The common causes of knee rash are allergies, eczema, mosquito bites, etc., as follows: 1, if contact with allergic substances, the knee area with allergy symptoms, local rash, itching, scratching will appear small blisters, mainly allergies cause inflammatory exudation, it is recommended that the local use of mometasone furoate ointment for local application. 2, the knee area with eczema, there will be a rash, itching, flaking, crusting, oozing and other symptoms, The inflammation is better eliminated.