Babies often get inflammation in skin folds. This is especially common in neck folds and diaper area. See: Intertrigo on Dermnet, for an overview.
Brian Maurer, of Enfield, CT, is a pediatric practitioner. Here is his easy approach for intertrigo in babies.
(1) Cleanse the area 2 or 3 times daily with a mild soap (Dove unscented) and water.
(2) Dry area with a hairdryer on low setting.
(3) Apply a desiccant preparation. Add cornstarch powder to an aluminum hydroxide antacid preparation (e.g. Mylanta, Maalox) to make a paste, which can be dabbed onto the area and allowed to dry. Domeboro solution applied as a wet compress also works well. Allow the area to air dry after application is complete.
(4) Alternatively, if a fungal component is suspected, dust the area with Mycostatin powder. Caution: Take care when applying powder. Shake a small amount onto finger and apply manually. Avoid shaking powder directly onto skin at neck, as the infant might inhale the fine dust and develop a reactive pneumonitis.