Scleroderma refers to a group of diseases that involve the abnormal growth of connective tissue, which supports the skin and internal organs. Scleroderma can affect the skin, making it hard and tight; it can also damage the blood vessels and internal organs such as the heart, lungs, and kidneys. Estimates for the number of people in the United States with the systemic (body-wide) form of scleroderma range from 40,000 to 165,000. The number of people with all scleroderma-related disorders is between 250,000 and 992,500.