The substance that best promotes healthy growth of skin, hair and nails is GLA (gamma-linolenic acid), which is very hard to come by in the diet. The best sources are evening primrose oil, black currant oil and borage oil, taken in capsules as dietary supplements. Products differ in the amount of GLA they supply and in cost. I usually recommend taking 500 milligrams of black currant oil twice a day, as it's the most economical form. Don't expect overnight results. Maximum improvement occurs after six to eight weeks of use. You may also find that increasing your intake of omega-3 fatty acids by eating more salmon, mackerel, sardines or walnuts or taking fish-oil capsules can help.
To promote healthy skin, use a sunscreen or sun-protective clothing whenever you're outdoors in the sun, not just at the beach. Dermatologists recommend applying sunscreen daily (and reapplying if you swim or perspire heavily). Sun exposure can damage the skin and cause it to age prematurely.
To soften dry skin, the American Academy of Dermatology suggests soaking in the tub for 25 minutes without using soap. Before you get out of the tub, use a moisturizing bath bar. Then pat yourself dry and apply a moisturizing cream or lotion all over your skin. The cream will help prevent dryness by sealing in the moisture from your bath.
As for your hair, dermatologists recommend conditioners containing hydrolyzed proteins or hydrolyzed human hair keratin proteins. They replenish nutrients in the hair shaft and keep hair strands flexible.
To strengthen nails, keep them short, square-shaped, and slightly rounded on top. Use a moisturizer every time you wash your hands, and wear cotton-lined rubber gloves whenever you do chores that involve putting your hands in water. In addition, avoid nail hardeners or polishes containing formaldehyde, which can irritate the skin surrounding the nails. If you polish your nails, choose a hypoallergenic or water-based brand such as Aquarella (www.acquarellapolish.com), and use polish remover with a nonirritating (non-acetone) solvent.
Dry hair and skin and brittle nails can be signs of an underactive thyroid. Simple blood tests can assess your thyroid function. If it is low, your doctor can prescribe thyroid hormones (preferably a brand such as Thyrolar, which supplies both of the hormones produced by the gland).
Andrew Weil, M.D.