Causes

An overactive muscle causes a testicle to become a retractile testicle. The cremaster muscle is a thin pouch-like muscle in which a testicle rests. When the cremaster muscle contracts, it pulls the testicle up toward the body. The cremaster reflex can be stimulated by rubbing a nerve on the inner thigh and by emotion, such as fear and laughter. The cremaster is also activated by a cold environment.

If the cremaster reflex is strong enough, it can result in a retractile testicle, pulling the testicle out of the scrotum and up into the groin.