Clinically, we can often hear patients v. After receiving photodynamic therapy to end the light avoidance period, photosensitivity reactions still occur, usually several existing photosensitizers require a light avoidance period of half a month to 1 month time, but some patients have different drug generation time, after the end of the light avoidance period still appear photosensitivity reactions, tips: photoallergy test after half a month or 1 month of light avoidance, that is, in a small area of the patient’s skin (such as the back of the hand or a small piece of the arm) Do a test to check whether the photoallergic reaction still exists. Cut 2cm×2cm holes with kraft paper, put the hand into the envelope after local exposure to sunlight for about 10min, and if the irradiated area does not show itching, redness and blistering within 24h, the sunlight time can be increased a little bit as appropriate. But 11:00-15:00 noon time period of strong light to avoid exposure to sunlight.