How Erections Work

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Erections happen in response to sexual arousal. Learn more about how and why.

By Kelly Burch  Medically reviewed by Matthew Wosnitzer, MD

For many people, erections are a part of day-to-day life. Erections happen when the penis gets hard and usually stands outward or upward. This happens most often in response to sexual arousal, but sometimes it can happen for no reason at all, particularly during puberty and during the teen years. Erections can go away after ejaculation or on their own. 

Although many people experience erections, there’s a lot most people don’t understand. The ability to get and maintain an erection can cause stress for some people.

Here’s what you should know about how erections work, including how hard an erection should be, erectile problems, and tips for better erections. 

Anatomy of an Erection

An erection occurs when blood flows into the penis faster than it flows out. This causes the tissue in the penis to swell up and become hard. To understand how this happens, it’s helpful to know a bit more about the anatomy of the penis

The shaft of the penis has two different types of tissue that change when you get an erection:

  • The corpus cavernosa: Also known as erectile tissue. This tissue runs in two columns, along the sides of the penis. The corpus cavernosa is made up of muscle, collagen, and fiber that surround empty areas. When a person is sexually aroused, blood rushes into these empty areas, filling them up and causing the penis to stand erect. Blood vessels at the base of the penis constrict, keeping the blood in the corpus cavernosa. If there is venous leakage (which can occur after pelvic surgery) this process can be difficult and there can be venous leakage.
  • The corpus spongiosum: A similar line of tissue that runs on the underside of the penis and surrounds the urine channel called the urethra. This area doesn’t become as enlarged as the corpus cavernosa, and it maintains a continuous blood flow in and out while a person has an erection.1

The tunica albuginea is a band of fiber near the base of the penis that constricts during an erection, compressing the veins that would normally allow blood to flow out of the penis. As sexual arousal passes, the tunica albuginea relaxes, allowing blood to flow out of the penis. As this happens, the penis becomes flaccid again.

Stages of an Erection 

Many people with penises are familiar with the ways that an erection progresses. Most people start with a flaccid—or soft—penis, which gradually grows swollen before becoming fully erect. 

Scientifically, there are five stages to an erection. They are:

  • Latent: During this phase, impulses from the brain signal sexual arousal, and the penis relaxes, allowing the corpus cavernosa to begin filling with blood. 
  • Tumescence: At this point, the penis is slightly swollen. The penile arteries become enlarged, allowing more blood flow into the penis. 
  • Erection: The tunica albuginea restricts blood from exiting the penis, increasing blood pressure in the penis and making the penis stand erect. 
  • Rigidity: As the penis continues to become more engorged, the veins that allow blood to exit the penis become more restricted, causing maximum hardness in the erection. During sexual activity, this stage occurs just before climax. 
  • Detumescence: After climax—or when the arousal has passed—the tunica albuginea relaxes, allowing blood to flow out of the penis. The penis returns to its normal, flaccid state. 

After having an erection and climaxing, many people have a refractory period, during which they can’t get another erection even if they’re stimulated. This can be as short as 15 minutes, or as long as a day or more.

How Hard Is a Normal Erection? 

An erection that is hard enough to allow for penetrative sex is considered a normal, healthy erection.3 This usually occurs at the erection and rigidity stages listed above. 

Scientists have a more precise answer: in most men, the pressure in the penis during an erection reaches 100 mmHg, a measurement of pressure.1 However, when it comes to evaluating your own erection, don’t worry about the numbers: if your penis is hard enough to penetrate a partner and reach orgasm, your erection is considered normal and healthy…


F. Kaskais Web Guru

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