A white patch on the legs may be caused by lichen planus, vitiligo and pityriasis alba. 1. lichen planus: malassezia infection may cause abnormal skin pigmentation, resulting in a white patch on the legs, as well as localized itching, flaking and other symptoms. 2. Vitiligo: it is an acquired factor caused by subcutaneous melanin loss, can cause skin white spots, clear boundaries, smooth surface, may also cause the phenomenon of a piece of white on the legs. 3. white chaff rash: the cause is unknown, may be related to infectious factors, malnutrition, dry skin, sun exposure, will cause the border is not clear, round or oval hypopigmented spots, so it may lead to a piece of white on the legs. There may be other reasons for a white patch on the leg, and you need to go to the hospital in time to check and clarify the cause of the disease.