Tissue hardening, also known as sclerosis, is a medical condition in which the tissue of an organ or other body part becomes hardened and loses its elasticity. It is caused by the accumulation of collagen fibers in the affected area, leading to a decrease in the flexibility of the tissue. Sclerosis can affect any part of the body, including the skin, muscles, tendons, ligaments, and organs. It is most commonly seen in the elderly, but can also occur in younger individuals. Treatment for tissue hardening depends on the severity of the condition and may include physical therapy, medications, and lifestyle changes.