Plastic used on some disposable diapers can aggravate diaper rash because babies tend to sweat more with plastic. If you are using this type of diaper, switch to cloth diapers, and dab some baby powder on it before putting on your baby. A cream with zinc oxide, which has anti-inflammatory properties, can also act as a block between the skin and the diaper.
It is also wise to let his nappy area air-dry for a few minutes after washing. Applying a vitamin A and D ointment is also recommended.