbiome differences and differs by sex (Liang 2025).

Both lipid-barrier studies (Harding 2002, Turner 2012) came from Unilever and found lower intercellular lipids and impaired barrier function on dandruff scalps. On diet, a systematic review of 13 studies found associations of seborrheic dermatitis with a Western diet and alcohol and with lower zinc and vitamin D, and an 8-week prebiotic trial lowered scalp sebum. These are weak, mostly case-control data (Woolhiser 2024).

What it means by hair profile

• Straight, fine or oily hair: daily or alternate-day antifungal use is easy; watch residue and silicone buildup.
• Wavy to coily hair (2A-4C): sebum does not travel down the shaft, so the scalp can be flaky while the lengths are dry. Weekly washing was recommended for afro-textured hair to ease dandruff in one study (Fajuyigbe 2024). Apply medicated shampoo to the scalp only, then condition the lengths.
• Scalp type: oily, balanced and flaky-or-itchy scalps can all have dandruff.

Myths and facts

• Myth: dandruff means a dry scalp. Fact: the mechanisms involve yeast, sebum and barrier function, not simple dryness.
• Myth: wash less and it will go away. Fact: frequent washing with an effective shampoo controls it, and stopping treatment brings flaking back (Locker 2025).
• Myth: dandruff causes hair loss. Fact: no evidence it causes permanent loss, though severe scratching or a second condition can add to shedding.
• Myth: apple cider vinegar or oils cure it. Fact: there is no trial evidence, and oils can feed Malassezia.

Bottom line

Start with an over-the-counter antifungal shampoo (ketoconazole, zinc pyrithione, selenium sulfide or piroctone olamine). Wash two to three times a week and leave it on for the label time. Judge after about 4 weeks; if the flaking clears, drop to weekly maintenance rather than stopping. If one active fails, rotate to another, since they work differently. Use a gentle shampoo on other days and condition the lengths. See a clinician for hair loss, redness, crusts, no response, or children with patchy flaking. Discuss with a doctor.