It's upsetting to see any rash or bump on your baby's perfect skin, but chafing rashes are very common in babies and usually heal quickly. Most chafing rashes in babies appear in the diaper area and are caused by the diaper rubbing against your baby's skin, sensitivities to chemicals in disposable diapers, detergents used on cloth diapers or a reaction to a diaper cream. A few changes to your diaper routine should clear up the rash quickly and help your baby's skin stay healthy.
Leave your baby diaperless as often as possible to allow the skin to breathe and to help heal the rash. If your baby is not mobile yet, simply lay him on a towel or on top of an open diaper, and switch the layer underneath him for a fresh one when necessary. Even a few minutes of diaperless time every day will help his skin recover more quickly.
Try a different type of diaper. If you are using disposable diapers, try a different brand -- preferably one with fewer chemicals -- or switch to cloth diapers to see if that helps. If you are using cloth, make sure you are using a detergent that is recommended by the manufacturer and that you are washing in hot water. If you are using cloth diapers with a microfleece or similar wicking layer of material against your baby's skin, try switching to plain cotton diapers. Use breathable covers such as PUL fabric or wool, not plastic or rubber.
Change her diaper frequently -- every time it's wet, if possible. Always change the diaper immediately when it is soiled.
Clean your baby well every time you change his diaper. Use plain water or wipes with no fragrances or additives to avoid chafing from chemical sensitivities.
Use diaper rash cream to create a protective layer between the diaper and your baby's skin. If you suspect a chemical sensitivity, then try different creams to make sure the cream isn't causing the rash.
Fasten the diaper loosely to allow extra air flow against your baby's skin even when she is wearing a diaper.