What is a Micropenis?

Many men worry about the size of their penis; however, not many realize that there is an actual medical condition where the size of the penis is referred to as a "Micropenis."

But how small is a Micropenis? What causes the condition? And how is it treated?


Statue penis

How small is a Micropenis?

As the prefix 'micro' suggests, people with a Micropenis have a relatively small penis. But how small exactly is a Micropenis?

The condition refers to any penis that, when stretched, is 2.5 standard deviations below the mean size for the patient's age. (1)

What do 2.5 standard deviations below the mean work out as?

In adults, the condition refers to any penis smaller than 2.8 inches in length. (2)

In infants, a Micropenis is classed as any penis less than 0.75 inches in length. This is considered significantly smaller than a "normal" male newborn's penis, which is between 1.1 and 1.6 inches in length when stretched gently. (3)

What problems does having a Micropenis cause?

Having a micro-penis can cause several problems, including difficulty urinating and having sexual intercourse.

Fertility can also be affected. Some people with Micropenis have a low sperm count, which results in infertility or decreased fertility. (4)

The condition can also have a significant impact psychologically. Many men with the condition have very low self-esteem, and some even suffer from depression. (2)

What causes Micropenis?

Micropenis is caused by the male baby's penis failing to elongate after the first trimester of pregnancy. (5)

The cause of this is thought to be a hormonal problem. Specifically, it is believed to be due to insufficient testosterone levels, a male sex hormone.

The inadequate levels of testosterone may come as a result of insufficient production of testosterone during the second and third trimesters of pregnancy or as a result of the unborn child not responding to the produced testosterone. (6)

Research carried out on Japanese patients and published in the Journal of Clinical Endocrinology & Metabolism found that genetic mutations of the SRD5A2 gene can cause Micropenis. (8)

The SRD5A2 gene, or the steroid-5-alpha-reductase, alpha polypeptide 2, codes for the enzyme steroid 5-alpha reductase 2. This enzyme processes the hormone testosterone to dihydrotestosterone (DHT), a more potent androgen. (9)

Researchers have also found that a genetic condition may make boys more susceptible to the development of Micropenis triggered by factors in the environment.

Specifically, they found a polymorphism in the gene for the aryl hydrocarbon receptor repressor (AHRR), called the Pro185Ala polymorphism, which may cause susceptibility to the development of Micropenis in response to dioxins, a type of environmental endocrine disruptor. (7)

Moreover, there is even further research to suggest that newborn male external genital malformations, such as Micropenis, may, in part, be caused by environmental chemicals such as pesticides. (10)

Incidence of Micropenis

Despite not being commonly discussed, the condition is thought to affect 1 in 200 males that are born. (2)

Historical treatment of Micropenis

Historically, Micropenis was treated by gender reassignment of the baby at birth. (6)

This meant that parents were advised to bring their genetically male children up as females. (11)

John Money, the founder of the Gender Identity Clinic at John Hopkins University Medical Centre in Baltimore, advocated gender reassignment. (12, 13)

In 1975, he published a paper outlining the success of a gender reassignment study in which a twin son had been successfully brought up as a girl. (11, 12)

Money's study was, however, later discredited by Milton Diamond and later journalist Colapinto, who both showed that the gender reassignment had not been a success. (12)

Specifically, the genetically male child brought up as a female decided to change back to her original gender when she discovered the truth about her gender reassignment. Moreover, in 2004, the patient took his own life. (12)

Treatment of Micropenis

Nowadays, according to Mairi MacDonald, the UK Intersex Association (UKIA) views cosmetic surgery of the genitals to reassign an infant's gender from male to female, solely due to the child having a small penis, as "child abuse." (5)

Instead, they advocate hormone therapy called testosterone replacement. This can produce a penile length within the "normal range." (5)

Micropenis can also be treated with surgery called phalloplasty. (2)

Phalloplasty often involves using skin from the patient's forearm. This skin is wrapped around the native penis, and an inflatable penile prosthesis is inserted to provide an erection. (6, 14)

Researchers have found that this procedure produced a penis that could be used for sexual intercourse regularly and remained stable for the long term. (14)

The procedure is, however, high-risk and can lead to complications. (6)

Further Reading

Last Updated: Jul 22, 2023

Emily Henderson

Written by

Emily Henderson

During her time at AZoNetwork, Emily has interviewed over 300 leading experts in all areas of science and healthcare including the World Health Organization and the United Nations. She loves being at the forefront of exciting new research and sharing science stories with thought leaders all over the world.


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  1. John Nick John Nick Greece says:

    In 2011, researchers used Human Chorionic Gonadotropin (hCG) injections on patients with micropenis and achieved which resulted in a penile increase from a mean 5.41±1.43 cm to 7.45±1.70 cm so you might want to include that as well in your article.

  2. Jay Fazekas Jay Fazekas United States says:

    I suffer from this condition its so embarasing I got teased in school because of it I change in bathroom stalls when I go swimming have no sex life!

  3. Hervé Duo Hervé Duo France says:

    On this website it says that a micro penis is a penis under 7cm  for the same calcul : average penis -2,5*standard deviation.

  4. John Dugan John Dugan United States says:

    Many men who fear that they have a micropenis are really only a bit small. Such men need worry less about size and should instead put time into ensuring that their penis health is adequate. One way to do this is to regularly use a top notch penis health crème with vital amino acids.

  5. Clarissa Hope Clarissa Hope United States says:

    I'm 60, with a micropenis of 2.25 inches (5.7 cm) in stretched length and  2.7 inches (6.8 cm) circumference. I have been comfortably asexual and single unmarried my entire life with intense desire to feminize myself and to fully dress and behave as female. For over five years I have kept a medically prescribed regimen of Estradiol 6 mg/day, Micronized Progesterone 10 mg/day, Spironolactone 100 mg/day and Finasteride 5 mg/day with no problems noted. Since I have no desire to be penetrated, the only reason for me to have SRS "bottom surgery" would be purely personal cosmetic. Hardly a day goes by when I do not wish to have my testicles removed for being the useless hanging bikini-zone nuisance they truly and constantly are, yet I fear their removal would eliminate even the infrequent desires for self-gratification I amazingly still have. I consider myself blessed with a gift for incredibly persistent happiness, facial features way more pretty and feminine rather than handsome and masculine and a metabolism that makes it easy for me to stay slender and healthy - all of which help me to enjoy my passion for extremely indulgent crossdressing to the greatest extent. If I had my life to do over I would not change a thing and I attribute all the above, whether directly or indirectly, the result of being semi-feminized via hormonal exposure in-the-womb from either increased estrogen, decreased testosterone or both.

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
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