Menstruation, also known as a period or monthly, is the regular discharge of blood and mucosal tissue from the inner lining of the uterus through the vagina. Up to 80% of women report having some symptoms prior to menstruation. Common symptoms include acne, tender breasts, bloating, feeling tired, irritability, and mood changes. These symptoms interfere with normal life, and therefore qualify as premenstrual syndrome, in 20 to 30% of women. In 3 to 8%, symptoms are severe.