The following article was written by Southern Ghost
This comes from high BA content usually >2% BA. High amounts of BA are used to make up for poor production methods and using non sterile equipment. To prevent the end user getting an infection the brewer will simply dose up the BA content to compensate. This will lead to post-injection pain.
This is caused by high mg/ml concentration gear. A combination of solvent PIP (above) and large amounts of the steroid being dissolved in solution of the carrier oil. When injected, exposure to biological conditions (pH, osmolarity, electrolytes,mechanical stress from muscle contraction and circulation etc.) can cause the gear to fall out of solution and crystallise within the muscle resulting in an inflammatory response. This is very similar to the condition gout and the formation of uric acid crystals. My advice is to be cautious when choosing high concentration products, yes you might be getting more mg/ml but is it worth the PIP? You might be able to reduce injection volume but then again having constant inflammation is also counter productive and can and will hinder your training, gains, and health.
Foreign Body/Particle PIP
This is from the presence of small particles such as plastic, dust, and also dead bacteria present in the gear. This is, in most cases, due to zero filtration being used in production and instead baking the gear in the oven at high temperatures which kills off any living bacteria present but does not remove them meaning they are still floating around but dead. Dust and other non-biological particles are not supposed to be in the body which is why when you inject this irritation and inflammation can occur. The dead bacteria on the other hand you might think is not that bad because it’s dead. It is actually still bad, think about your vaccines you get from the doctors for say TB, meningitis, or the flu shot. These vaccines are basically controlled doses of inactive dead forms of the bacteria responsible for that particular disease. So the flu shot contains inactive flu virus etc. How your body responds to these vaccines is through recognition of the surface of these pathogens through antigens, this then caused your immune system to produce antibodies against these antigens so that in the future when you are exposed to the real living disease your body can respond immediately and protect you. Now back to the bacteria present in the gear, the same thing happens and your body undergoes an immune response each time you inject causing inflammation and generally make you feel sick (fever, temperature, fatigue, etc). There is no control over how much bacteria or the different types of bacteria potentially present in the gear therefore the immune response can be quite severe. In most extreme causes the formation of an abscess can occur which normally resolves on its own but often requires medical intervention.
This is caused by poor technique and needle movement or the use of inappropriate needle gauge size which causes micro-injury of local muscle. Injection speed is also very important, pushing too hard can cause a jet stream effect which and further damage surrounding tissue, think of a pressure jet washer that pumps water at high speeds.
A combination of any of these can happen therefore it is important that we do our part and eliminate as many of these factors if possible by having good injection technique and using high quality gear that you can trust.