Moles can appear at any time during your life. You might be born with a mole (or a few moles, and these are known as congenital moles) or you might find you don't see your first one appear until long after you've had a kids of your own. By the time we reach adulthood, though, almost every person has at least one mole.

The lighter your skin tone, the more likely you are to have multiple moles -- having just a few moles on your body is totally normal for most people, but light-skinned individuals may find they have more, as many as 10 to 40 moles [source: American College of Dermatology]. But even a few dozen moles scattered on your body doesn't mean anything is wrong or that you'll develop skin cancer. Common moles, sometimes also called beauty marks (or nevi to your dermatologist), are, for the most part, harmless to the 300 million people who have them [source: National Cancer Institute].

But about two out of every 10,000 Americans develop melanoma each year, though, and it's important to know the signs of a mole gone bad [source: National Cancer Institute].

Even when they are benign, common moles don't always look the same -- no two moles look alike, even on the same person. Typical moles appear round, flat (or slightly raised) and are one color. Though you'll frequently see moles that are brown, they can also be the same color as your skin tone or black, tan, red, pink or, yes, blue. They can also be colorless. Some moles are hairy. And they can grow on any part of your skin, from arms and legs to other trickier places like your palms, under your fingernails or on your scalp [source: American College of Dermatology]. This is all normal in the world of moles.

What's abnormal is when a mole begins to change.

Skin cancer screening begins with you, at home, with your ABCs. Well, your ABCDEs, to be more accurate. The ABCDEs are your checklist for assessing any changes in your moles.

It's recommended we all do a head-to-toe monthly mole check for the following clues that our moles may be changing or may need additional examination by a health care professional:

A mole that is asymmetrical, has irregular borders, changes in color, has a diameter larger than a pencil eraser (the form of skin cancer known as melanoma often appears larger than 5-6 millimeters in diameter) may indicate that it's a mole may need to be biopsied. Look out for moles that seem to be evolving since the last time you evaluated them, have changed in appearance, become itchy, scaly or tender, or ooze or bleed. Have your doctor examine these types of moles[source: WebMD].

In addition, a regular tanning habit (and a history of sunburns), having more than 50 moles and a family history of skin cancer, all increase your chance of developing melanoma [source: National Cancer Institute]. While it's important to remember most moles begin and remain benign, regular and frequent evaluation of your moles, especially any new moles you notice, can make the difference when it comes to catching cancer early.

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