Dullness of skin color around the corners of the mouth may be caused by perioral dermatitis, post-inflammatory hyperpigmentation, chloasma, and fixed medicinal rashes. 1. Perioral dermatitis: frequent use of hormone-containing cosmetics may induce melanocytes over time, leading to local inflammatory papules, redness or deepening of pigmentation. 2. Post-inflammatory hyperpigmentation: If the local eczema or allergic dermatitis has occurred before, the post-inflammatory hyperpigmentation is left after the treatment, leading to the deepening of the local color. 3. Melasma: Melasma usually occurs on the face, and if it involves the perioral area, it will lead to deepening of local color and darkening. 4. Fixed drug rash: taking certain drugs, such as sulfa drugs, antipyretic and analgesic drugs, if allergic to the ingredients in the drugs, causing fixed drug rash, which may lead to perioral or other parts of the pigmentation. It is recommended to do a good job of local care, strict attention to sun protection, if necessary, to the hospital dermatology department to find the cause, symptomatic treatment.