When it comes to your baby's skin, you can depend on one thing: It's bound to erupt into a rash during the first year. Why? The human skin acts as a protective barrier against all sorts of elements, from sun to bacteria, but it takes about a year for that epidermis to get up to speed and function effectively, says Bernard Cohen, M.D., director of pediatric dermatology at Johns Hopkins Children's Center. It starts out thinner, has less pigment, and doesn't regulate temperature as well as the skin of bigger kids and adults. Of course, no baby escapes the most common skin issue--diaper rash. The diaper area is warm and moist, which breaks down the skin on that tender tush. Add irritating poop and pee and you've got the perfect environment for breakouts. Keep diaper rash under control by changing your baby often, using petroleum jelly or a barrier cream with zinc oxide to protect his bum, and letting his naked bottom air out occasionally (put a sheet on the floor and let him loose). Protect the rest of that fragile birthday suit with mild products, such as hypoallergenic and fragrance-free soaps, washes, and lotions. Once your baby turns 1, you can relax a little--his skin will be thicker and more rash-proof.