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What causes erectile dysfunction?

Written by David Shusterman, MD, board-certified urologist, adapted from his book ED Unlocked. General information, not medical advice for your situation. Who publishes this site.

Erectile dysfunction (ED) is caused by a problem somewhere along the chain that produces an erection: the brain's signal, the nerves that carry it, the arteries that bring blood in, or the seal that keeps it there. The most common physical causes are narrowed or damaged blood vessels (often from diabetes, high cholesterol, high blood pressure, smoking or excess weight), nerve damage, low testosterone and certain medicines. Stress and anxiety are common causes too, and many men have a mix.

The good news is that each cause can be identified, and most are treatable. Knowing which one you have is what points to the right treatment. Here is how the pieces fit together.

How an erection works, in one minute

Inside the penis are two spongy cylinders. When you are aroused, nerves release a molecule called nitric oxide. It relaxes the smooth muscle in those cylinders, the arteries open, and blood rushes in.

As the cylinders swell, they press against a tough outer sheath and squeeze shut the small veins that normally drain blood out. Blood flows in but cannot easily leave, so pressure builds until the penis is firm. Doctors sum it up as signal, surge and seal.

A failure at any of those three steps causes ED. That is why one man's ED can look nothing like another's, and why the right treatment depends on the cause.

Blood vessel problems: the most important cause

The arteries that feed the penis are only 1 to 2 millimeters wide, smaller than the arteries of the heart. When cholesterol plaque and diabetes start narrowing blood vessels throughout the body, these small pipes show it first. The erection never gets fully firm.

The main risk factors are the familiar ones:

• Diabetes and prediabetes, which damage the smallest blood vessels and the nerves.
• High cholesterol and high blood pressure.
• Smoking, which narrows blood vessels and damages the erectile tissue. A meta-analysis of more than 28,000 people confirmed it as a major, independent risk factor.
• Excess weight, especially belly fat, which fuels inflammation, insulin resistance and lower testosterone.
• Inactivity, since erections depend on the same vascular fitness as climbing stairs.

Because the same disease affects the heart, ED of this kind can be an early warning sign. Read ED as an early warning sign for heart disease.

A seal that leaks, and nerves that do not signal

Some men get firm at first but lose the erection quickly, especially when arousal dips, such as when changing positions. This can be a venous leak: the cylinders do not expand enough to fully close the drainage veins, so the blood escapes. It is a real, mechanical diagnosis, not a personal failing.

Nerve damage is another cause. Diabetes can dull both sensation and the nerve messages that start an erection. Pelvic surgery, including prostate surgery, can injure the nerves as well.

The pelvic floor muscles also help trap blood in the penis. A pelvic floor that is either weak or chronically tight can contribute. Roughly a third of men with chronic pelvic pain syndrome also have ED.

Hormones, medicines and sleep

Low testosterone can lower desire, energy and erection quality. It must be confirmed with properly timed morning blood tests. See low testosterone and ED.

Medicines can play a role. Antidepressants called SSRIs, for example, commonly blunt desire and sensation. Never stop or skip a prescribed medicine on your own; talk to the prescriber about options.

Sleep apnea is an often-missed cause. Repeated drops in oxygen at night can disrupt testosterone, blood vessel function and nighttime erections. Loud snoring, pauses in breathing and daytime sleepiness are worth mentioning to your doctor.

Alcohol and drugs matter too. Heavy drinking impairs erections and, over time, damages nerves and hormones.

Stress, anxiety and the mind

An erection is something the body only allows when it feels safe and relaxed. When you are anxious, including anxious about whether you will stay hard, your body releases adrenaline. Adrenaline is a powerful blood vessel constrictor, and it can shut the erection down in seconds.

The clue is variability. If the problem disappears with a different partner, on vacation or first thing in the morning, but returns under pressure, the cause is often the mind rather than the plumbing. In a young, healthy man with normal tests, this is the usual story. Stress, depression and relationship strain are real causes and deserve real treatment.

Age is a factor, but not the whole story

In the Massachusetts Male Aging Study, about 40 percent of men in their forties reported some degree of ED, rising roughly 10 percent with each decade. But that figure counts even mild, occasional trouble. Complete ED was around 5 percent at age 40.

Much of the rise with age is driven not by birthdays but by heart disease, diabetes and obesity that build up over time. That means a great deal of it tracks health you can actually influence.

Test, do not guess

Because the causes overlap, the best approach is a proper evaluation: a medical, sexual and psychosocial history, a physical exam and basic blood tests, including cholesterol, HbA1c, thyroid and a morning testosterone. The results point to which link in the chain is failing.

When the cause is clear, you can choose the right treatment. See erectile dysfunction treatment options. New or persistent ED is a good reason to talk to a urologist. This article is general information, not medical advice for your situation.

Frequently asked questions

What is the most common cause of erectile dysfunction?

In men past middle age, the most common physical cause is reduced blood flow from narrowed or damaged blood vessels, often linked to diabetes, cholesterol, blood pressure, smoking or weight. Many men have more than one cause.

Can stress alone cause erectile dysfunction?

Yes. Anxiety releases adrenaline, which tightens blood vessels and can stop an erection. If erections are fine at some times and not others, stress is often part of the picture.

Can young men get erectile dysfunction?

Yes. In young men it is often related to anxiety or stress, but persistent ED can also come from medicines, hormone problems or early vascular risk, so it still deserves an evaluation.

Can medications cause ED?

Some can, including certain antidepressants. Do not stop a prescribed medicine on your own; ask your prescriber about alternatives.

Does ED always get worse with age?

Not necessarily. Much of the age-related increase comes from heart disease, diabetes and obesity, which you can often influence with treatment and lifestyle changes.