Tea tree oil: acne, athlete's foot, dandruff and why it must never be swallowed

Tea tree oil is steam-distilled from Melaleuca alternifolia leaves. It is not the same as the tea you drink, and the name is a coincidence. Pure oil is highly concentrated, and many shop products are dilute gels, shampoos and creams. Undiluted oil on skin is a common cause of reactions, so the strength on the label matters.

Limited research suggests that tea tree oil applied to the skin might help acne, and more studies are needed. It is not a replacement for established treatments. The linked acne guides describe topical retinoids, benzoyl peroxide, antibiotics, hormonal options and isotretinoin, chosen by severity. Skin that is scarring, painful and nodular, or acne that is affecting mood, should be reviewed by a GP or dermatologist rather than treated with oils indefinitely.

For athlete's foot, limited research suggests tea tree oil might be helpful, but it may not work as well as standard treatments. The NHS describes over-the-counter antifungal creams, sprays and powders from a pharmacy, which usually take a few weeks to work. Keeping feet clean and dry between the toes, wearing fresh cotton socks daily and not wearing the same shoes for more than two or three days in a row all help.

Evidence for fungal nail infection is insufficient to draw conclusions, and nails often need prescribed treatment. A foot that becomes hot, painful and red suggests secondary infection and needs same-day medical advice, as does any foot problem in someone with diabetes or a weakened immune system.

• See a GP if pharmacy treatment fails, if there is significant pain or spreading infection, or if you have diabetes.

• A GP may take a skin scraping, or prescribe antifungal tablets for persistent cases.

Tea tree oil is also promoted for head lice, eyelid inflammation, gum disease and dental plaque. The NCCIH says evidence for these uses is lacking. Eyelid products and mouthwashes need particular care, since the eye and mouth are sensitive and swallowing is a risk with a mouth rinse.

Tea tree oil should not be swallowed. Taken by mouth it can cause serious symptoms such as confusion, unsteadiness, inability to walk and coma. Keep bottles out of reach of children, who are the most frequent victims of accidental ingestion, and store them tightly closed. If someone has swallowed it, contact NHS 111 or call 999 if they are drowsy, confused or unsteady.

Most people tolerate it on the skin, but some get redness and irritation. Oil that is old, or has been exposed to heat, light or air, appears more likely to provoke reactions, so store it in a dark bottle in a cool place and discard it when it smells off. Testing a diluted drop on the inner forearm first is a sensible habit.

Topical tea tree products appear safe in pregnancy and breastfeeding, though talking to a midwife or pharmacist is advisable. The NHS does not recommend herbal medicines for children given the lack of safety data, so ask a pharmacist before applying any essential oil to a child. Oils used in diffusers or on bedding can also be hazardous to pets, so check with a vet.

In the UK, most tea tree oil products are cosmetics or toiletries and are not licensed medicines. The MHRA has observed that most herbal products are unlicensed and standards vary widely. A pack making treatment claims for a disease is a sign to be cautious.