Collagen is a protein needed for bone and skin health. Possible side effects of collagen include stomach upset, allergic reactions, and a rare skin reaction.

You’ve had collagen in your body since the day you were born. But once you reach a certain age, your body stops producing it entirely. This is when collagen injections or fillers can come into play.

Many people sing the praises of collagen, saying it can improve the health of your skin, hair, nails, and bones. Still, it’s a good idea to look into possible collagen supplement side effects and ...