The Human Body

Excitement Stage

The excitement stage of sexual arousal is characterized by increased blood flow to blood vessels (vasocongestion), which causes tissues to swell. In men, the tissues in the penis become engorged with blood, causing the penis to become larger and erect. The skin of the scrotum thickens, tension increases in the scrotal sac, and the scrotum is pulled up closer to the body. Men may also experience nipple erection.

In women, vasocongestion occurs in the tissue surrounding the vagina, causing fluids to seep through the vaginal walls to produce vaginal lubrication. In a process similar to male erection, the glans of the clitoris becomes larger and harder than usual. Muscular contraction around the nipples causes them to become erect. However, as the excitement phase continues, vasocongestion causes the breasts to enlarge slightly so that sometimes the nipples may not appear erect. Vasocongestion also causes the labia majora to flatten and spread apart somewhat and the labia minora to swell and open. The upper two-thirds of the vagina expands in a “ballooning” response in which the cervix and the uterus pull up, helping to accommodate the penis during sexual intercourse.

Both women and men may develop “sex flush” during this or later stages of the sexual response cycle, although this reaction appears to be more common among women. Sex flush usually starts on the upper abdomen and spreads to the chest, resembling measles. In addition, pulse rate and blood pressure increase during the excitement phase.