Collagen is a naturally occurring protein that exists in the skin and other connective tissue, but it breaks down as you age, resulting in skin that is increasingly wrinkled and saggy. As a temporary replacement for collagen in certain areas, some people opt for injections of liquid collagen, which can make skin firmer and smoother for up to six months 4. However, liquid collagen does have its risks and complications.

Skin Necrosis

According to "Secrets of Great Skin: The Definitive Guide to Anti-Aging Skin Care" by David J. Goldberg and Eva M. Herriott, Ph.D., a rare but potentially serious problem associated with liquid collagen injections is skin necrosis, the death of otherwise healthy skin cells 34. This happens when the collagen prevents the adequate flow of blood or oxygen to a group of skin cells. Once necrosis sets in, the affected skin cells cannot be saved, but without medical intervention, surrounding healthy tissue may become infected. The risk of this is small because collagen is typically injected in small amounts.

Unevenness

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Collagen beneath the surface of the skin can accumulate unevenly, resulting in skin that looks raised or bumpy, according to "The Smart Woman's Guide to Plastic Surgery: Essential Information From a Female Plastic Surgeon" by Jean M. Loftus 2. This is almost always a result of improper injection procedure, which is why it is important to seek this treatment from a qualified, experienced professional. When this happens, the lumps usually dissolve and even out over the course of a few days.

Allergic Reaction

The Mayo Clinic reports that approximately 3 percent of candidates are allergic to collagen injections 4. Allergies are primarily related to the most common form of liquid collagen, which is derived from cow or pig skin. Other sources of collagen include the patient's own skin, deceased collagen donors and collagen grown in a laboratory. To test for potential allergies, small amounts of collagen are usually applied externally to a patch of skin before it is injected. Allergic reactions usually manifest as redness, bumps and rashes, but can include skin ulcers. Allergic reactions to collagen that is actually injected may be more severe.

Infection

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As with any type of injection, there is a chance of infection, though this chance is minimal if the collagen injection is administered by a professional in a sterile setting. Infections can occur if bacteria is allowed into the injection site or if it is present on the needle used. Infections are typically treated with antibiotics.