What hair and scalp ingredients actually do
From medicated actives such as ketoconazole and coal tar to everyday silicones, sulfates and oils: what each is for, the cautions, and how strong the evidence really is.
How we rate the evidence
- Evidence: StrongLicensed medicine or consistent good-quality trials for this use.
- Evidence: ModerateSome good evidence, but not for every claim or every person.
- Evidence: LimitedSmall or early studies only — promising at best.
- Evidence: CosmeticChanges how hair looks or feels; not a treatment for any condition.
Ketoconazole
Antifungal medicine in shampoos for dandruff and seborrhoeic dermatitis
Evidence: Strong CosmeticPiroctone olamine
Anti-dandruff ingredient now common in UK supermarket shampoos
Evidence: Limited CosmeticZinc pyrithione
Former anti-dandruff staple — banned from cosmetics in Great Britain since October 2022
Evidence: Limited Medicine & cosmeticSalicylic acid
Loosens and lifts scale in anti-dandruff shampoos and scalp treatments
Evidence: Limited Medicine activeCoal tar
Long-established medicine for scaling in dandruff, seborrhoeic dermatitis and mild scalp psoriasis
Evidence: Limited Medicine & cosmeticSelenium sulfide
Anti-dandruff ingredient that targets the yeast linked to flaking
Evidence: Limited Medicine activeMinoxidil
Over-the-counter lotion or foam for male and female pattern hair loss
Evidence: Strong Medicine & cosmeticDimeticone (for head lice)
Silicone in pharmacy head lice lotions and sprays that kills lice physically, not as a nerve poison
Evidence: Strong CosmeticSilicones
Smoothing, detangling and shine in conditioners, serums and heat protectants
Evidence: Cosmetic CosmeticSulfates (SLS and SLES)
The main cleansing and foaming detergents in most shampoos
Evidence: Cosmetic CosmeticGlycerin
Humectant that helps products hold water; adds slip and softness
Evidence: Cosmetic CosmeticProteins (hydrolysed keratin, wheat, silk…)
Conditioning and temporary "repair" for damaged or bleached hair
Evidence: Cosmetic CosmeticOils (coconut, argan, olive, mineral)
Pre-wash treatments, shine and softness — and descaling in some medicines
Evidence: Cosmetic CosmeticRosemary oil
Popular "hair growth" oil — backed by one small trial, not a proven treatment
Evidence: Limited CosmeticCaffeine
Marketed against hair thinning; evidence is mostly lab-based or company-funded
Evidence: LimitedNot medical advice. This guide is general information from the sources listed, not a diagnosis or a substitute for a pharmacist, GP or dermatologist. Medicines such as ketoconazole, coal tar and minoxidil come with a patient leaflet: read it, and ask a pharmacist if you are unsure. If you are worried, or symptoms are severe or not improving, get advice. Read our health information policy.