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Last updated November 11, 2019. 5 minute read

What is a micropenis? Causes and treatment

A micropenis (or microphallus) is a penis that is 2.5 standard deviations from normal penis size. A standard deviation (SD) is a measure of how spread out a bunch of numbers are from one another.

Self Written by Michael Martin
Reviewed by Jefferson Chen, MD

A lot of men worry that their penises are smaller than average. Statistically speaking, the vast majority of them are absolutely wrong: The average male penis size is 5.16 inches erect, and 90% of men are within one inch of that measurement. But in rare cases, some men have an abnormally small penis, known as a micropenis.


  • A micropenis is a penis that is 2.5 standard deviations smaller than the average penis size, or less than 3.66 inches flaccid and stretched.
  • Most cases of micropenis are diagnosed at birth or in infancy.
  • Micropenis can result from testosterone deficiency, hormone disorders, environmental exposure, or no clear reason at all.
  • A micropenis can be improved with hormone treatment before puberty.

What is a micropenis?

A micropenis (or microphallus) is a penis that is 2.5 standard deviations from normal penis size. A standard deviation (SD) is a measure of how spread out a bunch of numbers are from one another. According to this study, 68 percent of men will have a penis (flaccid-stretched) that’s 13.24 ± 1.89 cm, and 95 percent will have a penis that’s 13.24 ± 3.78 c.

What this all means is that any adult male penis that is less than 3.66 inches when flaccid and stretched (called stretched penile length) is technically a micropenis. 


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The condition is usually diagnosed during a physical examination at birth or in infancy. According to the Cleveland Clinic, the primary symptom of micropenis is a penis that measures less than 1.9 cm (0.75 inches) in stretched penile length in infancy. The average penile length for a newborn boy is 3.5 cm (1.4 inches).

A micropenis is very uncommon. Only about 0.6 percent of men worldwide have the condition, and 0.015 percent (1.5 in 10,000 births) of boys in the United States are born with micropenises.

Causes of micropenis

A micropenis can happen for a few different reasons.

Testosterone deficiencies during pregnancy. Micropenis is usually caused by testosterone deficiency in utero. That can happen if the fetus doesn’t produce enough testosterone. 

In hypogonadotropic hypogonadism, a problem with the hypothalamus (a region of the brain region)or the pituitary gland fails to secrete the hormones that tell the testes to make testosterone. This means that penile growth in utero (and, later, puberty) is never stimulated.

Another cause of micropenis is when the mother’s placenta can’t produce enough human chorionic gonadotropin (hCG), a hormone that stimulates the development of testosterone in the fetus (Kim, 2011).

Hormonal abnormalities. Sometimes the body may not produce enough androgens (male sex hormones) in utero, or can’t respond to androgen properly, a condition called androgen insensitivity syndrome. Or the testicles may not have formed properly, called testicular dysgenesis (Grant, 1975). Rarely, a child may be born with an extra X chromosome, which can cause a shortage of testosterone and lead to micropenis.

Exposure to pesticides or toxins during pregnancy. In rare cases, a mother’s exposure to certain chemicals during pregnancy has been associated with her fetus developing a micropenis (Garcia, 2017).

Idiopathic. In some cases, the causes of a micropenis may be unknown.

Conditions associated with micropenis

Some men with micropenis may have a low sperm count. That can lead to infertility or decreased fertility. 

A micropenis might also be a sign of a growth hormone deficiency (Levy, 1996). 

Abnormal genetics can also be responsible: This can result in hormone disorders known as androgen insensitivity syndrome (CAIS) or partial androgen insensitivity syndrome (PAIS).

A man with a micropenis might feel anxiety about sex, even though sexual function with a micropenis is normal. Having a micropenis doesn’t affect erection, orgasm, or urination. 

Conditions mistaken for micropenis

Some apparent cases of micropenis are actually what experts call “inconspicuous penis” — meaning that fat or skin in the pubic area is obscuring the penis. These conditions can be pretty easily corrected.

Buried penis
In people with overweight or obesity, the penis may be less visible because of fat pads surrounding the penis. In people of any weight, the penis might be “buried” under excess foreskin or an unusually large scrotum (Srinivasan, 2011). 

Webbed penis
In this condition, skin from the scrotum is connected to a normal-size penile shaft.

Trapped penis
This can happen when post-circumcision scarring “traps” the penis in fat around the pubis, or within the scrotum (Srinivasan, 2011). 

Treatment options

There are several treatment options for micropenis. Experts say the best results can be obtained if treatment is started before puberty. A primary care doctor may refer a young patient with a micropenis to a pediatric endocrinologist (a hormone expert) or pediatric urologist. Blood tests can help determine any causes of micropenis and appropriate treatment.

Hormone therapy
In pre-puberty males with a micropenis, a healthcare provider may prescribe hormone therapy in the form of testosterone treatment — injections or a gel applied to the skin (Tsang, 2010). In patients with androgen insensitivity syndrome, topical DHT (dihydrotestosterone) may be applied to the peri-scrotal area. In those with hypogonadotropic hypogonadism, injections of the hormones luteinizing hormone (LH) or follicle-stimulating hormone (FSH) may be given.

Doctors may perform a phalloplasty, taking flaps of skin from donor sites elsewhere on the body. Or they may embed an implant under the penile skin. This surgery comes with a risk of complications (Rashid, 2013).

Does size matter? Not so much

Penetration and penis length are far from the end-all, be-all of a great sex life. 

If you have a penis that’s smaller than normal and have vaginal sex, keep in mind that the majority of nerve endings that provide pleasurable sensations during intercourse are right near the opening. Only 25% of women consistently orgasm from intercourse (Psychology Today, 2009) and some surveys have found it’s less (Herbenick, 2018). Most women climax from direct stimulation of the clitoris via oral sex, manual stimulation, or toys. The G-Spot is only 2 to 3 inches within the front vaginal wall, and many women who experience G stimulation find fingering or toys more reliable than intercourse.

If you have anal sex with men, remember that the prostate, a prime pleasure center, sits only two inches inside the rectum. And if you have anal sex with women, you can indirectly stimulate her G-spot with the same depth of penetration.