Hair a day without washing is very oily can be seen in normal people, but also may be seborrheic dermatitis, ringworm and other diseases caused by, should be timely medical care, clear cause of treatment. 1. physiological situation: normal people in a long time to stay up late, frequent hair washing, emotional upset when the hair a day without washing is very oily, this kind of people should keep the mood of pleasure, appropriate physical exercise, generally do not need special treatment. 2. seborrheic dermatitis: hair a day without washing is very oily may also be caused by seborrheic dermatitis, the patient will also have the head of erythema papules, flaking, itching, etc., you can use tacrolimus, ketoconazole, etc. for treatment. 3. Tinea capitis: Tinea capitis caused by dermatophytes infecting the skin of the head can also cause the hair to be very oily when not washed for a day, and the patient will also have one or more alopecia patches accompanied by scaling, hair breakage, etc., which can be treated with ashwagandha and so on. All of the above drugs should be used under the guidance of a doctor.