Peanut allergies can develop at very young ages, and one of the symptoms of a peanut allergy can, in fact, be a rash or hives. However, it's rare for a food allergy to cause a rash on a baby's bottom (and it's also unusual for infants to be ingesting foods with peanuts or peanut derivatives in them). Generally, diaper rash is the result of friction or irritation. If your baby is sitting in a wet diaper and that diaper is rubbing on his bottom, he'll develop a red, shiny diaper rash. In addition, sitting in urine or feces can cause irritation -- due to the acid content in waste. Occasionally, rashes on babies' behinds are the results of fungal or yeast infections, particularly if the baby is on antibiotics. These rashes are typically raised and patchy; they're normally centered on genitalia.
Food allergies can cause red rings of rash around an infant's anus. But infants' bottoms are more likely to have allergic reactions on contact rather than through food. Baby wipes, diapers, detergent, soap, lotion and plastic pants can all result in allergic rashes. When babies start to eat solids, the introduction of new foods might increase their frequency of diaper rashes. The changes that the new foods bring about in their stool can irritate their bottoms; plus, they may start to go more often. The same effects can be caused by changes to a nursing mother's diet.
The key to preventing diaper rash is to keep your infant's bottom clean and dry. Applying diaper rash cream each time you change your baby's diaper might help avoid future rashes. If you notice a rash that doesn't go away or that appears after your baby eats certain foods, check with your doctor. He can test to see if your baby has a food allergy, contact allergy or some type of infection that needs steroid or antibiotic treatment.