The best way to treat diaper rashes is to minimize skin irritation and apply a protectant/barrier to help skin heal.

Diaper rashes occur because skin irritation is more likely in warm, moist areas. Irritation is the most common cause of rashes in the genital area. Skin (and baby skin in particular) is easily irritated when it is left in a moist, warm environment. Stool and urine can also be irritants.

Dehydration is a math problem. Dehydration can happen because of illness, over-exertion, or the environment.