Itchy pinhole after insulin injection may be caused by local allergic reaction, needle infection, incomplete sterilization and other reasons. 1. Local allergic reaction: due to special allergies or allergy to the components of the drug, patients have an allergic reaction after injecting insulin, and redness, swelling, maculopapular rash accompanied by itching will appear in and around the injection site. 2. Needle infection: some patients do not change the needle in time during the injection process, and reuse the same needle when injecting, which can easily lead to infection and may cause itching at the injection site. When injecting insulin, you need to change the needle every time you inject to avoid infection. 3. Incomplete disinfection: When injecting insulin, incomplete disinfection or improper operation may cause local soft tissue infection, resulting in redness, swelling and itching at the needle hole. If there is itchy needle hole after insulin injection, it is recommended to consult a doctor in time, identify the cause of the disease under the guidance of a professional physician and take corresponding treatment program.