What Happens during an Erection?

The penis contains three long cylinders of erectile tissue. Two of the cylinders lie side by side, while the third lies beneath them. The urethra, which is the urine and sperm channel, runs through this lower cylinder. Sexual excitement causes the cylinders to fill with about 100–140 mL of blood and, as they swell, so the penis becomes erect. And as the erectile tissue swells, it squeezes the veins in the penis. These veins normally drain blood away from the penis, so the squeezing action prevents blood flowing away and keeps the penis erect. (Imagine a bath-tub filling with the tap on and a plug in the drain.) After orgasm and ejaculation these events go into reverse, and the penis becomes limp again.

How the System Fails (Impotence)

There are multiple causes of impotence. Now more is known about the blood supply to the penis; it is recognized that physical problems are often responsible. For example, nerves to the spongy tissue can be damaged by diabetes, blood flow can be impaired by atherosclerosis (clogged arteries) and many medications interfere with erections.

Medications and drugs. Many medications and drugs can interfere with erections. Here are some of the most common culprits:

  • cimetidine (for duodenal ulcer)
  • some drugs for high blood pressure (for example, thiazide diuretics especially in high doses, methyldopa, most beta-blockers). Erection problems affect about 1 in 5 men taking beta-blockers (Journal of the American Medical Association 2002;288:351–357)
  • finasteride (for prostate enlargement or baldness)
  • phenothiazines (for some psychiatric conditions)
  • alcohol and marijuana (cannabis)
  • drugs used for prostate cancer (for example, some GnRH analogues and anti-androgens)
  • some antidepressants
  • cholesterol-lowering drugs (probably)
  • non-steroidal anti-inflammatory drugs, also known as NSAIDs (possibly).

Medical conditions. Many medical conditions can cause difficulty with erections by damaging the blood vessels and nerves. Of course, if you have one of these conditions, it does not mean that you will necessarily be impotent. Some of the most important medical conditions that can cause impotence are:

  • diabetes
  • hypertension (high blood pressure)
  • vascular disease (clogged arteries) – linked with smoking
  • severe liver disease
  • thyroid disease
  • neurological conditions (for example, spinal injury, multiple sclerosis)
  • Peyronie’s disease
  • tight foreskin
  • kidney failure.

Cardiovascular disease (clogged or damaged arteries) is one of the most common causes of erection failure. For an erection, you need good blood flow into the penis through its arteries. If the arteries in the penis are clogged or damaged, it is likely that other arteries in the body are in the same state. This includes the coronary arteries, which supply the heart muscle with oxygen and nutrition. If the coronary arteries become furred up, there is an increased risk of angina, heart attack or stroke. Therefore, erection problems can be an early marker for coronary artery disease and may reveal the presence of subclinical (not severe enough to present definite symptoms) coronary artery disease in otherwise asymptomatic men (Sexual Medicine Reviews 2019;7:455–463).

If you tell your doctor that you have erection problems, he or she will recognize this as a warning and will check your cardiovascular system. This will include a blood pressure check and measurement of the lipids in your blood, such as cholesterol. Your blood sugar should also be measured, because diabetes is another risk factor for clogged arteries. Your doctor can then advise you on how to keep your arteries as healthy as possible. If you are a smoker, you must definitely stop (see below) – look at www.quit.org.uk for help. You should lose weight if you are obese, and if your blood lipids are raised your doctor will prescribe a statin medication.

Some prostate operations (especially radical prostatectomy) can also cause impotence.

Ageing. The likelihood of erection problems increases with age. The US Massachusetts Male Aging Study (Journal of Urology 1994;151:54–61) reported erection problems in:

  • 25% of 65-year-olds
  • 55% of 75-year-olds
  • 65% of 80-year-olds.

This is because the older you are, the more likely that you have one of the medical conditions that damage blood vessels and nerves causing impotence.

Smoking. Smoking doubles your likelihood of erection problems. This is because if you are a smoker your arteries are likely to become clogged (atherosclerosis). During an erection the penis swells because it fills with blood. If your arteries are clogged, the blood cannot flow in efficiently and your erection will not be as good.

A study of 4,462 Vietnam war veterans, aged between 31 and 49, showed that smokers had a 50–80% increase in the risk of impotence compared with non-smokers. Another study has shown that for every year you smoke 20 a day, you increase your risk of impotence by 2–3%.

According to a British Medical Association report (ASH/BMA 1999) about 120,000 men in the UK in their 30s and 40s are impotent as a result of smoking.

Unhealthy lifestyle. A sluggish lifestyle, in which you spend a lot of time watching TV and are overweight, makes impotence more likely. A study (Journal of Urology 2006;176:217–221) concluded that there was a low incidence of erectile dysfunction in men who were healthy. However, obesity and smoking were associated with an increased risk of erectile dysfunction, while physical activity was associated with a decreased risk of erectile dysfunction. And according to another study (British Journal of Urology International 2012;110:540–545), the incidence of erectile dysfunction increased from 32% in men with a waist of 35inches to 75% in men with a waist of over 39 inches.

Distance cycling and motorcycling. If you decide to take more exercise, distance cycling may not be the best choice. About 1 in 5 distance cyclists notices some numbness of the genital area after a ride, and 13% experience problems with erections for the following week or longer. The cause is pressure of the saddle on nerves and arteries. For the same reasons, motorcycling may also increase the risk of erectile dysfunction. Choose a wide saddle with plenty of padding that makes you sit back firmly, and dismount if you start to experience numbness.

Psychological factors can, of course, cause impotence. These include:

  • guilt
  • depression
  • losing interest in your partner
  • a partner who finds intercourse painful
  • low self-esteem
  • fear of not performing well.

Often both physical and psychological factors are involved. A physical problem impairs erections, and you then become so preoccupied with the question ‘Can I maintain my erection this time?’ that sexual arousal becomes impossible. Anxiety actually has the physical effect of contracting the muscles of the erectile tissue, preventing blood entering the penis and allowing the blood to drain away.


First published on: embarrassingproblems.com
Reviewed and edited by: Matt Brewer
Last updated: May 2021

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