Collagen is a protein that is naturally produced in the bodies of animals (especially mammals) and is the main component of connective tissues like cartilage (found in humans in places like the ears, the tip of the nose and between bones). It is also found in significant quantities within muscle tissue, where it contributes to the strength and elasticity of muscles.
TL;DR (Too Long; Didn't Read)
Collagen is a natural protein that is collected from the cartilage of dead animals or human remains which then go through a cooking process to separate it from other matter before the collagen can be used.
In order to be collected for use, collagen is taken from other dead mammals (usually livestock for commercial use). The basic extraction is generally done using a process of cooking cartilaginous animal materials, such as bones, connective tissues and skin. This process creates gelatin (a form of collagen that has experienced partial hydrolysis, combining with the water at a molecular level) and can often be witnessed in the home during the cooking of meat bones into soup. How the collagen gelatin is treated depends on what it is going to be used for, but it must at least be purified to remove other materials from the animal matter, such as fats and salts.
In some cases, collagen can also be collected from human remains (donated or leftover from surgical operations) when it is needed for medical use, since human-extracted collagen is less likely to be rejected by another human body.
Why It's Used
Though collagen is most popularly known by name for its use as a medical cosmetic item (for example collagen protein is injected under the skin to give a plumping and firming effect), the protein has many uses. Most commonly, collagen as gelatin is used as a food product, and is found in items such as gelatin desserts, gummy candy and some yogurts. Gelatin also has non-food applications. It is present in products like photographic film, gel capsules for pills and heat-soluable glues, such as those used in the making of stringed instruments.
In addition, collagen has a number of medical applications beyond its cosmetic use, such as the creation of artificial skin used to treat victims of severe burns.