What it is
Shampoo is a detergent for your scalp. Its job is to remove oil, sweat, flakes and product build-up. The main choices are how strong the cleansing is (sulfate shampoos lather and clean hard; milder or 'low-poo' formulas suit dry, curly or color-treated hair) and whether it carries a medicated active.
Anti-dandruff shampoos are where the evidence is. Dandruff and seborrheic dermatitis are driven partly by an overreaction to *Malassezia*, a yeast on everyone's scalp. Ketoconazole, ciclopirox, zinc pyrithione, selenium sulfide, salicylic acid and coal tar all target flaking. Everything else on the label, from biotin to caffeine to rosemary, spends a minute or two on your scalp before being rinsed away.
How strong is the evidencemoderate
A Cochrane review of 51 trials found ketoconazole and ciclopirox clear seborrheic dermatitis better than placebo over about four weeks, with low- to moderate-quality evidence and little long-term data. Other anti-dandruff actives have supportive but smaller trials. There is no good evidence that 'growth' shampoos regrow hair; a small ketoconazole study in pattern hair loss is a hint, not proof.
The claims you’ll meet5 checked
Anti-dandruff shampoo controls flakingHolds upKetoconazole and ciclopirox beat placebo in trials; zinc pyrithione and selenium sulfide are also established actives.
Shampoo can regrow hairUnprovenGrowth claims rest on ingredients without controlled evidence. Topical minoxidil is the non-prescription product with trials.
'Thickening' shampoo makes hair fullerMixedCoating polymers can make strands look fuller; it's cosmetic and washes out, not regrowth.
Sulfates damage hair or are toxicMixedStrong sulfates can dry out curly or color-treated hair and irritate a sensitive scalp, but they are not a cancer or hormone concern.
Washing too often causes hair lossFalseHairs shed in the shower were already coming out. Wash as often as your scalp needs; daily is fine for an oily scalp.
What to look for5
- ✓For dandruff or itchy flaking: ketoconazole (1 to 2%), zinc pyrithione, selenium sulfide, ciclopirox or salicylic acid.
- ✓Rotate two anti-dandruff actives if one stops working.
- ✓Milder, sulfate-free cleansers if your hair is dry, curly, coily or color-treated, or your scalp is sensitive.
- ✓Fragrance-free if you get scalp or neck rashes; fragrance and cocamidopropyl betaine are known allergens.
- ✓A clarifying shampoo occasionally if you use a lot of styling product.
What to skip4
- ×Growth, anti-hair-loss and 'follicle-stimulating' shampoos priced for regrowth; they don't have the evidence.
- ×Biotin, collagen and keratin shampoos for hair growth; they don't reach or feed the follicle.
- ×'Scalp detox' claims; product residue does not cause pattern hair loss.
- ×Paying extra for 'natural' or 'clean' labels, which have no legal meaning.
How to use it3
- →Focus shampoo on the scalp; the lather rinsing through is enough for the lengths.
- →Leave anti-dandruff lather on for 3 to 5 minutes before rinsing.
- →Use anti-dandruff shampoo 2 to 3 times a week for flare-ups, then once a week to keep it controlled.
Take care4
- !Keep medicated shampoos out of the eyes; selenium sulfide can discolor light or chemically treated hair.
- !Coal-tar shampoos can stain and increase sun sensitivity; ask a clinician before using them on children or in pregnancy.
- !See a dermatologist for sudden or patchy hair loss, a painful, red or scaly scalp, or flaking that doesn't respond to anti-dandruff shampoo within a few weeks.
- !A rash on the scalp edges, neck or ears after a new product may be contact allergy; stop it and consider patch testing.
The studies1 cited · checked against PubMed
Topical antifungals for seborrhoeic dermatitis ↗Okokon EO, Verbeek JH, Ruotsalainen JH, Ojo OA, Bakhoya VN · Cochrane Database of Systematic Reviews · 2015Systematic review and meta-analysis
51 trials with 9,052 people. Topical ketoconazole 2% cut the risk of failed clearance by 31% versus placebo at four weeks, and ciclopirox 1% also beat placebo. Evidence was low to moderate quality, few trials lasted longer than four weeks, and about half had industry ties.