Psoriasis is a nickname for psoriasis, and the people are more familiar with the name psoriasis than psoriasis. However, clinically, doctors will call it psoriasis, but the two are the same thing. We talked about phototherapy for psoriasis earlier, and many people are inquiring if they can be phototherapy? To know this, let’s do an exclusion method to see when phototherapy cannot be performed! What conditions can not be phototherapy? The following cases are absolutely not phototherapy. ① Patients with epilepsy or lupus erythematosus and other diseases are not allowed, because phototherapy can induce lupus erythematosus, epilepsy and other diseases. ②Patients suffering from photosensitive dermatitis or allergic to light, the disease will be aggravated by light exposure. ③Light therapy is not allowed during taking photosensitive drugs, such as retinoids, antibiotics like quinolones, ashwagandha, tetracycline and other conditions. (4) You should not take phototherapy when you are suffering from melanoma, basal cell carcinoma and squamous cell carcinoma of the skin. In addition, photosensitive foods such as mud snail, celery, ashwagandha, parsley, and heavily scented wild vegetables should not be consumed during phototherapy. There are also some cases where phototherapy should not be performed as much as possible ① Suffering from malignant tumor, although phototherapy does not have much effect on visceral tumor, it is not recommended to perform phototherapy. ②Patients who cannot cooperate with phototherapy, such as patients who cannot stand and stay in the phototherapy chamber, patients who are too old and weak to stay in the phototherapy chamber, children with claustrophobia, etc. For patients with special physical conditions, doctors have to analyze each case on a case-by-case basis. Do I need phototherapy when other treatments are already effective? For patients whose disease can be controlled by topical medications and who only occasionally relapse, the combination of phototherapy can enhance the efficacy and inhibit relapse. When the efficacy of topical medications is poor, topical phototherapy can be used to relieve the disease and serve the purpose of treatment. When the lesions are large and the efficacy of topical drugs is limited, combining phototherapy can enhance the efficacy. Therefore, the purpose of using phototherapy is different for different patients with psoriasis. What is the effect of phototherapy? How long can it be maintained without relapse? The therapeutic effect of phototherapy is certain. 70%~80% of patients can achieve 70%~80% remission after 2~3 months of regular treatment. The length of time that can be maintained without recurrence after phototherapy depends on the patient’s specific situation. Patients with milder disease can be maintained for several months without recurrence; patients with stubborn and difficult to clear disease have a higher risk of recurrence and may have new lesions 2~3 months after stopping phototherapy.