👉 Chamoising is a medical condition that occurs when the skin on your arms, legs, and back becomes thickened. It can be caused by several factors such as aging, genetics, or certain medications. The cause of chamoising varies from person to person, but it's usually associated with an imbalance in the production of collagen, which is a protein found in the skin that helps keep it firm and supple. When this balance is disrupted, the skin can become thickened and irregular.