A small itchy rash on the back of the foot may be tinea pedis, eczema, mosquito bites caused by, should consult a doctor in a timely manner, clear the cause of the corresponding treatment. 1. Tinea pedis: the back of the foot a strange itchy rash may be caused by fungal infections caused by tinea pedis, such people will also have the soles of the feet of the flaking, cracking, keratinization, can be used externally ketoconazole, sertaconazole, etc. for treatment. 2. Eczema: Eczema can cause oozing, erosion, flaking, itching and rash on the back of the feet, etc. Scratching should be avoided, and topical hydrocortisone butyrate and tretinoin acetate cream can be used for treatment when necessary. 3. Mosquito bites: If there is itching and small red rash on the back of the feet after going to the woods or lawn, it should be considered to be caused by mosquito bites, and should avoid scratching, which can be cured after a few days, or topical glycerine lotion can be used. All of the above drugs should be used under the guidance of a doctor.