Neck rashes are very common in young babies because they have lots of little folds of skin that rub together, creating heat and friction and trapping sweat. This chafing irritates the skin and sometimes allows yeast to thrive. Since the rash is spreading, it should be reevaluated by a pediatrician or dermatologist. If it is a yeast infection, the doctor will most likely prescribe a stronger anti-fungal or anti-yeast cream, which usually clears things up pretty quickly.
But we suspect that something else could be going on here. Your baby could have eczema (which looks like a red rash with thick, rough patches) or heat rash (which often looks red and spotty). If either of these conditions is to blame, then your baby will need a different treatment (like a hydrocortisone or topical steroid cream), which may explain why the rash hasn't gone away yet.
Once you've seen a doctor and have the rash under control, you can keep it from returning by wiping the area a few times a day with a warm, damp washcloth and dabbing a little A+D ointment on your baby's neck to guard against chafing. While this can help, you should also know that some babies' necks remain prone to rashes until they can consistently sit up and stretch out their necks (usually after 6 months).
Copyright 2009 Meredith Corporation.