A summer vacation often means fun in the sun and water, but it can also mean an increase in the chances of developing a dangerous mole. Most kids are born without moles, called "nevi" by dermatologists, but a recent Colorado study of 681 white children found that every beach vacation leads to a five percent increase in small moles on children's skin. "The development of new moles is of concern, because the higher the number, and the more irregular moles, the greater the risk for developing melanoma, the most dangerous of the skin cancers," says Dr. Josh Fox, founder and director of New York and New Jersey-based Advanced Dermatology P.C. "Melanoma occurs relatively infrequently, accounting for about three percent of skin cancer cases, but it causes about 75 percent of skin cancer deaths. Prevention is the best route to lowering your child's risk of the disease." Most moles are not dangerous, assures Fox, but it is important to monitor any that appear on your child's skin and track the number, shape, color and symmetry of them from year to year because melanomas can grow in or near moles. In fact, the appearance of a new mole or a change in the size, color or shape of a mole is often the first sign of the cancer. Normal Moles Simply put, moles are pigmented cells that cluster together. They can be brown, tan, pink or flesh-colored, and are usually oval or round and about the size of a pencil eraser. They typically appear during childhood, adolescence and early adulthood, and they can develop anywhere on the body. They will often get bigger with age, get darker or lighter, develop a raised surface or sprout hair. "By the time most people reach adulthood, they have between 10 and 40 moles," says Fox. Some people have a genetic tendency toward developing moles and also malignant melanoma. Those who have fair freckled skin and who work or spend a lot of time outdoors are more likely, due to sun exposure, to have moles that develop into skin cancer. Only about one percent of infants are born with a mole, which is known as a "congenital nevus." These moles can look like normal brown, tan or pink moles or they can look like a blue-grayish bruise. A congenital nevus is typically harmless, according to Fox, unless it is really large (bigger than eight inches), in which case it increases the risk of developing melanoma over the first five or ten years of life by as much as 10 percent. They are called a precancerous lesion and must be followed. What Dangerous Moles Look Like The cardinal signs of potentially malignant moles are ones that: Have an irregular shape (asymmetric) Have jagged edges Are uneven in color or shape Have red areas Are larger than the size of a pencil eraser Are growing rapidly Want to read more? Subscribe to one of our monthly plans to continue reading this article.