Ever wonder why your penis is darker than the rest of your body? It's not just in your head: Whether your skin is black, white, or somewhere in between, genitalia and areolas naturally darken during puberty — "an effect of hormones," Dr. Shaunak Patel, a dermatologist from iCliniq, told Medical Daily.

When males go through puberty, their body produces more of the sex hormones adrenal and androgen. Androgen is responsible for secondary sexual characteristics, like facial and body hair; it also presents skin pigmentation. This happens when androgen responds to melanocytes, or the skin cells that produce melanin; resulting in a darker-looking groin and scrotum. As for our mouth and genital areas, the lips produce more pheomelanin — a reddish pigment found in redheads. This suggests that by simply looking redder, genitals also look darker.

Aside from puberty, another factor that can influence pigmentation, especially in the groin and scrotum, is friction. Dr. Lindsey Bordone, a dermatologist in the department of dermatology at Columbia University Medical Center (CUMC) in New York, told Medical Daily: "Skin thickens with chronic friction, so if there is chafing in an area, then over time a person will notice the skin has a tougher texture with mild darkening."

There are several medical conditions that can contribute to darker male genitalia, too. A hormonal or sugar imbalance — as seen in those with diabetes — can produce more pigment, according to Patel. Obesity can also produce dark skin in several areas, like the thighs and genitals, due to progressive rubbing of the skin. Lesser known conditions, like acanthosis nigricans, can lead to darkening of the skin on the back of the neck, the groin, and the armpits, according to the Mayo Clinic.

While a darker pigment is expected to be seen in the genitals, Patel does warn that "unusual blackish darkening could be an early indication for gangrene (Fourier's gangrene), or any thrombus obstructing the end arteries in the area."

So, if you see something unusual down there, it's best to consult your physician for further examination.