A junctional nevus, sometimes called a mole, is a type of benign, or non-cancerous, skin growth. It is typically dark brown, flattish and rounded in appearance. There are a number of types of nevus, plural nevi, originating from different layers of the skin, and the cells that form a junctional nevus are situated around the junction between the epidermis, or outer layer, and the dermis below. Although junctional nevi are not cancerous in themselves, it is important to notice any changes in their appearance, because there is a small risk that they can transform into a type of skin cancer known as a malignant melanoma.

Junctional nevi are members of a group of moles called melanocytic nevi. Melanocytic nevi are made up of cells known as melanocytes. Melanocytes make melanin, a pigment that provides the skin with its color, and where they cluster together the skin looks darker, giving a junctional nevus its typical appearance.

A junctional nevus can appear anywhere on the skin, and may arise throughout life, although as people get older fewer are produced, and existing nevi also tend to disappear. The number of junctional nevi present on the skin of one person can vary, from a handful to several hundred, and they are generally more common in people with fair skin and those who have been exposed to the sun during childhood. Junctional nevi are usually fairly small, typically up to just over a quarter of an inch (around 7 mm) in size, and the color can be anything from light brown to brown-black. While each junctional nevus typically has only a small risk of changing into a malignant melanoma, for some people, who have relatives with the cancer, that risk is increased.

Signs that a junctional nevus might be changing to become malignant, or cancerous, include instances of itching, pain or bleeding, alterations in the shape or color, especially where symmetry is lost or edges become irregular, and variations in size. Occasionally, rather than becoming malignant, a junctional nevus may turn into what is called a compound nevus. Compound nevi typically stick up above the surface of the skin slightly more than junctional nevi, but their overall size is similar. There may be variations in color, with darker areas found in the center, but their appearance is roughly symmetrical. Compound nevi are typically benign growths requiring no treatment.

If a junctional nevus, or any mole, show signs associated with possible malignant change, it should always be checked by a doctor. When a malignant melanoma is suspected, the usual treatment is to cut the mole out completely before examining it under a microscope. Where no evidence of cancer is found, no further treatment is needed. If malignant melanoma is diagnosed, the outlook depends on how far it has progressed. In cases where the melanoma has been removed before it has spread, a cure is possible.