Micropenis refers to an abnormally small penis. Micropenis is rare and hormonal or genetic issues are most often the cause. Doctors will usually diagnose and treat the condition at birth.
In this article, we look at the definition of micropenis, the symptoms and causes, and the ways a smaller-than-average penis may or may not affect sexual and other functions.
What is micropenis?
Doctors diagnose micropenis when a person’s penis is 2.5 standard deviations below the average stretched length for their age and level of sexual development.
Research has estimated that the average penis size for an adult is 13.24 centimeters (cm) or 5.21 inches when stretched. For adults, doctors consider micropenis for a stretched penile length of less than 9.3 cm or 3.66 inches.
When a person has micropenis, their internal genitalia and testicles are usually normal.
Clinical sources define average and micropenis sizes for each age range, as follows:
Age Average stretched length Micropenis stretched length
Newborn at 30 weeks 2.5 cm 1.5 cm
Newborn at 34 weeks 3.0 cm 2.0 cm
Newborn at full term 3.2 cm 2.4–2.5 cm
0–5 months 3.9 cm 1.9 cm
6–12 months 4.3 cm 2.3 cm
1–2 years 4.7 cm 2.6 cm
2–3 years 5.1 cm 2.9 cm
3–4 years 5.5 cm 3.3 cm
4–5 years 5.7 cm 3.5 cm
5–6 years 6.0 cm 3.8 cm
6–7 years 6.1 cm 3.9 cm
7–8 years 6.2 cm 3.7 cm
8–9 years 6.3 cm 3.8 cm
9–10 years 6.3 cm 3.8 cm
10–11 years 6.4 cm 3.7 cm
Adult 13.3 cm 9.3 cm
How common is micropenis?
Micropenis is a rare condition that may affect around 1.5 in 10,000 male newborns, or 0.015 percent of male newborns in the United States, according to estimates taken between 1997 and 2000.
The prevalence statistics of micropenis vary between studies. Micropenis and other birth abnormalities can be related to environmental factors, such as parental exposure to pesticides during pregnancy. As a result, this condition may be more common in specific populations.
Hormonal issues are the most common cause of micropenis. Less commonly, micropenis and other birth abnormalities can occur when the mother experiences exposure to pesticides or other toxic chemicals during pregnancy.
Testosterone deficiencies, during pregnancy, are usually the cause of micropenis and may also cause other genital abnormalities.
A testosterone deficiency can arise when a male fetus does not produce enough testosterone, or when the mother does not produce enough human chorionic gonadotrophin (hCG) hormone during pregnancy. hCG stimulates testosterone development in the fetus.
When testosterone levels are normal, some medical conditions can stop a person’s body from responding to testosterone correctly. This response is called androgen insensitivity.
When any of these hormonal issues arise, the penis of a male fetus may not develop in the usual way.
A male baby will experience a surge of testosterone around 0–3 months after birth. This is a crucial period for penile growth. If this process is interrupted by hormonal problems, a baby may have a smaller penis.
In rare cases, micropenis is idiopathic, which means that a doctor cannot find a specific cause.
Because hormone issues typically cause micropenis, people with this condition may have other symptoms, too.
Some diagnoses that doctors may associate with micropenis include:
- hypogonadotropic hypogonadism
- Prader-Willi syndrome
- Kallmann syndrome
- growth hormone deficiencies
- abnormal chromosomes
- Laurence-Moon syndrome
Sometimes what appears to be a micropenis is actually due to another problem. For instance, a baby born with swelling in the scrotum may look like they have a micropenis. The penis may also be less visible because of large surrounding fat pads when it is called buried penis and can occur in people with obesity.
How does someone know if they have micropenis?
Many people worry about penis size and typically think they are smaller than average even when they are not.
If a person suspects they have micropenis, they may wish to see a doctor, who will be able to take accurate measurements and diagnose the condition. A doctor will usually diagnose micropenis at birth, however.
If doctors suspect micropenis, they will measure the stretched length of the baby’s penis and check for other signs of hormonal abnormalities.
If a newborn’s penis is abnormally small, a doctor may perform tests to assess the cause, including:
- Physical exams: Alongside measuring the penis, a doctor may look for other signs, such as unusual fat pads or growths.
- Blood tests: These can help the doctor check the baby’s hormone levels. Doctors may also conduct genetic tests to determine the baby’s biological sex. In rare cases, a baby who seems to have a micropenis may be intersex or have a sex chromosome abnormality.
- Imaging scans: A doctor may use imaging tests, such as a pelvic ultrasound or an MRI scan, to see the genitals and surrounding structures.
Several other conditions can make the penis appear smaller than usual and may be confused with micropenis. Some of these can happen after circumcision.
Alternative diagnoses to micropenis include:
- buried penis, where a fatty pad hides the true size of the penis
- webbed penis, where there is extra skin connecting the scrotum and the penis
- trapped penis, where there is not enough skin surrounding the penis
Treatments aim to increase the penis size to ensure a person has a fully functioning penis and that they feel confident.
A doctor may recommend the following treatments for micropenis:
Testosterone treatments can often help the penis to grow. Applying testosterone cream to the genitals during infancy, or giving intramuscular testosterone injections can increase penis size.
Testosterone treatments are more effective before puberty than later on.
Doctors may consider that a good response to testosterone treatment is a 100 percent increase in the penis length or an adequate response as a 3.5 cm increase in length.
Different hormone treatments may help, depending on the cause of micropenis, so it is important that a person gets an accurate diagnosis.
If hormone treatments do not work, surgery may help. A doctor can put an implant into the penis, which may make it look larger than before. However, this surgery carries a high chance of complications.
Does micropenis affect sexual function?
Most people with micropenis have normal sexual functioning. Micropenis does not affect a person’s ability to urinate, masturbate, or orgasm. Some people may find it more difficult to urinate standing up.
Anxiety about penis size can be a barrier to enjoying sex with a partner. Men may remain unsatisfied with their appearance even with treatment, though research shows that many men have normal sexual identities and functioning. Even so, people may benefit from counseling or sex therapy.
Sexual intercourse is just one of many ways to enjoy sex with a partner. If a person has difficulties with sexual intercourse, this does not have to be a barrier to sexual pleasure for men and their partners.
According to research from 2018, just 18.4 percent of women can orgasm with vaginal penetration alone Focusing on other sexual techniques, such as oral sex, may help a person feel more confident about sexual interactions, which can be a positive for both sexual partners.
Micropenis is a condition where the penis is 2.5 standard deviations shorter than the average stretched penis length for a person’s age.
Testosterone deficiencies during pregnancy can cause micropenis. Less commonly, genetic abnormalities or environmental conditions can cause the condition.
Micropenis is usually diagnosed and treated in infancy. Testosterone treatments in childhood show good outcomes. A person with micropenis may not obtain an average-sized penis, but this does not usually affect sexual functioning and identity.
A wide range of penis sizes is normal. People with smaller-than-average penises can still have healthy, active sex lives. Counseling and sex therapy can help people to overcome anxieties about penis size or sex.
Medically reviewed by Karen Gill, M.D.
Written by Zawn Villines