From the classically chic beauty mark that delicately graced the cheek of Marilyn Monroe to the constellation of moles that scatter across some people’s backs, these brown spots can be found on almost anyone’s body. They are caused by clusters of pigmented cells, called melanocytes, which form in part due to their exposure to UV light. Though adults typically have anywhere from 10 to 40 scattered across the body, individuals with lighter skin tend to have more.

READ MORE: What Causes Moles?