In most cases, seeing veins beneath the skin of the penis is perfectly normal and does not require medical attention.

Several factors influence vein visibility, including:

genetics
age
frequency and intensity of physical activity
cardiovascular health
underlying medical conditions

In this article, we discuss why the veins in the penis might appear prominent and what this means.

We also review potential underlying medical conditions that contribute to penis vein visibility and when to see a doctor.
Why does it happen?
The appereance of veins in the penis may vary with age.

There are several veins and arteries that carry blood to and from the spongy erectile tissue in the penis.

Veins may look larger than usual during and immediately following an erection. Although the appearance of prominent veins may cause alarm, they indicate healthy blood flow.

Genetics and age can influence skin thickness, which may make veins appear more prominent or bigger than usual.

Also, blood clots and other conditions that affect the cardiovascular system can trap blood in the veins, which may affect how these blood vessels look.
Do prominent veins affect erection or ejaculation?

Typically, prominent veins do not affect erectile function.

Conditions that affect blood flow, such as blood clots and atherosclerosis, can have a minor impact on erectile function.

Research suggests a close relationship between cardiovascular health and erectile function.

In a 2015 study, for example, researchers conclude that erectile dysfunction could be an early sign of cardiovascular disease.

Also, in an earlier study by the Heart Institute, the authors state that erectile dysfunction may precede heart attacks by 3–5 years.
Possible causes

Vein size and visibility may vary over a person’s lifetime. They can also change as a result of sexual activity, or due to an underlying health condition.

Some possible causes of prominent veins in the penis include:
Erection
The veins in the penis may appear larger during an erection.