Lipohypertrophy is a thickened, enlarged or raised portion of skin's fatty underlayer where insulin injections are given. It's a kind of lipodystrophy. Continuing to inject into the same area can be one cause of this; the need to alter injection techniques can be another. Changing or rotating the site one injects insulin is a good way to prevent lipohypertrophy and lipoatrophy, as well as preventing possible absorption problems. Insulin does not absorb well from these thickened areas.