Probably the most common side-effect is a ‘cortisone flare,’ a condition where the injected cortisone crystallizes and can cause a brief period of pain worse than before the shot. This usually lasts a day or two and is best treated by icing the injected area. Another common side-effect is whitening of the skin where the injection is given. This is only a concern in people with darker skin, and is not harmful, but patients should be aware of this. Other side-effects of cortisone injections, although rare, can be more serious. The most concerning is infection, especially if the injection is given into a joint. The best prevention is careful injection technique, with sterilization of the skin using iodine and/or alcohol. Also, patients with diabetes may have a transient increase in their blood sugar which they should watch for closely.
Studies on corticosteroids tend to lean toward the extreme use, rather than the average use. For example, some studies look at corticosteroids for extreme and rarer cases of eczema. This makes it harder to research what long-term studies are out there on steroid use. To complicate things further, corticosteroids can be oral, topical, injected, or inhaled, and this dramatically changes the benefits and risks, and in turn the short-term and long-term effects. Speak with your doctor and pharmacist on what, if any, long-term studies out there are relevant to your own medical treatment.