As the hemangioma grows the skin can not keep up. The elasticity of the skin is reduced, it then splits and opens. This causes ulceration. Because the skin over a hemangioma is compromised it is not unusual for it to split after just a slight bump. Since the hemangioma is growing faster then the skin, the skin can not repair itself, healing may not occur for months.
Ulcerated hemangiomas are a great risk for infection.
Perianal and urogenital lesions are at an increased risk for infection because of urine and feces. Even the most careful diapering can't prevent infection. Once ulcerated all hemangiomas become painful. In the presence of a wet or soiled diaper this pain can be exasperating. Cleaning the area becomes more difficult and thus the risk of infection becomes greater.