Scleroderma is a long term autoimmune disease that results in hardening of the skin. In the more severe form, it also affects internal organs. The cause is unknown. The underlying mechanism involves the body's immune system attacking healthy tissues. There is a strong association with certain mutations in HLA genes. Environmental factors have also been implicated.There are two main types of the disease: the localized form (called localized scleroderma, limited scleroderma, or morphea) and the systemic form (called systemic scleroderma, diffuse scleroderma, generalized scleroderma, or systemic sclerosis). Limited scleroderma involves mainly the skin of the hands, arms and face. Diffuse scleroderma is rapidly progressing and affects a large area of the skin and one or more internal organs, frequently the kidneys, esophagus, heart and/or lungs. This form of scleroderma can be quite disabling. A limited cutaneous subtype of it is called CREST syndrome.