Whether it’s pink pimples on a newborn’s cheeks or fire-engine-red welts on a feverish toddler, a child’s first rash can alarm even the most zen of parents. But bumps and blotches are simply our skin’s way of reacting to certain irritants, infections or hormonal changes, and generally are not a cause for alarm. “Because their immune systems are still developing, young children are more sensitive to chemicals, viruses and bugs than we are,” says Albert Yan, M.D., chief of pediatric dermatology at Children’s Hospital of Philadelphia. “As a result, there are hundreds of different rashes they can get.”

While inflamed and itchy skin can be annoying, most rashes are harmless and will fade on their own. There are some rashes, though, like eczema, that can cause ongoing discomfort unless treated with medication. Others, like impetigo, a skin Infection, are contagious. The following is a field guide to common rashes. Because it can be difficult to distinguish one type from another, it’s a good idea to check in with a pediatrician or pediatric dermatologist when your child’s skin flares up. If a rash is accompanied by tightening of the throat, trouble breathing, or a fever (over 100.4 for an infant or over 101.3 for an older child), be sure to see a doctor right away.