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How does an erection function?

Category:Intimate health, Potency

The ability to get an erection is something that many people take for granted, but in order for it to happen, a lot of things actually need to be right. Certified sexual educator Åsa Enervik explains what is going on when you get hard.

To put it simply, an erection happens when the penis fills with blood and gets hard. But actually, the ability to get an erection involves a very complicated system whereby many parts have to work together.

Many things have to happen for you to get an erection

“To be able to get an erection, several things need to click, both in your head and body. You need to feel relaxed, have desire and we need to function purely anatomically and physiologically for the system to work as it should”, says Åsa Enervik, certified sexual educator.

There are three swelling parts in the penis, two in the shaft and one in the glans. It is the ones in the shaft that fill with blood and get hard when you have an erection. You can get an erection for a number of reasons, from sexual touch or thinking about something that turns you on, for example. You can also sometimes get a hard on from things that have nothing to do with sex – clothes that rub in a certain way, or when we sleep, for example.


The brain affects erections

“The process can start in slightly different ways, but what causes the penis to fill with blood is that the brain sends signals that cause the muscles around the blood vessels to relax. The blood vessels relax and dilate and then more blood flows into the penis. When the swelling parts fill and get bigger, less blood flows out of the penis and the process reinforces itself,” says Åsa Enervik.

That hard state continues until you ejaculate. After that, you end up in what is called the rest phase, when the blood vessels contract again and the valves relax, causing the blood to flow out.


Stress prevents blood vessels from relaxing and then the blood cannot flow out into the penis, no matter how much you want it to. Åsa Enervik, Barnmorska, RFSU

Stress is an erection killer

The fact that relaxation in the blood vessels is so important to being able to get an erection is also an explanation as to why stress is a real erection killer.

“Stress prevents the blood vessels from relaxing and then the blood cannot flow out into the penis, no matter how much you want it to. Such stress can, for example, come from the fact that you had difficulty getting an erection the last time you had sex, or that you feel performance anxiety. It becomes a vicious circle,” says Åsa Enervik.

The fact that having an erection is such a sensitive process means that we need to be aware of how it works both physically and psychologically in order to understand what lies behind erectile problems.


Last updated: 2023.10.04