The severity of a pigmented nevus with a diameter of 1 cm depends on the location of the growth and the pattern of the rash, as well as the self-perceived symptoms, and you should go to the dermatology department of the hospital in time to determine the condition. Nevus pigmentosus is a kind of benign skin growth, most people will have some nevus pigmentosus in their adult life, and these nevus pigmentosus usually do not have any effect on the body. Nevus pigmentosus has a low risk of malignancy, and nevus pigmentosus with a diameter greater than or equal to 1 centimeter is a relatively large nevus pigmentosus. The risk of malignancy is higher if the nevus is located on the genitals, palms of the hands and feet, or underneath the fingernails of both men and women. Before a pigmented mole becomes malignant, there are usually some signs, such as a sudden increase in size within a short period of time, deepening of the color, redness of the skin around the mole, itching or tingling sensation of the local skin, etc. The above symptoms are more serious. The appearance of the above symptoms is a more serious pigmented nevus, which needs to go to the hospital in time for excision and treatment, and do pathological examination if necessary.