What is skin cancer?The NHS says there are two types — melanoma and non-melanoma.MelanomaA new mole or a change in the appearance of an existing mole is frequently the first indication of skin cancer.Normal moles are typically round or oval, have a smooth edge, and have a diameter of no more than six millimetres.However, size alone does not always indicate skin cancer. A cancerous mole can have a diameter of less than 6mm, and a healthy mole can be larger than this.