1, dosage: Do not use too much, the usual amount can be calculated according to “fingertip unit”, a fingertip unit refers to the amount of ointment or cream from the 5mm diameter tube extruded from the tip of your index finger to cover the first interphalangeal joint. Scalp generally use 3 fingertip units, a side of the lower limbs and feet need 8 fingertip units, the front and back of a hand need 1 fingertip unit. 2.Frequency: not the more times the more effective, generally 1-2 times can be used for common topical preparations, some drugs only need to be applied at night because of the sensitivity to sunlight, such as Adapalene, peroxymethylphenidate, anti-spot whitening milk, etc. 3.Side effects: Topical drugs are not absolutely safe. Some patients have allergic reactions because of strong sensitivity to drugs. Dermatitis occurring on the face should be particularly alert to the side effects of topical medications because of the inflammatory state or the change of skin barrier function. It is recommended that it should be tried on a small scale and expanded to the entire range of lesions on the face after a few days. Common side effects are redness, swelling, flaking and other discomforts, which should be followed up by a doctor promptly when they occur. P.S.: Wet compress method: Wet 8 or so layers of gauze pads with the medication solution, take out and wring out the water slightly, so as not to drip, and put on the lesions for 20-30 minutes or more, which can be changed in between, 1-2 or more times a day.