Since its FDA approval in late 2003, Restylane has been touted as the safer alternative to other similar facial fillers - many of which are made with rooster combs. Because Restylane is a non-animal hyaluronic acid filler, it does not come with the risk of animal-borne infections that exist in fillers made with animal products.

Still, there have been a few side effects associated with Restylane injections. Allergies are less common with Restylane than with animal products, but can still occur in rare cases.

The most common side effect is bruising, which is seen in roughly 20 percent of all patients. People also experience more pain with Restylane injections than they would with collagen injections because collagen has an anesthetic.

Some patients may also experience swelling at the site of the injection; this usually subsides within a few days. In other cases, people acquire an infection or cold sore at the point of the shot.

Pain, redness, itching, discoloration and tenderness at the point of injection are also common side effects that occur after a Restylane treatment. These effects usually subside within a day or two.

Most side effects experienced by Restylane patients are classified as mild. However, roughly one in 2,000 patients suffers more severe reactions, such as extreme tenderness, long-lasting redness and acne-like skin formations. These side effects can last for only a few days after injection up to as long as four weeks after treatment. Hypersensitive skin is usually to blame for more serious reactions to Restylane.