F1000 Commentary: Treatment of adults with complications from previous hypospadias surgery / What is “micropenis”?

“Micropenis” is a medical term typically today applied when the length of a penis, when the penis is stretched, is at least 2.5 standard deviations smaller than the average penis length when stretched. (The reason we use “when stretched” is because there is a lot of variation from male to male between flaccid penis length and erect penis length. The “when stretched” length measurement is an attempt to standardize the measurement of penises.) By this definition, men and boys whose penises fall in the smallest 0.6% (smallest 6 in a sample of 1000) are said to have the condition “micropenis.”

In practice, some medical texts have defined micropenis in newborns as involving stretched penis lengths of 2.5 centimeters (about 1 inch) or less. Other texts say the definition of micropenis is newborn stretched penis lengths of 1.9 centimeters (about 3/4 inch) or less.

Sometimes adults are surprised at how small baby boys’ penises look, because adults are used to seeing adult male genital proportions, not infant male genital proportions. So newborn boys often look to adults like they have smaller-than-average penises even when they in fact have average-sized penises.

The penis typically grows relatively more than the rest of the body at puberty. That is because the tissue of the penis is very sensitive to the hormones that surge during the typical male puberty. So the big hormonal shift that happens at the typical male puberty usually makes the penis grow more than the rest of the body. How much the penis will grow at puberty varies in males and is not easily predicted.

Sometimes obesity can make a boy or a man appear to have a smaller penis than he really does. This is because the surrounding fat of the abdomen makes the penis project outward from the body less than it otherwise would.

Micropenis can be caused by a number of different conditions. Figuring out the cause requires a series of medical tests.

Posted in: Specific Conditions

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