It’s hard to resist the temptation of the summer sun. For one, you’ve gotta show off your gym progress. (After all, half the reason you work out is to have a great beach physique.) On top of that, all that sun is good for your mood—and tanned muscles look damn great, too.

But, by now you also know that increased sun exposure—especially without UV protection—leads to cellular mutation. With that tan comes freckles, burn, harmless moles, and, in severe cases, melanoma (cancerous moles).

We don’t want to be total buzzkills toward your sunny disposition, but it is important to know how to protect yourself from these extreme side effects—as well as how to “read” your moles, to determine which ones require more immediate professional attention. We sought expertise from one of our most trusted dermatologists, Jane F. Kardashian, M.D., of Fresno, CA. Kardashian is a fellow of the American Academy of Dermatology, and she gave us some damn good advice on how to protect our hides—actively and proactively.

Why moles happen

A mole is a cluster of pigment. More specifically, it’s a (usually) harmless gathering of melanocytes, which are the cells producing said pigment. They’re usually the result of sun exposure, and Kardashian says that their prevalence is related to age, race, genetic, and environmental factors: “Very few melanocytic nevi (the technical term) are present in early childhood,” she says. “But there is a period of rapid development at puberty. In general the highest numbers of nevi are observed in individuals aged 20-29.”

It’s no surprise that nevi become more prominent when you don’t protect yourself from the sun’s harmful UVA and UVB rays (ditto for tanning beds).

“Failure to cover up with clothing or apply sunscreen with frequent reapplication will increase your risk of developing more moles and melanoma (skin cancer),” says Kardashian. “This is particularly true if you are at a location with a higher altitude, at the beach or snow.”

When are moles dangerous?

Kardashian outlines 10 instances in which you should seek immediate attention—that is, when the nevi might in fact be the more severe, life-threatening melanoma.

1. Color bariance: Either a drastic change in color or inconsistent color, such as combinations of tan, white, red, pink, brown, black, or gray.

2. Other morphing: Moles changing in any way, such as shape, height, or surface texture.

3. Blurred lines: Any that have a nebulous, scalloped, or irregular border.

4. Agony: A mole that is painful or exudes fluid or blood.

5. Behemoths: Moles greater than 6mm (1/4") in width or gradually growing in size.

6. Asymmetry: When both sides of a mole don’t match one another, when folded in half.

7. Sores: Any skin abrasions that do not heal, regardless of treatments.

8. Texture: Surface changes such as scabbing and scaling.

9. Mega moles: They’re called “dysplastic moles,” and are usually characterized by larger size, blurred borders, and variations of different colors (red, tan, brown, and black). Kardashian says the appearance of these moles can double your risk of melanoma.

10. Bloodlines: A history of melanoma in a first-degree relative (parents or siblings).

Adds Kardashian, with urgency: “Melanoma can grow quickly. In as little as six weeks it can become life-threatening. If left untreated, melanoma can spread to other parts of the body, usually through the lymphatic system to the various organs, when it can be fatal.”

When are moles harmless?

“There are several types of harmless, acquired melanocytic nevi,” Kardashian says. These include:

1. Junctional melanocytic nevi: Flat, mid-to-dark brown, and circular in shape. (“In childhood, most moles are junctional,” says Kardashian.)

2. Compound melanocytic nevi: Raised, brown bumps. They can have a warty surface and hairs growing from them.

3. Intradermal melanocytic nevi: Raised, often hairy bumps that are pale in color.

4. Blue mevi: Located deeper in the skin, and have a blue cast due to the light’s reflection.

5. Halo nevi: A mole surrounded by a pale ring, which may gradually go away by itself.

Kardashian warns, however, that an increase in these harmless, “precursor” nevi can also increase the odds of developing melanoma. In fact, “one-third of melanomas are associated with nevus remnants,” she says. Bottom line: Get your skin checked, nevertheless.

The melanoma removal process

To remove any melanoma from the skin, you must first remove the mole itself. Kardashian says that most surgeons follow guidelines set forth by the National Institutes of Health and American Academy of Dermatology: “Depending on the tumor’s depth of penetration into the skin, as little as half a centimeter will need to be excised, or as much as 2cm beyond what can be seen by the naked eye.” After this procedure, you’ll have stitches for one or two weeks, and you can minimize or prevent scarring by following the doctor’s recovery plan.

How to stay proactive against moles

You must put two equally important habits into practice: First, schedule annual skin exams—starting yesterday. These should begin after puberty, especially if an immediate relative has any history of melanoma. (In this case, kids and adults should get checked every six months, starting at age 10.)

Secondly, be smart about your time in the sun. Wear sunscreen (Kardashian suggests SPF 30 or greater, with zinc oxide or titanium) as well as protective clothes, hats, sunglasses—anything, basically, that shields you from the sun. Staying in the shade is especially imperative between 11 a.m. and 3p.m., when the sun is most directly overhead and rays are strongest. Apply sunscreen 15 minutes before going out in the sun, and immediately after swimming and towel-drying, or every two hours otherwise, she says.

And remember: If you’re even curious about anything surprising you notice on your skin, talk to a dermatologist. Being proactive is your best defense.