What are collagen injections side effects?

It really depends on which collagen you get. Currently there are three commercially available forms:

Bovine (cow)
Porcine ( pig)
Cadaveric (human)

Reactions differ most notably in the ability to cause an allergic reaction with decreasing severity in the order listed above. Bovine typically requires a skin test 1 month before treatment and therefore is rarely used any longer.
Most commonly people complain about the relatively short lived results but other issues are the potential lumpiness of the product. In some situations, however, it remains an excellent product for fine lines.

Collagen injections have fallen into disfavor. Bovine (cow) collagen and human collagen are hardly used any more. Skin allergies manifested as red bumps did occur in 1 - 3 % of people with bovine collagen. Porcine (pig) collagen, manufactured as Evolence, will no longer be distributed by J and J. Injectables are mostly the hyaluronic acids such as Restylane and Juvederm, Hydrelle (hyaluronic acid premixed with anesthetic) and Radiesse.
Bruising, tenderness, lumpiness, uneveness, bluish color of the skin over a lump (unique to the hyaluronic acids) and rare vascular compression complications including scarring can occur. There are other rare risks that your doctor can discuss with you.

There are several different kinds of collagen injection fillers. The oldest collagen and the original filler was made of cow collagen and about 3% of people were allergic to it. Today, the newest collagen is called Evolence. It is derived from pig collagen and is a wonderful filler. Allergies to this are very rare. However, Evolence is manufactured by Johnson & Johnson, and they have decided not to continue distribution of this product. We believe this same product will eventually be marketed by another company.

WHY would you be getting Collagen injections when there are so much better and longer lasting fillers out there?
The label COLLAGEN refers to the original products Zyderm/Zyplast (now owned by Allergan producer of Botox, Latisse and Juvederm) which were isolated from COW COLLAGEN. They could not be used in people allergic to beef products and required at least one skin test 3-4 weeks before use. (Some used 2 skin tests because up to 4% of those who did not react to the first skin test were allergic to beef products and would react to a second test). The products were NOT cheap, were short lasting.
As far as adverse effects aside from the allergy issues, the FDA prohibited the filling of lips with Collagen ("Paris Lips") but otherwise the products had a good safety record if not an impressive durability record.
With so much better products out there, a lot of us still have unused Collagen in our refrigerators. Could you ask your ?doctor if he/she would take my Collagen off my hands? I'm ready to deal....
Peter A Aldea, MD

Collagen is a dermal (skin) filler used for minimizing wrinkles or some depressed scars.  The collagen products that were widely used (Zyderm, Zyplast, CosmoDerm, CosmoPlast) were taken off the market in 2010 since Allergan, the manufacturer/distributor, also sells the Juvederm family of injectable fillers, and these fillers last longer than collagen. The Juvederm family is made of hyaluronic acid (natural substances found in our bodies, but synthetically derived from bacteria) and have become more popular than the collagen products, not only because they last longer (6 to 12 months), but they can also be injected into deeper levels, thereby acting as "volumizers". Just as a clarification, Restylane/Perlane, are also hyaluronic acid derivatives, and plastic surgeons may have a preference of one brand over the other.

All injectables may have local tissue reactions, such as needle stick marks, pain during injection, tenderness after injection, redness, bruising and swelling.  When injecting collagen products, these side effects generally last no more than 1 hour.  HA's have more local tissue reaction, so those side effects will last longer:  My personal experience is that the Juvederm family reactions last about 4 hours, Restylane/Perlane may last for about 24 hours.  The deeper fillers (Juvederm Ultra Plus and Perlane) are more likely to have persistent swelling and possibly bruising for several days. As an aside, collagen, if derived from bovine (cow), has the potential risk of allergic reaction.

There are some longer lasting products, including ArteFill, which contains bovine collagen mixed with a bone-like derivative, synthetic polymethylmethacrylate (PMMA).  It lasts for 3 to 5 years, but a significant risk is "foreign body reaction", or lumpiness at the injection site.  It is very technique dependent and although steroid injection into the lumps may help to minimize their appearance, the usual treatment is excision (cutting them out). This is a significant side effect that warrants consideration when choosing a filler! 

Finally, there has been recent attention to unusual side effects of injectable fillers.  They include unusually severe infections and embolic reactions (particle of filler enters a blood vessel and travels distally, causing a blockage of the vessel, resulting in death of the tissue the vessel supplies).  My personal belief is that we are seeing more of these problems because 1) the availability of deeper fillers and 2) many "providers" with less than adequate training and experience are administering these fillers.

There are presently three collagen products on the market, but that probably will change.
Zyderm and Zyplast are the grand daddies of all the fillers, being introduced in 1981 and 1985 respectively. They are derived from bovine collagen and require allergy testing---the only filler for which this is necessary. It is fairly short lived (3-4 months) and is a bit "stiff". It is not used very much anymore, most physician fillers believe its day has passed. but occasionally some of the people who liked it originally don't want to try anything else and will ask for it.
The second collagen filler to hit the market was Cosmoderm/Cosmoplast. This is human derived, obviating the need for allergy testing. It is also short-lived, not lasting much longer than Zyderm/Zyplast. It is somewhat more malleable than its predecessor. It is most useful today for some of the finer lines, say smoker's lines and crow's feet. Many physicians like it to line the vermilion border.
Finally, there is Evolence. Johnson & Johnson, the manufacturer, recently announced they were no longer going to market or manufacture it. Most likely, the rights will be sold to another company. Evolence is derived from porcine (pig) sources. The part of the molecule which is porcine is cut off so one does not need allergy testing. Evolence is for slightly deeper lines. My feeling is that it gives a somewhat more natural correction (after all it is collagen that gives the most substance to the dermis) than the hyaluronic acid fillers.
As far as side effects. The collagen fillers can cause redness, and swelling. This would be accentuated if you exercise, sweat or lay in the sun. This would be the most common side effect.
You should also be very careful if there is a personal or family history of collagen vascular disease. There was quite a controversy in the 1990's when trial lawyers claimed there was an increase in polymyositis/dermatomyositis. In fact, the FDA reviewed the data again, coming to the conclusion that collagen ( then only Zycerm/Zyplast was available) was safe.
One problem with collagen fillers is that they can leave small bumps in the skin if the injection is delivered too close to the surface This really is not much different than the bluish bump of the hyaluronic acid fillers, except it is a bit less noticeable with collagen. Unfortunately, this complication is less amenable to treatment than the HA fillers. There is nothing equivalent to hyaluronidase, to erase any mistake.
The complication we most fear with fillers...and this can happen with the HA fillers too, is tissue necrosis. Tissue necrosis means the death of sometimes large areas of tissue. Gangrene is not good and this occurrence will require a large amount of plastic surgery to make good again. Tissue necrosis can occur when either the filler encroaches on a blood vessel or the material itself enters a blood vessel. There are two areas of the face which are especially dangerous, the glabellar region (between the brows) and that at the upper naso-labial fold (smile lines). This problem was more common with the bovine collagen fillers. I personally did not know of a case with this filler, but know of three cases of this with HA fillers (all three times by nurse injectors by the way--not that this cannot happen with physicians).