The skin will be especially red when slightly scratched, which may be related to skin allergy, artificial urticaria and other conditions. 1. Skin allergy: If the patient belongs to the allergic body, it is very easy to have an allergic reaction, especially after contacting some allergic substances, such as animal hair, pollen, willow, seafood and so on. After the allergy with a hand scratch, the patient’s local skin will have a congestive reaction, the formation of one or more red marks, there may also be a continuous piece of existence. 2. Artificial urticaria: The main manifestation is that after scratching the skin with fingers or other things, the skin in the area will quickly bulge, forming a red bulging line, and accompanied by itching sensation, and there will be no bulging line or air mass outside the scratch. Patients are advised to seek medical attention in time, and need to actively cooperate with the doctor for treatment after the cause of the disease has been diagnosed.