Expert answer: Patricia Treadwell, pediatric dermatologist
Until August 1999, the American Academy of Pediatrics (AAP) recommended against using any type of sunscreen on babies younger than 6 months because the products hadn't been tested on children that young. But since then the advice has slightly changed. The AAP still says the best way to protect a baby this age from the sun is to keep him or her in the shade of a tree, umbrella, or stroller and dress him or her in long sleeves and a hat. But if that's not possible, it's fine to use a small amount of sunscreen on your baby's face and hands.
I recommend choosing a "physical" sunscreen – one made with zinc oxide or titanium dioxide. Unlike the stuff in chemical sunscreens that the skin absorbs, which may cause irritation or allergic reactions, these ingredients merely sit on top of the skin, forming a barrier against the sun's rays.