No question about it, hair needs to be protected from the sun! Sun damage destroys hair by breaking down the bonds that keep its structure intact. Where brushing and combing chip away at the outer cuticle, energy from the sun destroys the interior of hair, which explains why hair color fades with sun exposure. Yet despite this desperate need for protection, sunscreens in hair-care products such as shampoos, conditioners, and styling products are nothing less than a waste of time and money. Unfortunately, there is no way that these formulations can provide adequate sun protection for the hair because shampoos and conditioners are meant to be rinsed out, and consequently there is no way to know how much, if any, sunscreen remains on the hair. In fact, given the water-solubility of most sunscreens, they are probably rinsed away almost immediately. Creating water-resistant sunscreens is the logical solution, but no one has come up with a version that holds up. Moreover, sunscreen ingredients do not adhere well to hair—what it would take to get those ingredients to cling would make hair feel coated, look greasy, and be almost impossible to style.

Leave-in hair-care products that contain sunscreen are a better bet, but only slightly. Although the sunscreen's ability to stay on the hair shaft increases when it's included in a leave-in product (that isn't rinsed off), sunscreen ingredients degrade or are removed with heat from a blow dryer, flat iron, or curling iron. Even brushing the hair can remove sunscreen from the hair shaft.

Hair-care products are not allowed to have SPF numbers because the FDA does not consider hair-care products with sunscreen safe or reliable for sun protection. And without an SPF number (or even if there is an SPF number, which is illegal), there is no way to determine how long the hair shaft will be protected, or indeed if any sunscreen is left behind at all. If you don't know the SPF, you have no idea if the product is an SPF 2, SPF 8, or SPF 15. Moreover, with the skin we know that sunscreen must be reapplied after swimming or long exposure to the sun, but what about the hair? After two hours of bike riding, are you going to reapply your leave-in conditioner with sunscreen and get your hair gooped up all over again?

I'm not saying that sunscreen ingredients in very controlled situations can't protect hair from sun damage, because they can. There are studies in which a swatch of hair is covered with sunscreen ingredients, then placed under UVA/UVB light, and after a period of time measured for deterioration. The sunscreen ingredients absolutely prevented damage. But that kind of study doesn't reflect how the product is actually used by consumers. Who is going to slather sunscreen on their hair then just leave it, doing nothing else to their hair afterward? Until there is a solution to the application and adherence issues, it is a huge mistake to rely on sunscreen in hair-care products. Until the FDA gives its SPF blessing to hair-care products meant for the hair, not the scalp, wear a hat when spending long periods of time in the sun. That's the only real way to prevent sun damage to your hair.

Sources for the article above: International Journal of Cosmetic Science, June 2006, pages 231-232; Dermatlogic Clinics, January 2006, pages 81-84; Journal of Photochemistry and Photobiology, May 2004, pages 109-117; and Journal of Cosmetic Science Supplement 2004, pages S105-S112).