A hemangioma, also known as infantile hemangioma (IH), is one of the most common benign tumors of infancy and occurs in approximately 510% of infants, though it occurs past infancy on rare occasions. Infantile hemangiomas are benign vascular tumors composed of an increased number of unique endothelial cells that line blood vessels. They occur more frequently in female, premature and low birth weight infants. Infantile hemangiomas usually appear within the first weeks of life and grow most rapidly during the first three to six months of life. For most hemangiomas, 80% of infantile hemangioma size is generally reached by 3 months of age. Usually, growth and proliferation is complete and involution commences by twelve months of age. However, involution occurs slowly over many years with a majority of infantile hemangioma regression occurring by five years of age. Although infantile hemangiomas spontaneously regress over time, some may leave residual redundant fibrofatty tissue, scar, residual telangiectasia, or pigmentary changes. The word "hemangioma" comes from the Greek haema- (), "blood"; angeio (), "vessel"; -oma (-), "tumor".