Epididymitis is an infection or irritation of the epididymis—the coiled tube that sits behind each testicle. It usually starts on one side and builds fast, turning a normal day into a careful waddle. The first sign is a deep, throbbing ache at the back of the ball. It feels like someone flicked you hours ago, but the throb keeps growing. Red, shiny skin follows. The scrotum on the sore side turns lobster-colored and feels warmer than the other half. Swelling balloons the sac. The epididymis feels like a thick, tender cord, and the testicle may seem to ride higher or... Learn more