Because an erection requires a precise sequence of events, ED can occur when any of the events is disrupted. The sequence includes nerve impulses in the brain, spinal column, and area around the penis, and response in muscles, fibrous tissues, veins, and arteries in and near the corpora cavernosa.

Damage to nerves, arteries, smooth muscles, and fibrous tissues, often as a result of disease, is the most common cause of ED. Diseases, such as diabetes, high blood pressure, nerve disease or nerve damage, multiple sclerosis, atherosclerosis, and heart disease, account for the majority of ED cases. Patients should be thoroughly evaluated for these conditions before they begin any form of treatment for ED.

Lifestyle choices that contribute to heart disease and vascular problems also raise the risk of ED. Smoking, drinking alcohol excessively, being overweight, and not exercising are possible causes of ED.

Surgery, especially radical prostate and bladder surgery for cancer, can also injure nerves and arteries near the penis, causing ED. Injury to the penis, spinal cord, prostate, bladder, and pelvis can lead to ED by harming nerves, smooth muscles, arteries, and the fibrous tissues of the corpora cavernosa.

In addition, ED can be a side effect of many common medicines such as blood pressure drugs, antihistamines, antidepressants, tranquilizers, appetite suppressants, and cimetidine, an ulcer drug.

Psychological factors such as stress, anxiety, guilt, depression, low self-esteem, and fear of sexual failure can also cause ED. Even when ED has a physical cause, psychological factors may make the condition worse.

Hormonal abnormalities, such as low levels of testosterone, are a less frequent cause of ED.

The devices have three components: a plastic cylinder, into which the penis is placed; a pump, which draws air out of the cylinder; and an elastic ring, which is moved from the end of the cylinder to the base of the penis as the cylinder is removed. The elastic ring maintains the erection during intercourse by preventing blood from flowing back into the body (see Figure 2). The elastic ring can remain in place up to 30 minutes. The ring should be removed after that time to restore normal circulation and to avoid skin irritation.

Couples may find that using a vacuum device requires some practice or adjustment. An erection achieved with a vacuum device may not feel like an erection achieved naturally. The penis may feel cold or numb and have a purple color. Bruising on the shaft of the penis may occur, but the bruises are usually painless and disappear in a few days. Ejaculation may be weakened because the elastic ring blocks some of the semen from traveling through the urethra, but the pleasure of orgasm is usually not affected.

A vacuum device causes an erection by creating a partial vacuum around the penis, which draws blood into the corpora cavernosa.