This came up in a thread by Drywallstar and ANBRO suggested I do a write-up, as it seems some fellas have complained of this.

Lipohypertrophy is a medical term that refers to a lump under the skin caused by accumulation of extra fat at the site of many subcutaneous injections of insulin. It may or may not be mildly painful. This is usually seen in diabetics, as insulin exerts a hypertrophic effect on adipose cells. That is, it causes the enlargement of the fat cells in the immediate vicinity.

Although this is normally caused by insulin, there is evidence in the literature that it is can be caused by hGH.

http://www.ncbi.nlm.nih.gov/pubmed/11957429

As well as anecdotal evidence from bodybuilders who have experienced this. Now, I don't see it being related to the iGF release, because that comes from the liver, far from the injection site. The GH itself must also exert a hypertrophic effect on adipose cells. Which doesn't seem too far-fetched. I do believe that injecting iGF could also cause this because obviously, it's a protein with high sequence similarity to insulin.

To avoid lipohypertrophy, persons who inject insulin / hGH / iGF daily for an extended period of time are advised to rotate their injections among several areas (usually upper, outer arms, outer thighs, abdomen below and around the umbilicus, and the upper parts of the buttocks

Lipohypertrophy usually will gradually disappear over months if injections in the area are avoided.And if your bodyfat is above a certain level, you probably won't even notice them. This was the case with Drywallstar, as they only became apparent as he became leaner.

So maybe this will help to put some brothers' minds at ease in the future if they notice these bumps. Now of course, there could be other things too, like an allergic reaction, particularly if there is redness or itching associated with it. But this is just a good thing to add to your general knowledge.