Micropenis Overview

Causes and Treatment of an Abnormally Small Penis

Table of Contents
View All
Table of Contents

Micropenis is an extremely rare condition that occurs in only 1.5 per 10,000 male children in the United States. The term is used when the penis is abnormally small compared to other normal-sized genital structures, including the scrotum, testicles, and perineum.

Micropenis is the result of abnormal fetal development. Experts believe it is triggered by a genetic aberration or hormonal abnormalities.

This article discusses the symptoms, causes, and diagnosis of a micropenis. It also covers the treatments available and ways to cope.

Micropenis Treatment Options

Laura Porter / Verywell

Micropenis Symptoms

At birth, a penis that is less than 0.75 inches in length is considered a micropenis. As an adult, a flaccid penis less than 2.75 inches in length is considered a micropenis. An erect penis is considered a micropenis if it is less than 5 inches in length.

Causes

A micropenis develops during gestation or before the baby is born. It will often be the only abnormality noted in the pregnancy.

One of the possible causes of this is the low production of human chorionic gonadotropin (hCG) during the early part of the pregnancy. This is a hormone that stimulates the developing testes to produce testosterone.

After 14 weeks, the growth of the penis falls under the influence of another hormone, known as luteinizing hormone (LH). LH also stimulates testosterone in the so-called Leydig cells of the testicles. If the production of LH or testosterone is blocked, the child's penis length may be affected.

Genetics may also play a role. While there is no single gene that causes a micropenis, the condition is commonly linked to such chromosomal disorders as:

  • Androgen insensitivity syndrome (AIS): A condition that causes the body to be resistant to androgens, which are hormones that occur at higher levels in males
  • Klinefelter syndrome: A condition caused by an extra X chromosome in males
  • Turner syndrome: A condition caused by a missing X chromosome in females
  • Down syndrome: A condition with a third copy of chromosome 21

There is also evidence that estrogen-based fertility drugs like diethylstilbestrol (DES) may cause smaller-than-normal penis size if taken during early pregnancy.

While environmental pollutants are a less common cause, some research suggests that exposure to chlorinated pesticides during pregnancy may cause micropenis and other genital abnormalities in male babies.

Diagnosis

In newborns, a healthcare provider must take a proper measurement of the baby's penis when diagnosing micropenis. They will measure the stretched penis length (SPL) rather than flaccid or loose. This more closely correlates to the erect penis length in boys and men.

For this, the healthcare provider needs to hold a rigid ruler firmly against the pubic bone at a right angle. The penis is then held at the sides with a tool just below the glans (head). It's stretched to its maximum length without pain. Newer syringe-like tools can be placed over the penis and suction the organ to its fully stretched length.

Correctly identifying a micropenis in babies is crucial as it offers the opportunity for a potentially effective treatment. The healthcare provider should also explore conditions commonly associated with a micropenis. These include problems with the pituitary gland, which produces hormones, or the hypothalamus, which controls the pituitary gland.

Defining Micropenis

For full-term newborns, a micropenis is defined as an SPL of less than 1.9 centimeters. For older boys and men, it's characterized by a penis length that's 2.5 standard deviations (SD) smaller than the average for the age.

As a guideline, the Harriet Lane Handbook from John Hopkins University defines micropenis as follows:

Age Length
6 to 12 months Less than 2.3 centimeters (0.9 inches)
1 to 2 years Less than 2.6 centimeters (1.02 inches)
2 to 3 years Less than 2.9 centimeters (1.14 inches)
3 to 4 years Less than 3.3 centimeters (1.3 inches)
4 to 5 years Less than 3.5 centimeters (1.38 inches)
5 to 6 years Less than 3.8 centimeters (1.5 inches)
6 to 7 years Less than 3.9 centimeters (1.54 inches)
7 to 8 years Less than 3.7 centimeters (1.46 inches)
8 to 9 years Less than 3.8 centimeters (1.5 inches)
9 to 10 years Less than 3.8 centimeters (1.5 inches)
10 to 11 years Less than 3.7 centimeters (1.46 inches)
Adult Less than 9.3 centimeters (3.66 inches)

The variations in average penis size from age 7 are due to the differences in development as boys approach puberty. By puberty, it becomes far more difficult to define micropenis by centimeters alone. Mathematical calculations are needed until puberty is complete.

Differential Diagnosis

While the clinical definition of a micropenis seems to offer a definitive roadmap for diagnosis, that's not always the case. This is especially true in boys over the age of 8.

Most prepubescent boys brought in by their parents because of an underdeveloped penis rarely have a micropenis. In most cases, the boy is either experiencing delayed puberty or obesity (obscuring the penis length with excessive pubic fat). Or he simply has a larger frame compared to an otherwise normal penis.

In cases like these, the term "inconspicuous penis" may be more appropriately applied. It may be secondary to congenital conditions such as penoscrotal webbing. This is a condition where the scrotum extends up the underside of the penis, creating an indistinct junction between the two.

Another possible diagnosis is a megaprepuce in which the foreskin cannot retract and balloons abnormally.

Treatment

The treatment of micropenis will vary between children and adults. Given that the genitals of babies and toddlers are still developing, testosterone treatment can support penis growth, often significantly. Surgical options, while limited, may be explored in boys and men whose penises have reached their maximum growth.

Depending on the treatment plan, the medical team may include a pediatrician, urologist, endocrinologist, geneticist, or psychologist.

Testosterone Therapy

A micropenis can be treated in infants and children with three monthly intramuscular (IM) injections of testosterone. Research shows one or two courses of three testosterone shots (25 to 50 milligrams) can increase penis size to the appropriate age range. The shots should be given in four-week intervals.

