The most common side effect is known as a cortisone flare. This is thought to happen when the steroid crystallizes after being injected. In patients who experience a flare, a brief episode of pain lasting one or two days follows the injection. This pain can be worse than the initial discomfort for which the injection was given. Cortisone flares resolve spontaneously over a few days and can be treated with ice and immobilization.
Another common side effect, especially in patients with darker skin, involves skin discoloration at the injection site. The skin becomes locally lighter in color and sometimes thinner. Although this can improve, the whitening of the skin can sometimes be permanent.
One of the more serious complications from steroid injections is an infection, especially if the injection was given into a joint. Fortunately, infections are rare and can usually be prevented by carefully cleaning the skin before performing the injection. Very rarely, some patients may experience allergic reactions to the steroid or local anesthetic in the injection.