Repeated injection of insulin into the same injection site can cause lumps to form in the skin. This 'lipohypertrophy' occurs as a result of the local anabolic effect of insulin on subcutaneous fat, which makes it grow more, usually appearing as lumps.

They can make it more difficult for injected insulin to be absorbed.

Injection sites should be inspected and rotated regularly. Insulin should also not be injected into oedematous (fluid filled) areas as this can be a barrier to subcutaneous absorption into blood vessels.

It has also been noticed that injection of insulin through a layer of clothing can be associated with local bruising.