Penis Size Defined

Dr. Greene's Answer

“It’s a boy!”

When we first glimpse our children in the delivery room, their sex is one of the immediate things we notice. It’s also one of the first things we report to family and friends. In the last generation, many of us have seen evidence of our children’s sex on ultrasound even before they were born, but still at the birth, we look to see.

How disconcerting to parents when a boy’s penis seems to disappear, either at birth or shortly thereafter. The good news is that the outlook is bright. Sometimes surgery is needed, sometimes medical treatments, and often nothing at all.

How is penis size defined? Any condition in which the penis is considered absent or especially small is categorized as “inconspicuous penis.” Within this umbrella term are several types of diagnoses, each with their particular traits and methods of treatment. These include webbed penis, concealed penis, trapped penis, micropenis, and absent penis. Such conditions are caused by a variety of factors, including, but not limited to, hormone levels, circumcision, and the consumption of harmful chemicals, called phthalates, present in some plastics. The variations of inconspicuous penis are outlined below, as well as information on phthalates and how to avoid them.

Webbed Penis

Webbed penis refers to an average sized penis where the skin of the scrotal sack extends part way up the shaft of the penis. Some children are born with this condition, and others may develop it due to an aggressive circumcision. In this case, adhesions form between the scrotal and penile skin as the circumcision attempts to heal. 

Webbed penis does not interfere with any of the various penile functions, and usually causes no issues unless multiple circumcisions are performed in an attempt to cut back the skin. A webbed penis is unlikely to change unless surgery is performed, but surgical outcomes are often highly successful

Concealed Penis

A concealed penis is an average sized penis that is hidden within the pad of fat that resides over the pubic bone. It is sometimes called buried or hidden penis. Concealed penis can occur from birth, or post-circumcision. It is relatively common in infants and toddlers, but can occasionally occur in older children or adolescents who are obese. 

If the penis can easily be exposed by gently pulling on it or by depressing the surrounding fat pad, then there is a good chance it will grow normally and reveal itself over time. Occasionally surgery is needed to correct concealed penis, but either way, the outlook is quite positive for children with this condition. 

Trapped Penis

Trapped penis refers to a penis of average size that is partially stuck in the pubic fat pad. Children with this condition are not born this way, but it develops as a result of circumcision. Circumstances that cause this include the routine circumcision of a webbed penis, or when circumcision coincides with significant scrotal swelling from a hydrocele or hernia. Scarring or adhesions then partially trap the penis within the pad of fat. This is an unfortunate case that can predispose children to urinary tract infections or urinary retention. In the case of trapped penis, surgery is usually advisable in order for it to function normally.

Penis Size Defined: Average Penis Size — Stretched Penile Length

All of the above conditions have a penis of normal size. In determining size, the “stretched penile length” is far more important than the “relaxed length.” To evaluate penis size, stretch the penis gently and measure from the bone at the base all the way to the tip. Be sure to depress the surrounding fat pad to get all the way to the base. Here are the normal values (Adapted from Feldman KW, Smith DW. Journal of Pediatrics. 1975; 86:395):

Some limited growth of the penis does occur between 0 and 5 years of age, and again a small amount between 5 years and onset of puberty. Adult sized penis and testicles are generally reached about 5 years after onset puberty, but the exact timing is varied. 

Micropenis

Also known as microphallus, micropenis refers to penis length more than 2.5 standard deviations below the average size for age. For a newborn, a stretched length that is less than ¾ inch (1.9 cm) is considered micropenis. 

Cases of micropenis are considered to have hormonal origins, although the specifics of that have yet to be revealed. It is believed that a sort of hormonal imbalance occurs sometime after 14 weeks gestation, once the penis has formed. Babies born with micropenis should have their hormone levels monitored, in addition to checking chromosomes in order to assess for any underlying genetic syndrome. It’s also helpful to get an MRI to check hormone-secreting glands. 

Often the first step in treatment may be a three-month trial of testosterone supplementation. If the penis grows in response to testosterone, the outlook is hopeful for average adult penis size and function. 

