When a person injects insulin in the same place for a long period of time, does the skin scar or harden over time?

Lipoatrophy: Repeated Insulin injections can leave unsightly swelling or even deterioration of the subcutaneous fat known as lipoatrophy. Furthermore, if Insulin is injected into areas where lipoatrophy is present, the absorption rate will vary, which will cause blood sugars to fluctuate.

Lipohypertrophy: It isn't really scarring. The fat cells under the skin get bigger and cause lumps to appear. These lumps interfere in the body's ability to absorb Insulin normally. Therefore, it is highly recommended to avoid using the same sites for most injections. If you develop lipohypertrophy, simply avoid giving Insulin in that area and it should clear up within several weeks.