Freckle is a kind of brown dotted pigmentation spot commonly found on the face. The causes of sudden occurrence of freckle on the face include genetic factors and sunlight exposure. 1. Genetic factors: some people in the family often suffer from similar forms of freckles in the same area in several generations, and these patients with family aggregation may be related to autosomal dominant inheritance. 2. Sunlight exposure: sunlight exposure is a major acquired factor in the occurrence of freckles. Excessive exposure to sunlight or ultraviolet rays can induce freckles or cause their color to worsen. Patients with sudden onset of freckles should go to the hospital in time and receive standardized treatment under the guidance of specialists.