Relaxin: A hormone produced during pregnancy that facilitates the birth process by causing a softening and lengthening of the cervix and the pubic symphysis (the place where the pubic bones come together). Relaxin also inhibits contractions of the uterus and may play a role in timing of delivery. Relaxin works by simultaneously cutting collagen production and increasing collagen breakdown.

A synthetic form of relaxin has been reported to be useful in treating scleroderma (a connective tissue disease that causes the skin to become tight and thick), improving the skin condition, mobility, and function.