Pigmented moles and malignant melanoma have become a growing concern in recent years, and every day in the clinic, people inquire whether their pigmented moles are malignant. In fact, the most common method used by dermatologists is the so-called “ABCD” rule, through which experienced dermatologists can effectively identify many early malignant melanomas. The so-called “ABCD” stands for four kinds of manifestations: A (asymmetry) asymmetry: the mole is arbitrarily divided into two from the center, benign nevi are usually symmetrical on both sides; while malignant melanoma is often asymmetrical. B (border): usually the border of benign nevus is clear and smooth, while the border of malignant melanoma is uneven and jagged, and some borders and the surrounding normal skin show gradual changes and are not clear. C (color): ordinary nevi usually have only one color, often brown, brown or black, and the color is uniform; while malignant melanoma is often mixed with many colors, including brown, black, red, white, blue, etc., which are irregularly distributed in the skin lesions. D(diameter): usually the diameter of benign nevus is less than 6mm, but some congenital nevus will be bigger; while malignant melanoma is often bigger than 6mm, especially if it suddenly increases to more than 6mm in diameter. If a nevus shows the above changes, it should be concerned, and go to the hospital for consultation if necessary. Besides, if a pigmented nevus suddenly becomes itchy, painful, red, swollen, uneven, ulcerated, bleeding, with satellite-like “small moles” around it, or with enlarged lymph nodes in the area, you should go to the hospital and ask a professional dermatologist to help you diagnose it. Even experienced dermatologists can hardly distinguish some moles and melanoma with naked eyes or even dermatoscopy, so they should take biopsy of suspicious lesions in time and make clear diagnosis through pathology. The important thing for malignant melanoma is early detection, early diagnosis and early treatment. Although the incidence rate of Chinese people is much lower than that of European and American people, so we don’t need to be overly panic, but we shouldn’t take it lightly, pay attention to the changes of our own skin, and consult the doctor in time when there are suspicious changes, so that we can prevent the disease from occurring before it is too late.