The abdomen is the most common site for injecting insulin. For some people, this site is not suitable, and other sites must be used. These include the upper arms, the upper buttocks and the outside of the thigh. All of these sites are most effective because they have a layer of fat to absorb the insulin better. This process directly injects insulin into the subcutaneous tissue. These areas also have fewer nerve endings, meaning that they are the least painful areas in which to inject.
Some diabetics use different sites for different types of insulin injection. Insulin is absorbed differently through the various injection sites. Some sites are better for rapid absorption (abdomen), whereas others are better for slow absorption (thighs, hips.). Injections should be moved around in one area, changing sites completely once every week or two. Make sure that each injection is an inch and a half away from the last one. Use the same area for at least a week, and be aware that the injection site will affect blood sugar levels