Erectile dysfunction (ED) results from a disruption in blood flow, nerve signaling, hormones, or psychological state, and often from several of these at once. It affects roughly 30% of men aged 35 to 49, climbing to 45% of those 50 to 64 and 63% of men 65 and older. While age is the single biggest risk factor, ED is not an inevitable part of aging. Understanding what drives it helps explain why it’s so common and what can be done about it.
How an Erection Works
An erection is a hydraulic event. When sexual arousal triggers nerve signals, smooth muscle tissue inside the penis relaxes and blood rushes in, increasing arterial flow up to eight times above its resting state. As the erectile tissue swells, it compresses the veins that would normally drain blood away. This trapping effect, reinforced by the stretching of the tough outer sheath of the penis, is what creates and maintains rigidity.
That entire sequence depends on a chain of events firing correctly: the brain sends signals down the spinal cord, parasympathetic nerves release a chemical messenger called nitric oxide, smooth muscle relaxes, arteries widen, and veins get squeezed shut. A breakdown at any point in that chain can cause ED. Most causes of erectile dysfunction ultimately interfere with one or more of these steps.
Blood Vessel Damage
The most common physical cause of ED is vascular disease, particularly atherosclerosis, the same process of arterial narrowing behind heart attacks and strokes. Fatty plaques build up inside the penile arteries, restricting blood flow. But the damage goes deeper than simple narrowing. The inner lining of the blood vessels loses its ability to produce nitric oxide, the key signal that tells smooth muscle to relax. Without enough nitric oxide, the arteries can’t dilate properly and blood can’t fill the erectile tissue fast enough or fully enough.
Over time, reduced blood flow starves the erectile tissue of oxygen. This triggers a cascade of structural changes: smooth muscle cells die off and get replaced by stiff collagen fibers. The outer sheath of the penis also becomes less elastic. These changes weaken the vein-trapping mechanism, so even blood that does enter leaks back out before full rigidity is achieved. This is why ED caused by vascular disease tends to worsen gradually rather than appearing overnight.
Because the arteries supplying the penis are smaller than those feeding the heart, they clog earlier. ED often shows up two to three years before a cardiovascular event, which is why doctors increasingly view it as an early warning sign of heart disease.
Diabetes and High Blood Sugar
Diabetes deserves its own category because it attacks erectile function from multiple directions simultaneously. Chronically elevated blood sugar triggers a series of biochemical reactions that damage both blood vessels and nerves at the same time.
High glucose leads to the buildup of harmful compounds called advanced glycation end-products. These compounds reduce nitric oxide availability and ramp up oxidative stress inside the blood vessel walls. The enzyme responsible for producing nitric oxide becomes less active, so penile arteries lose their ability to dilate on demand. Meanwhile, the same high-sugar environment damages the nerve fibers that carry arousal signals to the penis, causing demyelination (the stripping of the insulating layer around nerves) and outright degeneration of nerve endings.
On top of that, diabetes changes the physical structure of the erectile tissue itself. Elastic fibers decrease while collagen deposits increase, making the tissue stiffer and less capable of expanding. The result is that men with diabetes develop ED at younger ages, with greater severity, and it responds less well to standard treatments.
Nerve and Spinal Cord Injuries
Erections require intact nerve pathways running from the brain through the spinal cord and out to the penis. The parasympathetic nerves that trigger an erection originate in the lower spinal cord and travel through the pelvic plexus before branching into the cavernous nerves that enter the penis directly. Damage anywhere along this route can impair or eliminate erections.
Common culprits include spinal cord injuries, pelvic surgery (especially prostate removal, which runs close to the cavernous nerves), and conditions like multiple sclerosis that degrade nerve insulation. Even cycling for long durations can compress the pudendal nerve, which carries both sensory and autonomic fibers to the penis, causing temporary numbness and erectile difficulty.
Hormonal Causes
Testosterone plays a supporting role in erectile function rather than a starring one. It helps maintain the health of erectile tissue, supports nitric oxide production, and sustains sexual desire. When total testosterone drops below roughly 300 ng/dL, the traditional threshold for diagnosing low testosterone, ED becomes the most commonly reported symptom. Some research suggests symptoms can appear at levels as high as 320 to 375 ng/dL.
