The major muscle in the chest is the pectoralis major. This large fan-shaped muscle stretches from the armpit up to the collarbone and down across the lower chest region on both sides of the chest. The two sides connect at the sternum, or breastbone. This muscle moves each shoulder joint in four distinct ways as well as keeps the arms attached to the body.
Women and men both have breasts, but women have more breast tissue than men. The breasts contain mammary glands. Only the mammary glands in women can make milk to feed a baby.
Some women may experience a sharp pain under their right breast that comes and goes. Others may experience it every time they take a breath. Sometimes this pain radiates into the back, armpit, or up to the breastbone.