For as long as I can remember, I’ve had a weird blue mole on my right hand. And for almost as long, I’ve been anxious that it’s not just a blue mole, but maybe, idk, cancer? But, thankfully no. Instead, my dermatologist tells me, it’s a blue nevus—a (usually harmless) type of mole that has a unique gray or blue color.
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Here’s what you need to know if you have one of these odd little blue moles.
What does a blue nevus look like?
A blue nevus has the shape of a classic brown or pinkish mole, but the color tends to be gray or blue, Shari Lipner, M.D., dermatologist at Weill Cornell Medicine and NewYork-Presbyterian Hospital, tells SELF. In some cases, it can be such a dark blue that it appears almost black.
These moles can be raised or smooth, and most people who have them only have one, though it’s possible to have more. Blue nevi also tend to be fairly small, “maybe one or two millimeters,” Dr. Lipner says. They look like the mark left behind from getting stabbed by a pencil, the grayish road burn caused by a scrape on asphalt, or radiation tattoos used in cancer treatment, she describes. They also tend to be more common in women than men, although it’s not really understood why.
What gives a blue nevus its color?
Their characteristic color is actually something of an optical illusion, Nada Elbuluk, M.D., clinical assistant professor of dermatology and director of the Skin of Color Center and Pigmentary Disorders Clinic at USC Keck School of Medicine, tells SELF. Normally, during embryonic development, the melanin-producing skin cells migrate to the top layer of your skin (the epidermis), Dr. Lipner explains. But if “the pigment doesn’t migrate all the way to the epidermis, it gets trapped in a deeper layer of skin,” Dr. Elbuluk says.
That forms a deep pocket of melanin that looks bluish to the naked eye thanks to something called the Tyndall effect, a term used in physics to describe the way certain types of matter (like fog or dust) scatter light. In fact, to diagnose a blue nevus, dermatologists often need to use a special tool called a dermatoscope, which is essentially a magnifying glass that shines polarized light on the skin. That allows you to see beyond the outer layer of skin and get a better glimpse at the true color and pattern of the mole, Dr. Elbuluk says.
In some cases, your dermatologist may need to biopsy a blue nevus just to make sure it’s not something more serious (like cancer). But Dr. Lipner says that biopsies are rarely required to diagnose a blue nevus.
What should you do if you have a blue nevus?
Because blue nevi can share some features of moles that might be skin cancer, it’s important to get them properly diagnosed.
This goes for any moles you have that might be considered an “ugly duckling,” meaning they look different from your other moles (as blue nevi usually do): If you have any moles that are asymmetrical, have an irregular border, uneven color, large diameter, or are changing in any way, have a dermatologist take a look.
Luckily, blue nevi very rarely become malignant. So having one shouldn’t increase your risk for cancer or change your usual skin cancer screening routine. Still, if you notice that it’s changing, itching, or bleeding, that warrants a conversation with your derm.
Unless your blue nevus turns out to be something more worrying, you don’t need to treat it, Dr. Elbuluk says, but some people do decide to have them removed for cosmetic reasons. Because the mole is so deep in the skin, though, completely excising it can be a more intense process than removing other types of moles, Dr. Lipner says, which is why she generally encourages people to keep their benign moles. “Instead of having the blue nevus that’s just a mark of you, you’re going to trade that for a scar,” she says.
But, ultimately, it’s up to you and your dermatologist. So if you have any questions, just talk to them.