Almost every baby will get diaper rash at least once during the first 3 years of life, with the majority of these babies 9-12 months old. This is the time when the baby is still sitting most of the time and is also eating solid foods, which may change the acidity of the bowel movements.

Diaper rash appears on the skin under a diaper. Diaper rash typically occurs in infants and children younger than 2 years, but the rash can also be seen in people who are incontinent or paralyzed.