The best way to prevent excessive moisture in your baby's diaper is to change diapers frequently. By keeping your baby's diaper area as clean as possible, you'll be helping your baby avoid getting a rash that isn't easy to get rid of.
Change the baby's diaper as soon as you realize it's soiled. This will keep the urine and feces in the diaper from coming into prolonged contact with your baby's delicate skin. When your baby is breastfed, the solid waste isn't very problematic. However, when babies begin to eat solid foods, not only does the waste become harder on your nose, but bacteria and other organisms in the stool (such as digestive enzymes) can invade skin that has been weakened by exposure to moisture. A new addition to your baby's diet may also cause diarrhea, which is even more likely to cause diaper rash.
Urine contributes to diaper rash in a number of ways. First, the moisture itself leads to weakening and tiny abrasions in the skin. Second, urine is acidic, and this too will damage an area of skin. Finally, when urine is left in contact with feces, bacteria from the feces begins to break down the urea, producing ammonia. Ammonia has no effect on unblemished skin, but if there's a breach in the skin, then ammonia causes further damage.