In general, dark patches on calf skin may be pigmentation, traumatic scarring and allergy. 1. Pigmentation: It may be due to some congenital or acquired reasons, such as sun exposure, chemical stimulation, etc., resulting in localized pigmentation of the skin of the calf, thus causing the manifestation of dark patches on the skin of the calf. 2. Traumatic scar: some patients with keloid body have small keloid scars after small bumps on the legs, which, together with melanin pigmentation, lead to the manifestation of dark plaques on the skin of the lower legs. 3. Allergy: due to contact with certain substances that cause allergy to the calf skin, resulting in skin allergy phenomenon, may be due to scratching and other reasons for the formation of spots, thus appearing the phenomenon of black patches of calf skin. There are many other reasons that can lead to the phenomenon of dark patches on the skin of the calf, it is recommended that the patient go to a regular hospital, consult a professional doctor, complete the relevant examinations, identify the causes and then standardize the treatment under the guidance of the doctor to avoid blind treatment.