An erection is when a penis hardens and enlarges due to filling up with blood. Erections typically occur when a person with a penis is sexually aroused, but it can happen spontaneously.

What is an erection?

An erection is when your penis becomes hard and enlarged from an increase in blood flow. This increase in blood flow makes your penis stand up and away from your body (erect). Sexual stimulation or excitement is the typical cause of an erection. But people can get random or spontaneous erections. Erections go away after you ejaculate, but can also go away without ejaculating.

Anatomy of a penis

To better understand how an erection happens, it helps to know what your penis is made of. A penis consists of:

  • Two chambers called the corpora cavernosa, which run the length of your penis and contain a maze of blood vessels shaped like a sponge. It has sponge-like spaces, which means blood can fill the open space.
  • The urethra, or tube that carries pee and semen (the fluid containing sperm), which runs along the underside of the corpora cavernosa.
  • Erectile tissue, two main arteries and several veins and nerves.
  • The shaft, the longest part of your penis.
  • The head (glans), which is at the end of the shaft.
  • The meatus, or opening at the tip of the head where pee and semen come out.


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How does an erection happen?

An erection begins with sensory and mental stimulation in your brain. Your brain sends messages to your penis via your nerves.

Essentially, these messages tell the muscles of your corpora cavernosa (this contains the sponge-like material) to relax, allowing blood to flow in and fill the open spaces. When the blood vessels of the corpora cavernosa relax and open up, blood rushes in to fill them. The blood then gets trapped under high pressure by a series of valves, creating an erection.

The tunica albuginea (a membrane surrounding the corpora cavernosa), helps to trap the blood in the corpora cavernosa, so you stay hard.

An erection is reversed when muscles in your penis contract, stopping the flow of blood. The pressure decreases and the valves open, letting the blood flow out. Your penis loses its erection and becomes flaccid (soft).

What is the average size of an erect penis?

The average length of an erect penis is about 5.1 inches (around 13 centimeters). How big your penis is when erect has nothing to do with the size of your penis when it’s soft. Some people with a smaller-than-average penis can have a longer-than-average erection and vice versa.


What are the three types of erections?

People most often associate erections with sex. But erections can happen without any sexual activity or when you’re asleep. Here are the three types of erections:

  • Reflexogenic erections happen when something touches your genitals and triggers arousal. This is probably the type you think of most often, like erections during masturbation or sexual foreplay.
  • Psychogenic erections happen when you think of sexual memories or fantasies. This type of erection happens without physical touch.
  • Nocturnal erections happen when you’re asleep. They occur more commonly during the deep stages of sleep.

Why a person can’t get an erection

Erectile dysfunction (ED) happens when a person can’t get or keep an erection that’s hard enough for sexual intercourse. It’s a common condition that affects at least 10% of people.

A number of factors can cause ED, including:

  • Vascular disease: Blood supply to your penis can become blocked or narrowed as a result of vascular diseases like atherosclerosis due to high blood pressure, high cholesterol, diabetes or tobacco use.
  • Neurological disorders: Nerves that send impulses to your penis can become damaged from stroke, diabetes or other causes.
  • Psychological state: These include stress, depression and performance anxiety.
  • Trauma: An injury could contribute to symptoms of ED.
  • Certain medications: Several different types of medication can affect erections.
  • Surgery on your prostate, bladder or another organ in your reproductive system.

Medications to help with an erection

Your healthcare provider may prescribe medication to help with ED. Some examples of oral medications include sildenafil (Viagra®), vardenafil (Levitra®) or tadalafil (Cialis®). If low testosterone is the cause of erectile problems, your provider may recommend testosterone therapy.

If medication doesn’t help, there are nonsurgical treatments like using a vacuum erection device (penis or penile pump) or getting penile injections. A suppository you put inside your penis can also be an option.

Be sure to discuss all treatment options with your healthcare provider so you can decide what method works best for you.

Several other nonsurgical treatments are currently being studied including focused low-intensity shockwave therapy. Another treatment called radial wave therapy has been shown to be ineffective for treating ED. At this time, these treatments aren’t FDA-approved for ED, and further research is needed.


How long can the average man stay hard?

An erection can last anywhere from a few minutes to a few hours. There isn’t really an average time for how long an erection should last. In general, though, the average amount of time a person has an erection during sexual intercourse before they ejaculate is about seven minutes.

Several factors can affect how long an erection lasts. Age, medications, stress or being under the influence of alcoholic beverages are examples of factors that influence an erection.

Go to the emergency room if you have an erection that lasts longer than four hours. An erection lasting longer than four hours is a condition known as priapism.

What makes someone maintain an erection?

How you get and maintain an erection is extremely personal and unique to your body. It’s worth noting that erectile problems may occur as you age, or as you develop other health issues. Your healthcare provider can discuss your situation with you and develop a treatment plan if you feel your erections aren’t hard enough or don’t last long enough for enjoyable sex.

Generally speaking, though, there are some things you can do that help your erections. Examples include:

  • Eat a healthy diet and maintain a body weight that’s right for you.
  • Take steps to prevent or manage high blood pressure, high cholesterol and other chronic conditions that may impact your ability to stay hard. Keep in mind, medications to treat these conditions can also sometimes affect your erections.
  • Exercise regularly. Most healthcare experts recommend at least 20 to 30 minutes of exercise per day.
  • Avoid misusing drugs and smoking cigarettes. If you drink alcohol, drink only occasionally.
  • Try to reduce or minimize your stress.

A note from Cleveland Clinic

There isn’t a one-size-fits-all solution to getting and maintaining an erection. The process starts in your brain and involves your nervous and circulatory systems. Being able to get and maintain an erection is important to your sexual and emotional health. ED can also be one of the first signs of a more serious issue like heart disease. Make an appointment with your healthcare provider if you’re concerned about your erections or are unable to get or maintain an erection. Treatment options are available to help you.

Medically Reviewed

Last reviewed on 04/06/2023.

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