Risks and side effects from collagen injections are rare, especially because Dr. Maercks will be performing an allergy test before treatment. However, it’s important to be aware of the possibilities, which include:  Having an allergic reaction  Itchy skin Infection Bleeding, bruising, or swelling at the injection site Bumps, clumping, or abscesses of the skin Uneven skin appearance Damage to tissue and nerves