No guessing, no forgetting! These color-changing wristbands alert you when it's time to reapply sunscreen or even seek shade. Each time during the day that you cover your child with sunscreen, just coat the UV wristband, too. Adjustable, waterproof, and disposable. Calibrated to work with sunscreens SPF 15 and higher. Sun monitors are sensitive to both UVA and UVB rays. For ages 12 months and up. Activate the sun monitor by exposing to sunlight; it will turn purple. Then, coat it with the same sunscreen you're applying to your child's skin. The wristband turns brown when it's time to reapply sunscreen and turns peach when it's time to get out of the sun. (Turns peach when your child's skin has reached its "mean erythema dose" or MED threshold, which is the amount of sun that causes the initial reddening of the skin.) Recoat the band each time you reapply sunscreen, and then toss at the end of the day Stays on well in water and continues to monitor sun exposure in water