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Key Takeaways
- A micropenis is a smaller than average penis that measures less than 3.67 inches when stretched.
- It is a rare condition caused by problems with hormones and genetics during fetal development.
- It might need treatment if there are emotional, fertility, or urination issues.
Micropenis occurs in roughly 1.5 out of every 10,000 U.S. births, primarily due to genetic or hormonal factors during early development that lead to small penis size. While not inherently harmful, exploring treatment can address physical or psychological effects, fostering a better quality of life.
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A Note on Gender and Sex Terminology
Verywell Health acknowledges that sex and gender are related concepts, but they are not the same. To accurately reflect our sources, this article uses terms like “male,” “man,” and “boy” as the sources use them.
What Defines a Micropenis?
Micropenis is a relatively rare condition affecting 1.5 of every 10,000 boys born in the United States. It is defined as a stretched penile length (SPL) that is at least 2.5 standard deviations smaller than the average SPL for other males of that age.
(In statistical terms, a standard deviation of 2.5 translates to 99.4% of the studied population.)
In adults, a micropenis is considered a stretched, flaccid (soft) penis length of 3.67 inches or less. This contrasts with an average SPL of 4.72 to 5.87 inches in men.
In infants and boys, micropenis is broadly characterized as follows:
| Age | Length |
|---|---|
| 0 to 5 months | 0.75 inches (1.9 cm) or less |
| 6 to 12 months | 0.9 inches (2.3 cm) or less |
| 1 to 2 years | 1.02 inches (2.6 cm) or less |
| 2 to 3 years | 1.14 inches (2.9 cm) or less |
| 3 to 4 years | 1.3 inches (3.3 cm) or less |
| 4 to 5 years | 1.38 inches (3.5 cm) or less |
| 5 to 6 years | 1.5 inches (3.8 cm) or less |
| 6 to 7 years | 1.54 inches (3.9 cm) or less |
| 7 to 8 years | 1.46 inches (3.7 cm) or less |
| 8 to 9 years | 1.5 inches (3.8 cm) or less |
| 9 to 10 years | 1.5 inches (3.8 cm) or less |
| 10 to 11 years | 1.46 inches (3.7 cm) or less |
| Post-puberty | 3.67 inches (9.3 cm) or less |
What Causes Micropenis?
A micropenis is the result of abnormal fetal development that starts quite early in the pregnancy, generally between eight and 12 weeks of gestation.
During this time, the hormone human chorionic gonadotropin (hCG) stimulates testosterone production in the fetal testicles, aiding penis growth into the later trimesters. After birth, luteinizing hormone (LH) continues to stimulate testosterone production and penis growth, especially between the first and third months of life.
Any disruption in these processes can affect penis development, leading to micropenis. Genetics and congenital disorders are key factors. Micropenis often occurs with conditions such as:
- Kallman syndrome: A genetic disorder preventing the start or completion of puberty. It’s part of the hypogonadotropic hypogonadism conditions.
- Prader-Willi syndrome: Usually inherited from the father, it causes behavioral issues, intellectual disability, undescended testicles, micropenis, and short stature.
- Klinefelter syndrome: A genetic condition that randomly occurs, resulting in an extra X chromosome in males. This often leads to low testosterone and little or no sperm production.
- Noonan syndrome: Impacts normal development, causing short height, skeletal issues, undescended testicles, and delayed sexual development.
- Androgen insensitivity syndromes: Occur when the body’s receptors don’t respond to testosterone.
- Anorchia (absence of testes)
- 5 alpha-reductase deficiency: This is a genetic disorder that affects sexual development before birth and during puberty due to the lack of the active form of testosterone, known as dihydrotestosterone (DHT).
- Congenital growth hormone deficiency: Also known as pituitary dwarfism, this genetic condition is caused by insufficient amounts of growth hormone (GH), resulting in short stature with normal body proportions.
