1. physical reaction. When people feel itchy, the skin is undergoing a physical reaction. Some epidermal cells falling from the skin and blood vessel wall cells falling from capillaries will have a physical reaction with bacteria, and an antigenic substance will appear.

2. This antigenic substance enters the blood through the communication of dermal capillaries, which leads to itching. When scratching the skin with your hand, it will stimulate the capillaries in the dermis, which will aggravate the itching.

3. Destruction of dermis. When you scratch your skin with your hands, you will damage the epidermis of your skin because of too much force. When people scratch the skin with their hands, the nerves in the dermis will be destroyed, which will also lead to inflammation. At this time, because the nerve is injured, it will send out the wrong instructions, reducing the impulse of the nerve. The brain's nerve control system accepts the wrong instructions, which will make the skin more itchy.

4. The existence of external bacteria. Scratching the skin with your hands will damage the outermost layer of the epidermis, thus exposing the epidermis directly to the air and contacting with various bacteria. At this time, the physical reaction will be more obvious.