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Personal care · product guide

Shampoo: does it work?

Cleans scalp and hair. Anti-dandruff actives have real evidence; 'growth', 'thickening' and 'detox' claims mostly don't.

Moderate evidenceReviewed September 2026

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 evidence?

Moderate evidence

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 see, checked

Anti-dandruff shampoo controls flaking

Holds up

Ketoconazole and ciclopirox beat placebo in trials; zinc pyrithione and selenium sulfide are also established actives.

Shampoo can regrow hair

Unproven

Growth claims rest on ingredients without controlled evidence. Topical minoxidil is the non-prescription product with trials.

'Thickening' shampoo makes hair fuller

Mixed

Coating polymers can make strands look fuller; it's cosmetic and washes out, not regrowth.

Sulfates damage hair or are toxic

Mixed

Strong 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 loss

False

Hairs 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 for

  • 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 skip

  • 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 it

  • 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.

Who should be careful

  • 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 studies

Every citation is checked against its PubMed record.

  1. Topical antifungals for seborrhoeic dermatitis
    Okokon EO, Verbeek JH, Ruotsalainen JH, Ojo OA, Bakhoya VN · Cochrane Database of Systematic Reviews · 2015 · Systematic 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.