blue nevus [OFr, blou + L, naevus, mole] , a sharply circumscribed, usually benign, steel blue skin nodule with a diameter between 2 and 7 mm. It is found on the face or upper extremities, grows very slowly, and persists throughout life. The dark color is caused by large, densely packed melanocytes deep in the dermis of the nevus. Nodular blue nevi found on the buttocks or in the sacrococcygeal region occasionally become malignant. Any sudden change in the size of such a lesion demands surgical attention and biopsy. Compare melanoma.