Even if there is no response to hormone treatment, some studies of micropenis have found that even if a boy grows up with a small penis, most are able to stand to urinate, maintain normal erectile function, and be sexually active. Their partners also report sexual satisfaction. In the past, doctors would recommend gender reassignment surgery for children with micropenis who did not respond to testosterone therapy. However, this opinion has changed given that many children with micropenis can maintain healthy functionality of the penis, and some adults who have received treatment for intersex conditions argue strongly against gender reassignment before the child is old enough to choose. Penile prosthesis are available to children if desired, or if peer teasing is an issue. For families considering reassignment surgery, there are a growing number of gender clinics across the country that can provide individualized counseling and treatment for families exploring this option.

Absent Penis

Also called penile agenesis, this condition is very rare, affecting only 1 in 20 million children. Typically in such cases the scrotum and testicles form normally, but there is no penis. If your child is born with this condition it’s important to consult not only your pediatrician but also a geneticist, endocrinologist, urologist and mental health expert. Their collective assessment can be helpful in deciding what measures to take for the health and well-being of your child. 

The Trouble with Phthalates

Phthalates are synthetic chemicals found in many plastics, used to make plastics more pliable and less brittle. When absorbed in the body, phthalates have the capacity to affect hormones, including the increase of estrogens in the form of xenoestrogens. It’s well understood that high levels of phthalates make male animals more feminine, with altered genitals, altered behavior, poor-quality sperm, and increased infertility. But the effect on human babies has not been well studied. However, one sobering study suggests that exposure to phthalates before birth may under-virilize boys, which can be seen with a shorter penis length, thinner penis width, smaller and less distinct scrotum, shorter distance between the anus and scrotum, and higher likelihood of undescended testicles. The study was conducted by researchers from several medical schools, in conjunction with the National Center for Environmental Health. 

A study was done that tested the urine of pregnant women for 9 common phthalates. The tallied amounts varied considerably from woman to woman. Next, a different set of researchers collected measurements of 134 boys’ genitals. Babies whose mothers were in the top quartile of 4 of the different phthalates in their urine ranged from 3 to more than 10 times more likely to have an anogenital index (AGI) shorter than expected when compared to babies whose moms were among the 25 percent with the lowest levels of these particular phthalates. No differences were detected with the other 5 types of phthalates.

Phthalates are a relatively recent addition to manufacturing, new to the environment within about the last 50 years. Phthalates are found in plastic wraps, bags, medical equipment and toys, as well as other plastic products. They are also frequently used in the recipes of many personal care products, including makeup, lotions, shampoos and soaps, as well as paints and pesticides. Many organic products will proudly state they are free of phthalates. As these chemicals are extremely common, it is wise to seek out products that clearly say they do not include these additives. 

Take note! The chemicals from plastics, paints, pesticides, and personal care products are absorbed by our bodies, and can possibly alter an unborn baby’s development. There is still little we know about this effect on human health. From the urine study, it’s clear some phthalates are more dangerous than others for hormonal development, but it’s also possible that other phthalates affect us in ways we have yet to measure. For example, we are still learning about how these and other chemicals interact with each other in our bodies. However, this study is extremely helpful, as it suggests we might find ways to avoid our current situation of increasing infertility, genital, and gender problems.

Final Thoughts

Parental concerns over any variation of inconspicuous penis are understandable. If there is any question regarding the size and health of a child’s penis, it’s important for pediatricians to first examine and measure, then clearly communicate to parents if the child’s penis is healthily formed and sized. Any questionable results should go to a pediatric urologist for a plan to ensure the health of the baby, and monitored with continued visits as the child grows older. In most cases, an inconspicuous penis is readily treatable. The vast majority of children with this condition go on to live happy, healthy, normal lives. 

References and Resources

Bianca S, Ingegnosi C, Ettore G. Maternal and paternal risk factors for hypospadias. Environ Health Perspect. 2005;113(5):A296.

Casale AJ. Concealed penis in childhood: a spectrum of etiology and treatment. J Urol 1999;162(3 Pt 2): 1165-8.

Reilly JM, et al. Small penis and the male sexual role. J Urol  1989;142:569-7. 

Van Seters AP, et al. Mutually gratifying heterosexual relationship with micropenis of husband. J Sex Marital Ther 1998, 14:98-107.

Van Wyk JJ, et al.  Should boys with micropenis be reared as girls? Journal of Pediatrics 1999; 134(5), 579-583.

Gillenwater JW. Adult and Pediatric Urology. Mosby Year Book; 1991.

Veale, D, et al. Nomograms for flaccid/erect penis length and circumference. BJU Int 2015, 115: 978-986.