Insulin injection is a relatively safe treatment for the body, and the common harmful effects may be as follows: 1. Allergic reactions: people who are sensitive or allergic to insulin may have local itching and hard nodules on the skin after insulin injection, and serious cases may induce allergic reactions throughout the body, which are relatively rare. Light cases can be desensitized, and heavy cases are recommended to stop insulin injection or change the type of insulin; 2. Water and sodium retention: If insulin is injected too much, there may be water and sodium retention, which leads to edema of the face and lower limbs and accumulation of abdominal fat; 3. Abdominal obesity: If the amount of insulin is injected more and insulin is injected for a long time, it may lead to the occurrence of abdominal obesity, and fat may appear at the injection site The accumulation of fat may appear at the injection site, and the weight is found to increase significantly with the increase of insulin injection dose. Usually because insulin has the role of promoting synthesis, and lead to the occurrence of body obesity; 4, hypoglycemia: injection of insulin to the body’s greatest danger is the adverse effects of insulin that is hypoglycemia, if the use of insulin improper, such as too much or injection timing is not right, or after the injection of insulin did not eat in time, may lead to the occurrence of hypoglycemia, serious cases may be life-threatening as well as coma. So overall, insulin is relatively safe for human body, but we should pay attention to grasp the amount, as well as the method and manner of injection.