Skin growths in and around a patient's armpit. These skin growths are epidermal naevi, and are due to the overgrowth of the epidermis layer of the skin, caused by a birth defect. Usually, the epidermal naevi form a line (linear) on one side of the body (unilateral), hence linear epidermal naevi is also called naevus unius lateralis. The skin defect can cause disorders in other internal organs, and this is then called epidermal naevus syndrome. The growths can become malignant, but this is rare. There is no effective treatment, but Calcipotriol, a vitamin D derivative, can reduce the excessive skin growth. Photographed in Africa.