To take the guesswork out of monitoring your sun exposure, these small stickers indicate when you?ve put on enough sunscreen and when it?s time to reapply it. The medical-grade adhesive ensures each sticker stays in place for up to an entire day, even when you?re swimming. When you apply sunscreen over it and your skin, the absorbent material closely mimics the way skin absorbs and sheds sunscreen. In direct sunlight, the sticker?s UV-reactive dye changes color, becoming clear when you?ve put on enough sunscreen to avoid skin damage, and regaining color as the sunscreen wears off. (The speed of the color change varies with the user?s skin characteristics, sunlight intensity, exposure time and other factors.) Effective with various types of sun protection, it works best with lotion sunscreens with an SPF 30 rating and is approved for use with children ages 3 . Made in the USA, it comes as a pack of 12 stickers