- Bilateral anorchia: This is a congenital defect of unknown origin characterized by the absence of both testicles, resulting in underdeveloped genitals due to the lack of testosterone.
Less common causes or contributing factors for micropenis include:
- Estrogen-based fertility drugs: There is evidence that fertility drugs like diethylstilbestrol (DES) may cause smaller-than-normal penis size if taken during early pregnancy.
- Environmental pollutants: Some research suggests that exposure to chlorinated pesticides during pregnancy may cause micropenis and other genital abnormalities in babies.
In many cases, the cause of micropenis will be unknown.
How Is It Diagnosed?
Micropenis is typically recognized and diagnosed at birth. To do so, a healthcare provider will measure the stretched penis length on the dorsal (top) side of the penis. This more closely corresponds to the erect penis length.
Less commonly, micropenis may only be recognized as a boy gets older and his penis is significantly smaller than the average for his age.
Because there is a lot of variation in penis size during puberty, a measurement alone cannot diagnose micropenis during this rapid growth phase. Instead, mathematical calculations will be used to establish if the SPL is less than 2.5 standard deviations for the boy’s age.
To help pinpoint the possible causes, other tests and procedures may be ordered, such as:
- Blood tests to check for abnormal values in testosterone, LH, GH, and hCG
- Pelvis ultrasound to evaluate the testicles and other internal genital structures.
- Magnetic resonance imaging (MRI) of the brain to check for abnormalities of the pituitary gland which directs the production of testosterone and other hormones in the body
Possible Complications
Other than its smaller size, a micropenis doesn’t work differently than a normal penis and doesn’t necessarily affect self-esteem. In fact, research has shown that people with micropenises have similar masculine self-images as men of average or above-average penis size.
With that said, micropenis can cause complications in some men that may require medical or psychological treatment, including:
- Loss of fertility: A penis length of less than 2 inches is associated with a lower likelihood of conception. Some people with micropenis may have a low sperm count if an underlying pituitary disorder is involved.
- Urination problems: A micropenis can sometimes make it difficult to direct a urine stream while standing. While sitting on the toilet may help compensate for this, some men will experience skin irritation and urinary tract infections (UTIs) as a result of splashback or soiling.
- Psychological distress: In some men, micropenis can impact self-esteem, cause performance anxiety, affect relationships, and lead to social isolation and depression.
Are There Ways to Treat a Small Penis Size?
A micropenis requires no treatment if sexual function, fertility, urination, and moods are not unaffected. For those who are affected, different treatments may be considered, including:
- Testosterone therapy: Infants and children with micropenis with 25-milligram injections of testosterone given in 21-day intervals. The injections may increase penis size to the appropriate age range and are most effective in children under 3 years of age (although it may benefit boys up to age 8).
- LH-FSH therapy: This involves injections of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in addition to testosterone therapy during the first years of life. Doing so may nominally increase the stretched penis length compared to testosterone alone..
- Topical DHT: Dihydrotestosterone (DHT) is the more active form of testosterone. When formulated as a topical gel and applied to the penis, it has been shown to increase the stretched penis length in some, but not all, boys prior to and during puberty.
- Suspensory ligament release: This form of penile enlargement surgery involves the cutting of the ligament that supports the penis during an erection. Once released, the penis will drop forward at a different angle, making the penis look larger and possibly aiding with urination.
- Assisted fertility: In men who want to pursue fatherhood but have not been able to conceive, assisted fertility techniques like intra‐uterine insemination (IUI), in vitro fertilization (IVF), and intracytoplasmic sperm injection (ICSI) may be explored.
- Gender reassignment surgery: This is a controversial treatment that was once recommended for children with micropenis, but is rarely used today. This was more in response to a general cultural discomfort with small penis size rather than a real medical need.
- Psychotherapy: For men who experience unremitting psychological distress, treatments like cognitive behavioral therapy (CBT) can also help identify and change negative behaviors and better deal with issues related to self-esteem and performance anxiety.