Mineral hair sunscreens contain active ingredients like zinc oxide or titanium dioxide that form a protective layer around each strand of hair, and these formulations could leave a white cast on your hair, Saedi says. Chemical hair sunscreens, on the other hand, contain active ingredients like avobenzone that absorb and diffuse the UV rays from the sun, preventing damage. 

While there’s no significant research on the effectiveness of hair sunscreens, they can be a helpful way to prevent the sun from damaging hair. More importantly, they provide protection for your scalp. “I personally like the hair sunscreens that are made specifically for your hair and scalp,” Saedi says, since these are formulated to protect not just your hair, but your skin as well. More on this later.

Hair sunscreen can be helpful for anyone, regardless of hair color, length, or thickness. However, it may be especially beneficial for some. “Lighter hair and thinner hair are more prone to sun damage,” Saedi says, as light hair doesn’t have as much naturally protective pigment, and thinner hair doesn’t provide as much cover for the scalp.

How to Apply Hair Sunscreen
Ensure maximum UV protection with the following hair sunscreen application tips:

Apply every two hours. “Hair sunscreen should always be applied if you are going to be exposed to the sun for an extended period during peak UV time, about 10 a.m. to 3 p.m.,” Dr. Palep says. Just as with regular sunscreen, Saedi recommends reapplying hair sunscreen every two hours. 
Consider the SPF rating. The sun protection factor (SPF) number that you see on regular sunscreen applies to hair sunscreen as well, Saedi says. Higher numbers result in stronger and longer protection. If you have light or thin hair or are in the sun for a long time, you might want to consider a higher SPF (like SPF 50), although there’s no recommended minimum number for hair sunscreen.[2]
Use on dry hair. Most hair sunscreen products are meant for dry hair, so don’t apply them while your hair is wet unless the package directions tell you otherwise.
Coat your strands. Hair sunscreen works by coating the hair cuticle, Palep says, so it’s important to apply from root to tip. If you’re using a spray, use it liberally to coat the outer layer of your hair. If you’re using a mousse or powder, use your hands to rub it everywhere.
Don’t forget your scalp. Because many hair sunscreens are formulated for your hair and scalp, it’s important to coat the skin, too.
Reapply after you get wet. “Sunscreens are not waterproof, but they are water resistant,” Saedi says. “If you are going swimming, it needs to be reapplied more frequently — the same applies to sunscreen on your body.” After swimming, mist or massage another coat of sunscreen onto your hair and scalp.
How Can I Protect My Scalp From Sun Damage?
While damaged hair is an annoying side effect of sun exposure, Palep says you should be more concerned about the damage that UV rays can do to your scalp. 

The darker and thicker your hair, the more protection your scalp has.[3] But exposed skin (like the skin on your part or the skin under thinner or lighter hair) can still get burned, which poses the same risks as sunburn on any other part of your body. Sunburns are not only painful, but they also quicken skin aging and are a leading cause of skin cancer.[4] Roughly 13 percent of tumors are on the scalp, per research.[5]
Applying scalp and hair sunscreen can help protect against these effects, Saedi says. She also recommends wearing a hat — preferably a wide-brimmed one, which will protect your entire scalp as well as your hair — or a headscarf, especially if you’ll be in the sun for an extended period or you don’t want to use hair sunscreen. Hats and headscarves provide a physical barrier to protect your hair and skin and won’t wash or wear off like hair sunscreen.

The Takeaway
The sun’s UV rays damage the hair cuticle and the protein (keratin) that gives hair its structure. In addition, the delicate skin of the scalp is susceptible to sunburn and damage, accelerating skin aging and increasing skin cancer risk. Using hair sunscreen with a hat or headscarf offers the best protection.