Fillers are products that are injected to restore or replace volume. There are many different types of fillers available including collagen, hyaluronic acid, polylactic acid, and calcium hydroxylapatite. The most commonly used fillers are hyaluronic acid fillers. Collagen injections are less popular now as they often produce allergic skin reactions.
For more information about fillers visit http://www.believeclinics.com/treatments/injectable-fillers.html