Low testosterone alone rarely causes ED in younger men, but it amplifies other causes. A man with mild vascular disease may maintain adequate erections until his testosterone also declines. Conditions that suppress testosterone include obesity, sleep apnea, chronic opioid use, and pituitary gland disorders. Thyroid imbalances and elevated prolactin levels can also interfere with erections through hormonal disruption.
Stress, Anxiety, and Depression
Psychological factors can cause ED on their own or make physically caused ED much worse. The mechanism is surprisingly concrete. Erections depend on the parasympathetic nervous system (the “rest and digest” branch), while stress activates the sympathetic nervous system (the “fight or flight” branch). These two systems work in opposition. Sympathetic activation promotes the release of norepinephrine, which contracts smooth muscle and actively reverses an erection.
Cortisol, the body’s primary stress hormone, appears to play a direct role as well. In men without ED, cortisol levels in the blood drop during sexual arousal, clearing the way for a normal erectile response. In men with ED, that drop doesn’t happen. Cortisol stays elevated or even rises slightly during arousal, potentially blocking the physiological chain reaction that produces rigidity.
This creates a vicious cycle. A man experiences ED once, perhaps from fatigue or alcohol. The next time, he’s anxious about whether it will happen again. That anxiety activates the sympathetic nervous system and keeps cortisol elevated, making failure more likely. Repeated episodes cement a pattern of performance anxiety that can persist even after the original trigger is gone. Conditions like depression and chronic stress can keep the stress-hormone system permanently activated, contributing to ongoing ED.
Lifestyle Factors
Smoking, obesity, heavy drinking, and physical inactivity all increase ED risk through overlapping mechanisms.
- Obesity: Body mass index is one of the strongest independent predictors of severe ED. Each unit increase in BMI raises the odds of severe ED by about 21%. Excess fat tissue converts testosterone to estrogen, promotes chronic inflammation, and accelerates vascular damage.
- Smoking: Nicotine constricts blood vessels and accelerates atherosclerosis. Smokers are significantly more likely to experience severe ED than nonsmokers, and the risk correlates with how many years and how heavily a person has smoked.
- Alcohol: Moderate drinking has a minimal effect, but chronic heavy use damages nerves, suppresses testosterone production, and causes liver dysfunction that disrupts hormone metabolism.
- Sedentary lifestyle: Regular aerobic exercise improves endothelial function, the ability of blood vessel walls to produce nitric oxide and dilate properly. Inactivity lets that capacity erode.
The encouraging flip side is that these are modifiable. Weight loss, smoking cessation, and consistent exercise have all been shown to meaningfully improve erectile function, sometimes enough to resolve mild ED without medication.
Medications That Can Cause ED
A number of commonly prescribed drugs list ED as a side effect. Among blood pressure medications, thiazide diuretics are the most frequent offenders, followed by beta-blockers. Alpha-blockers are less likely to cause problems. Certain antidepressants, particularly SSRIs like fluoxetine and sertraline, frequently interfere with sexual function by altering serotonin and dopamine signaling. Other drug classes linked to ED include anti-androgens used for prostate conditions, some anti-seizure medications, and long-term opioid painkillers, which suppress testosterone production.
If you suspect a medication is contributing to ED, it’s worth raising the issue with whoever prescribed it. In many cases, switching to a different drug in the same class can reduce or eliminate the sexual side effect without sacrificing the therapeutic benefit.
Why Multiple Causes Often Overlap
In practice, ED rarely traces back to a single neat cause. A 55-year-old man with high blood pressure, mild diabetes, 20 extra pounds, and a stressful job has vascular, neurological, hormonal, psychological, and possibly medication-related factors all contributing at once. This is why treatment that targets only one cause sometimes falls short, and why a combination of lifestyle changes, medication adjustments, and addressing psychological factors tends to produce better results than any single intervention alone.
Clinicians often use a brief five-question screening tool called the IIEF-5 to gauge severity on a scale of 5 to 25. Scores of 22 to 25 indicate normal function, 17 to 21 mild ED, 12 to 16 mild-to-moderate, 8 to 11 moderate, and 5 to 7 severe. Knowing where you fall on that scale helps guide the type and intensity of treatment that makes sense as a starting point.