Erections start in the brain. When sights, sounds, smells, sensations, or thoughts make a man sexually aroused, his central nervous system signals the arteries in his penis to relax.

The blood flow to his penis increases to 16 times the normal level, the veins that carry blood away from the penis are effectively blocked, and an erection is born. This extra blood stays in the penis as long as the man remains aroused or until he ejaculates.

Erections start in the brain. When sights, sounds, smells, sensations, or thoughts make a man sexually aroused, his central nervous system signals the arteries in his penis to relax.

The blood flow to his penis increases to 16 times the normal level, the veins that carry blood away from the penis are effectively blocked, and an erection is born. This extra blood stays in the penis as long as the man remains aroused or until he ejaculates.

But sometimes, there’s a breakdown in the process. If the brain doesn’t send the right signals, if the nerves that pass the signals from the brain to the penis are damaged, or if the arteries can’t respond to those signals, a man will be unable to have an erection.

Contrary to popular belief, erectile dysfunction - sometimes called impotence - is not inevitable with age (although it is more common in older men). And although the mind can play a major role in sexual function and desire, most erectile problems have an underlying physical cause. But worrying about the condition will definitely exacerbate it, setting off a cycle of “performance anxiety” that only makes the problem worse, so it’s important to seek help.

Many things can interfere with one or more of the steps necessary to achieve an erection, but medically speaking, it usually boils down to a problem of blood flow. If you suffer from erectile dysfunction, one of the following factors is probably to blame:

  * Cardiovascular disease. High blood pressure, atherosclerosis (narrowing or “hardening” of the arteries), and other disorders of the heart and blood vessels can hamper the flow of blood to the penis.

  * Medications. Many commonly used drugs can short-circuit the process that leads to erections by interrupting nerve impulses or blood flow to the penis. Some examples: antihistamines, antidepressants, tranquilizers, appetite suppressants, cimetidine (an ulcer drug), and blood pressure medications such as beta blockers and diuretics. If you develop erection difficulties while taking antidepressants or blood pressure medicines, remember that the conditions you’re taking the medicines to remedy could also be partly to blame, so stopping them isn’t necessarily the answer. Always get your doctor’s advice before you stop taking any prescription medicine.

  * Diabetes. Because this disease can damage nerves that control blood flow and blood vessels themselves, blood flow to the penis can be impaired.

  * Prostate surgery. Not long ago, almost all men had problems achieving erections after undergoing surgery for prostate cancer. Such problems are still a common side effect of prostate surgery, as well as radiation treatment for prostate or colorectal cancer. But new surgical techniques can often spare the nerves that supply the penis, so sexual function need not be a problem for these patients.

  * Smoking. Cigarette smoking constricts and damages blood vessels, reducing blood flow to the penis. Research suggests that men who smoke and have other health problems, such as heart disease, are more likely to have trouble with erections.

  * Psychological factors. It’s no secret that relationship problems have a direct effect on a couple’s sex life. Feelings of resentment or hostility - harbored by either partner - can derail intimacy. And stress, anxiety, guilt feelings, depression, and low self-esteem can all trigger or compound erectile dysfunction. (Anxiety, after all, has a direct physical effect: It makes the brain release chemicals that constrict the smooth muscles and blood vessels around the penis, limiting blood flow.)

  * Other factors. Alcoholism, pelvic injuries (such as fractures), damage to the nerves that control blood flow to the penis, multiple sclerosis, and below-normal levels of testosterone can all lead to erectile dysfunction.

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American Urological Association