Yeast normally lives harmlessly on and in the body. It's found on the skin, in the digestive system (including the mouth and throat), and in the genital area. But it can cause an infection in certain conditions. This can happen when the skin is damaged, when it's warm and humid, or when a child has a weak immune system. In some very sick children, it can infect deeper tissues or the bloodstream and cause serious illness. Antibiotics can also cause the yeast to overgrow. This is because antibiotics kill normal bacteria that usually prevent too much yeast from growing. Treatment with other medicines, such as corticosteroids, may also promote candidiasis.