Nothing seems to say "bad mom" like a nasty case of diaper rash. But you can skip this guilt trip. "Some babies are just more prone to it," says Vincent Iannelli, M.D., associate professor of pediatrics at UT Southwestern Medical Center in Dallas, Texas. Breastfed infants, for example, are more likely to develop diaper rash because they have more frequent stools, he notes. Do your best to prevent and treat it, but know that an irritated bottom is a rite of passage for most little ones.If your baby has frequent outbreaks, change her diaper frequently and always apply a rash ointment such as A&D or Desitin as a preventative measure.When his tushie is really sore, avoid baby wipes (they can sting). Use a squirt bottle of water and gentle patting with a washcloth instead. Then apply a coating of a super-moisturizing diaper rash treatment. Two Dr. Iannelli likes: Triple Paste and Boudreaux's Butt Paste.If the rash persists for more than three or four days, or you notice little bright red bumps, call the doctor. Your baby may have developed a yeast infection.