Overall, dermal fillers are considered safe but the possibility of side effects cannot be completely ruled out, as with any medical procedure. Most of the side effects associated with dermal fillers are short-term side effects, occurring almost immediately after the injection and resolving in less than no time. Some permanent side effects have, however, been reported although rare.
If your physician wants to use collagen based fillers or fillers made from any other animal product, it is important you are first tested for allergies. Allergic reactions to these substances may be fatal and should be treated as an emergency. Common side effects that have been reported from the use of dermal fillers include bruising, swelling, slight itching or rash, pain, tenderness and an initial difficulty in undertaking otherwise simple tasks (common with hand fillers).
Nodules under the skin, necrosis, draining wounds and sores at the injection site are less common and more severe side effects that have been reported from the use of dermal fillers. Much severe side effects such as anaphylactic shocks, migration, rupture, formation of permanent nodules, blockage of blood vessels, stroke etc. have also been reported but these are extremely uncommon.