Unlike medicines, which are regulated by the Food & Drug Administration, over-the-counter supplements are subject to little oversight. There is no guarantee that their claims or ingredients are backed by science (or that the ingredients on the label are actually even in the tablet) – making the supplement aisle the wild west of every pharmacy. While no vitamin or supplement should ever be taken without consulting a physician first, there are a few that are backed by scientific research showing that they may have a positive effect on our strands, skin, or nails. Here are some of them.

For skin cancer prevention: Vitamin B3, also called nicotinamide, has been shown to lower the risk of nonmelanoma skin cancers (such as basal cell carcinoma or squamous cell carcinoma) and precancerous growths (called actinic keratoses). In a 2015 New England Journal of Medicine study of more than 600 patients with a history of skin cancer, 500mg of B3 taken twice daily led to a 23% drop in new cancerous growths over 1 year. Sun protection remains the most important way to lower skin cancer risk – but those stats aren’t too shabby, for a vitamin.

For brittle nails: Biotin (also called vitamin H or B7) was shown to increase nail plate thickness by 25% in patients with brittle nails, while reducing splitting and improving nail smoothness, according to studies from the Journal of the American Academy of Dermatology (JAAD) and Cutis. The optimal dose isn’t known, but dermatologists have suggested 2.5mg daily for those with delicate nails. Just be sure to let your doctor know if you take biotin, and consider holding off on the vitamin prior to any bloodwork: In 2017, the FDA issued a warning that it can interfere with certain lab tests, including some measuring cardiovascular and thyroid levels.

For thinning hair: As a dermatologist, I never used to recommend dietary supplements for patients with sparse or shedding hair, unless there was a specific nutritional or medical issue to correct. Now I sometimes do for patients with male or female pattern hair loss – the gradual thinning many of us are prone to later in life. Small, randomized, double-blind, placebo-controlled studies of men and women with thinning hair, published in the Journal of Cosmetic Dermatology and Dermatology Research and Practice, showed a significant increase in hair density with reduced shedding over 3 to 6 months on a marine supplement called Viviscal. And the plant-based Nutrafol led to an increased number of hairs, with increased thickness, volume and growth rate in women over 3 to 6 months, according to a May 2018 study from the Journal of Drugs in Dermatology. This supplement contains ingredients said to reduce inflammation, antioxidants to help guard against cell-damage, and saw palmetto, which may inhibit hormonal factors that can contribute to hair thinning.

For psoriasis: Fish oil supplements may help to alleviate rashes in those suffering from psoriasis – a chronic condition of scaly, pink skin that often affects the elbows, knees, scalp, and other areas. A 2014 meta-analysis published in JAAD showed a moderate benefit in psoriasis – reduced area of rash, and improved thickness and redness of psoriasis – after supplementing with omega-3 polyunsaturated fatty acids from fish oils (eicosapentanoic acid, EPA, and docosahexanoic acid, DHA). The study authors suggested doses of 0.45 to 13.5 grams of EPA and up to 9 grams of DHA daily – and explained that the supplements are expected to be most helpful when used along with established psoriasis medications.

For whatever ails you: If there’s a supplement you believe in, it might just work – due to the powerful placebo effect. Decades of research have shown that the expectation of results is sometimes enough to actually see results. That’s one reason I don’t discourage vitamins that have a decent safety profile, if a patient truly believes in them.

But before starting any supplement, be sure to talk to your doctor to find out if it’s right for you and whether it’s safe to take with other medicines.