UVB phototherapy is a proven method for treating psoriasis, vitiligo and other skin diseases. However, because of the great individual differences in the human body, and even the sensitivity of the same individual to UVB at different stages of treatment can change, the starting irradiation dose must be determined for each patient’s light responsiveness, and the response to treatment after the last irradiation must be verified before each new irradiation dose is determined. The starting dose of UVB therapy is determined by the physician in charge prior to treatment, based on the patient’s skin type or on the patient’s measured minimum UVB erythema and minimum phototoxicity. The starting dose of UVB therapy is usually 50-75% of the minimum erythemal volume, 3-5 times per week. Whether the dose is increased with each successive treatment and the rate of dose increase are determined by the frequency of treatment and the response to treatment. In principle, the increase in dose should be sufficient for the appearance of freshly visible erythema after each irradiation. When combined with other therapies such as retinoic acid and calcipotriol, the dose and frequency of irradiation should be adjusted. The skin of the lower legs, feet, palms and elbows is generally less photosensitive than other parts of the body and the dose can be increased appropriately when irradiated. Treatment is generally continued until the disease is in complete remission or until there is no further improvement after continuous treatment. The treated area should be protected from excessive sunlight after the treatment is completed. If a patient shows signs of phototoxic reactions or photomorphic reactions during treatment, attention should be paid to whether there has been additional exposure to sunlight, whether photoprotective agents have been discontinued, or whether other photosensitizing medications have been taken. In addition, some cosmetics, fragrances in cleaning products, vegetables, and tea for laxatives may contain photosensitizing substances. Short-term adverse reactions after phototherapy are generally the same as those from excessive sun exposure and include erythema, edema, and occasionally blistering. Once they occur, they can be treated with a number of medications in addition to adjusting the dose of exposure or suspending treatment.