For a male baby with a micropenis, circumcision should be delayed until the testosterone therapy is completed. Generally speaking, the therapy is most effective in children under 3 but may benefit boys up to the age of 8.

Gender Reassignment

In the past, young children with a micropenis often underwent gender reassignment surgery. This was more in response to a general cultural discomfort with small penis size rather than a real medical need.

Today, that practice has largely subsided, with most experts questioning its wisdom. They cite the benefits of testosterone therapy, the need for lifelong male-to-female hormone therapy in later life, and the lack of individual consent.

If pursued, gender reassignment would generally be considered at a later age. That way, the child has the ability to make an informed choice and has undergone extensive psychological evaluation.

Penis Enlargement Surgery

Some men with a micropenis will opt to undergo penis enlargement surgery (phalloplasty) with varying degrees of success. One such operation, called a suspensory ligament release, involves the detachment of the ligament that supports the penis during an erection.

Doing so allows the penis to lie at an obtuse rather than an acute angle, creating the perception of greater length. Potential risks include nerve damage, loss of penile sensation, and erectile dysfunction. It could also lead to the retraction of the penis if scar tissue develops at the incision site. 

Other forms of phalloplasty, such as flap surgery (grafting skin from another of the body), are less commonly pursued. That's because they carry a considerable risk of complications and may interfere with sexual function.

Other techniques are more likely to increase the girth rather than the length of the penis. These include silicone implants (prostheses), synthetic dermal fillers, and subcutaneous fat injections. Even if length gains are achieved, it would only affect the flaccid length. The erect length would remain the same.

There are also commercially marketed penis pumps and stretchers that have not demonstrated consistent results in delivering gains in penis length. If achieved, they tend to be modest at best. These devices are intended for males with erectile dysfunction—an entirely separate concern.

Coping

From a practical standpoint, a micropenis may complicate urination by making it difficult to direct the stream. Many men will simply compensate for this by sitting on the toilet when urinating.

Reproduction

On a more significant note, a penis length of fewer than 2 inches is associated with a lower likelihood of conception. Moreover, some men with a micropenis will have a low sperm count as the result of an underlying pituitary disorder.

In such cases, assisted reproductive techniques are available to significantly improve one's chances of conceiving.

Emotional

While there are treatments that may enhance penis size, the reality is that some individuals will have a smaller-than-normal penis. Some people assume that this will cause inherent psychological harm. However, those beliefs are more reflective of our cultural attitudes about penis size rather than the person's individual experience.

Long-term research shows that men with micropenises have similar masculine self-images as men of average or above-average penis size.

Sexual

A micropenis doesn't interfere with a man's libido, sexual function, sexual satisfaction, erection ability, or capability for mutually gratifying sexual relationships.

Summary

Micropenis is a rare condition that's the result of abnormal fetal development. It can be due to genetic conditions or low hormone production. Healthcare providers will measure a newborn baby's penis to help diagnose the condition.

Early detection is important for effective treatment, which may include testosterone therapy.

11 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Hatipoğlu N, Kurtoğlu S. Micropenis: etiology, diagnosis and treatment approaches. J Clin Res Pediatr Endocrinol. 2013;5(4):217-23. doi:10.4274/Jcrpe.1135

  2. Walia R, Singla M, Vaiphei K, Kumar S, Bhansali A. Disorders of sex development: a study of 194 cases. Endocr Connect. 2018;7(2):364-371. doi:10.1530/EC-18-0022

  3. Mahawong P, Sinclair A, Li Y, et al. Prenatal diethylstilbestrol induces malformation of the external genitalia of male and female mice and persistent second-generation developmental abnormalities of the external genitalia in two mouse strains. Differentiation. 2014;88(2-3):51-69. doi:10.1016/j.diff.2014.09.005

  4. Street ME, Angelini S, Bernasconi S, et al. Current Knowledge on Endocrine Disrupting Chemicals (EDCs) from Animal Biology to Humans, from Pregnancy to Adulthood: Highlights from a National Italian Meeting. Int J Mol Sci. 2018;19(6):1647. doi:10.3390/ijms19061647

  5. Johns Hopkins Hospital, Kleinman K, McDaniel L, Molloy M. The Harriet Lane Handbook: The Johns Hopkins Hospital (Mobile Medicine). 22nd ed. Elsevier; 2020.

  6. Srinivasan AK, Palmer LS, Palmer JS. Inconspicuous penis. ScientificWorldJournal. 2011;11:2559-64. doi:10.1100/2011/238519

  7. Jones HW, Park IJ, Rock JA. Technique of surgical sex reassignment for micropenis and allied conditions. Am J Obstet Gynecol. 1978;132(8):870-7.

  8. Campbell J, Gillis J. A review of penile elongation surgery. Transl Androl Urol. 2017;6(1):69-78. doi:10.21037/tau.2016.11.19

  9. Tuğ E, Güntekin ergün S, Ergün MA, Dilek FN, Perçin EF. The relation between isolated micropenis in childhood with CAG and GGN repeat polymorphisms in the androgen receptor gene. Turk J Med Sci. 2018;48(2):430-434. doi:10.3906/sag-1710-183

  10. Tsang, S. When size matters: A clinical review of pathological micropenis. J Ped Health Care. 2010;24(4):231-40. doi:10.1016/j.pedhc.2009.05.001

  11. Lee PA, Houk CP. Outcome studies among men with micropenis. J Pediatr Endocrinol Metab. 2004;17(8):1043-53.

Additional Reading

By Jerry Kennard
 Jerry Kennard, PhD, is a psychologist and associate fellow of the British Psychological Society.