Viral UV Stickers Claim to Predict When You Should Reapply Your Sunscreen

“If you apply the spot to your upper arm, but you are in a position where your back is getting more direct sunlight,” says Loretta Ciraldo, MD, a board-certified dermatologist based in Miami. 
“Or, if your arm is somewhat shaded and your lower legs aren’t, you may get a false sense of confidence that all of your body is being protected, and you don’t have to reapply SPF when some areas need it to be reapplied.” 

You’ll need to strategically place your spot based on sun exposure and practice other sun-care basics, like wearing protective clothing. That said, “you should avoid hairy or oily areas where the adhesive may not work as well,” notes Jessie Cheung, MD, a New York City board-certified dermatologist.

Next, cover your body and the sticker with your SPF (both mineral and chemical formulas are compatible for use) and wait 30 seconds for it to be fully absorbed. The sticker registers the sunscreen application and will turn clear — this is how you know it’s working. The spot will turn purple when it’s time for you to reapply, and the brand says each sticker lasts a full day and through multiple applications of sunscreen. 

If you’ve got sensitive skin, though, you might want to give one a test run indoors first as “the medical adhesive can cause a contact allergy for people sensitive to certain glues,” Dr. Cheung warns. Additionally, don’t wear the sticker longer than the recommended time, and remove it at the first sign of irritation.

So, do UV stickers actually work?

In short — they can, but they shouldn’t be used as your sole sun-care protection. Sunscreen reapplication should happen every two hours and equal about a shot glass of sunscreen to each exposed area. About 25 percent of people apply the proper amount of sunscreen, so these stickers can be a very helpful reminder of how often people need ​​to reapply to be protected fully.

Since these spots were created and designed to measure the effectiveness of your sunscreen against damaging UVA and UVB sun rays, they deliver as promised on on sunny days. “But on rainy, cloudy days when there isn’t a lot of UV light, they could stay purple and let people think they’re protected, when in reality, sunburn is still possible since UV lights penetrate clouds,” says Roberta Del Campo, MD, a board-certified dermatologist in Miami.