Macule: A flat spot or patch of skin that is not the same color as the surrounding skin.

Malignant When referring to cancer, malignant means the ability to grow and spread in an uncontrolled manner beyond the local confines of the tumor. Its opposite, "benign," refers to a growth that is non-cancerous.

Mastocytosis: Is characterized by infiltration of mast cells into the tissues of the body

Mast cells: Are connective tissue cells which release chemicals including histamine that are very irritating and cause itching, swelling, and fluid leakage from cells.

Melasmaalso: Known as chloasma or the mask of pregnancy, is a tan or dark facial skin discoloration. Although it can affect anyone, melasma is particularly common in women, especially pregnant women and those who are taking oral contraceptives or hormone replacement therapy (HRT) medications.

Melanoma Skin cancer that arises in melanocytes, the dark pigment cells of the skin. Melanoma usually arises in a pre-existing mole or other pigmented lesion. It is the deadliest form of skin cancer.