For some reason, many people don’t seem to treat skin cancer with the same level of seriousness as they do other cancers—they hit the tanning beds, or go out to the beach with no sunscreen, and assume they’ll be okay. But the reality is, skin cancer is a serious disease—just ask Tawny Willoughby, whose photo of her skin cancer scars recently went viral. It’s also a common disease: according to the Skin Cancer Foundation, it’s the most common cancer in the world, with upwards of 13 million cases diagnosed every year, and the numbers are growing. The good news? It’s also the most preventable cancer. Ninety percent of nonmelanoma skin cancers are associated with ultraviolet radiation exposure from the sun, and the risk of developing skin cancer doubles if you’ve had more than five sunburns. So taking simple measures to limit sun exposure, avoid tanning beds completely, and use broad spectrum (UVA/UVB) sunscreen with an SPF of 15 or higher, can help immensely.

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Early detection is also key, which is why the Skin Cancer Foundation recommends you do monthly head-to-toe self-exams of your skin. The more familiar you are with your skin at “baseline,” the more likely you are to notice if anything is out of sorts. If you’re able to find harmful lesions, moles, or spots early, there’s a good chance they can be removed and cured. So how do you tell a normal mole or spot from a possibly cancerous one? According to the American Cancer Society, you can use the alphabet—or at least the first five letters—to remember the key signs of melanoma. The ABDCE rule consists of the following characteristics that can be skin cancer signifiers:

A for Asymmetry: Your mole or birthmark should be consistent in its own characteristics—if one half is a different color or shape, for example, than the other half, you should inform your doctor.

B for Border: Look out for edges of moles that are ragged, irregular, notched, or blurred. If you have a mark with those traits, it could be cause for concern.

C for Color: Normal moles are evenly colored (in brown, tan, or black). If your mole shows any pink, red, white, or blue, or if the color is not even or consistent throughout, consult your doctor.

D for Diameter: The general rule of thumb with mole sizes is that, if they’re less than 6 millimeters across, or about ¼ inch, they’re probably safe. Moles larger than that may be melanomas. That said, this is isn’t a hard and fast rule, so if you have a mark that’s less than ¼ inch but shows any of the other symptoms on this list, it’s a good idea to get it checked out just in case.

E for Evolving: Moles usually appear at some point during childhood or adulthood, and after they develop, they don’t change much. The appearance of harmful moles, on the other hand, may change over time, whether in color, size, or shape. Take an inventory of your moles every once in a while so you’re familiar enough with them to recognize a change when it occurs. A couple minutes every month could be invaluable in the long run.

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Though the ABCDE rule covers many of the most common signs of skin cancer, it doesn’t represent every symptom. If you experience any of the below symptoms, either on their own or in conjunction with the aforementioned ones, give your doctor a call:

  • Sores that don’t heal (one or multiple)
  • Pigment spreading outside the border of a spot and onto the surrounding skin
  • Redness or swelling outside the border of a spot or mole
  • Change in feeling of the spot—perhaps by becoming more painful or sensitive, or becoming itchy
  • Change in the surface of a mole: Does the texture feel different? Is there anything coming out of it? Did it go from being flat to raised (or more raised than it was)?

Admittedly, all of these symptoms can sometimes be a bit difficult to notice or detect. Aside from regularly examining your skin, err on the side of caution. If you see or feel something out of sorts, go with your gut and call your doctor. You know your body better than anyone else, and if there’s something that makes you pause, it’s best to get it looked at just in case.