The need for blood tests to see a dermatologist is determined by the type of skin disease and the recovery of the skin disease, etc. Because there are many types of dermatological diseases, there are some that require blood tests to check the cause, the effect of medication, etc. There are also some milder skin diseases that do not require blood tests. Because there are many kinds of dermatological diseases, there are some dermatological diseases that require blood tests to check the cause and the effect of medication, etc. There are also some milder dermatological diseases that do not require blood tests.1. Blood tests are needed: when the dermatological disease is suspected to be caused by immune factors, blood factors, etc., such as systemic lupus erythematosus, arthritic psoriasis, allergic purpura, etc., the main purpose of blood tests is to find the cause and observe the disease process, etc. Severe folliculitis, scabies, etc. may require blood tests to observe the white blood cell index and see if systemic anti-infection treatment is needed; allergic skin diseases may require blood tests to find allergens. In addition, in the course of dermatological treatment, when using a certain drug, blood tests may also be performed to check the effect of the drug; 2. Blood tests are not required: general skin allergies, such as eczema, mild fungal infections and other lesions are only limited to a small area of the skin surface, generally do not need to draw blood for laboratory tests. Patients need to follow the doctor’s advice and improve the relevant tests in order to choose the most appropriate treatment method. When blood tests are needed, it should be clarified whether it is possible to eat or drink in the morning so as not to affect the test results.