Yeast infections are caused Candida albicans bacteria. These bacteria are known to thrive in warm, moist, tightly covered areas such as the folds of the skin. The most common cause of a yeast diaper rash is antibiotics. Antibiotics prescribed for a bacterial condition will kill the offending bacteria, but also attack the body’s good bacteria. The best way to prevent a yeast diaper rash is to make sure that your baby’s diaper area is clean and dry and follow your pediatrician’s recommendations for treating the yeast diaper rash.