If a melanocytic nevus is suspected of being a melanoma, it needs to be sampled or removed and sent for microscopic evaluation by a pathologist by a method called skin biopsy. One can do a complete excisional skin biopsy or a punch skin biopsy, depending on the size and location of the original nevus. Other reasons for removal may be cosmetic, or because a raised mole interferes with daily life (e.g., shaving). Removal can be by excisional biopsy or by shaving. A shaved site leaves a red mark on the site which returns to the patients usual skin color in about two weeks. However, there might still be a risk of spread of the melanoma, so the methods of Melanoma diagnosis, including excisional biopsy, are still recommended even in these instances. Additionally, moles can be removed by laser, surgery or electrocautery. In properly trained hands, some medical lasers are used to remove flat moles level with the surface of the skin, as well as some raised moles. While laser treatment is commonly offered and may require several appointments, other dermatologists think lasers are not the best method for removing moles because the laser only cauterizes or, in certain cases, removes very superficial levels of skin. Moles tend to go deeper into the skin than non-invasive lasers can penetrate. After a laser treatment a scab is formed, which falls off about seven days later, in contrast to surgery, where the wound has to be sutured.
Dysplastic nevus syndrome is a largely hereditary condition which causes a person to have a large quantity of moles (often 100 or more) with some larger than normal or atypical. This often leads to a higher risk of melanoma, a serious skin cancer. Dysplastic nevi are more likely than ordinary moles to become cancerous. Dysplastic nevi are common, and many people have a few of these abnormal moles. Having more than 50 ordinary moles increases the risk of developing melanoma.In the overall population, a slight majority of melanomas do not form in an existing mole, but rather create a new growth on the skin. Somewhat surprisingly, this also applies to those with dysplastic nevi. They are at a higher risk of melanoma occurring not only where there is an existing mole, but also where there are none. Such persons need to be checked regularly for any changes in their moles and to note any new ones. Sunlight
Ultraviolet light from the sun causes premature aging of the skin and skin damage that can lead to melanoma. Some scientists hypothesize that overexposure to UV, including excessive sunlight, may play a role in the formation of acquired moles. However, more research is needed to determine the complex interaction between genetic makeup and overall exposure to ultraviolet light. Some strong indications that this is so (but falling short of proof), are:

The relative lack of moles on the buttocks of people with dysplastic nevi.