There are several types of risk involved in fillers. One is that if you go to someone who is untrained and he puts the filler in the wrong location, you could have swelling or asymmetry or bruising or in rare cases even bleeding. If you go to a board-certified dermatologist who is trained in fillers that almost certainly not going to happen. The most common side effects of fillers are variable swelling for a few days. Certainly when you inject fillers into the lips or the lines under the eye socket you can have swelling for a day or two. Bruising is perhaps the most common side effect of fillers. There is really no significant risk of allergic reaction and the infection risk is virtually nonexistent.