Dermatologists advise that daily protection with sunblock should begin at six months of age, and most sunblock products state on the label that they are not to be used by infants under six months of age. But according to both the American Academy of Dermatology (AAD) and the American Academy of Pediatrics (AAP), that rule is not absolute.

In the summer of 1999, the AAP issued a new recommendation which stated that "when adequate clothing and shade are not available, parents can apply a minimal amount of sunscreen to small areas, such as the infant's face and the back of the hands." (Tops of the ears and back of the neck are also a good idea.)

You should check with your pediatrician before using sunblock on the littlest infants, but here are some guidelines for choosing a safe product and using it wisely:

Apply just to exposed areas. There's no need to cover a baby's whole body with sunblock if she's properly dressed... in fact, it could be harmful. Infants don't perspire as efficiently as adults, and covering too much baby skin with sunblock could interfere with the body's cooling mechanism. Cover only exposed areas such as face and hands.

Choose a broad-spectrum sunblock. (Meaning that it blocks both UVA and UVB rays) with a SPF of at least 25. Broad-spectrum products contain one of three active ingredients: avobenzone (trade name: Parsol 1789), zinc oxide, and titanium dioxide. Avobenzone is a chemical sunblock, while zinc and titanium dioxide are physical sunblocks. While both have been tested for safety on baby's skin, some pediatricians recommend that children under six months use a physical sunblock, as it may be less irritating.

Do a "patch test" on your baby before relying on the product. Cover a small (quarter-size) area of skin with the sunblock, and wait a day or two to see if there's any irritation.

Apply the sunblock at least half an hour before sun exposure, to allow the skin to absorb the product.

Choose a waterproof or water-resistant formula, and reapply at least every two hours while babies are outdoors.