Eggshell membrane is the thin, almost transparent layer that sits between an egg's hard shell and its white. If you have ever peeled a boiled egg, you will have seen it. It is a natural fibrous tissue made largely of protein, and it contains several of the same building blocks found in joint cartilage.
Analyses show it naturally contains collagen, hyaluronic acid, chondroitin sulphate and glucosamine-related compounds, together with other proteins such as elastin. The amounts of each are small and vary with processing, so it is best thought of as a whole-food ingredient rather than a concentrated source of any one compound. Supplement makers separate the membrane from shells left over by the egg industry, then dry and mill it.
On labels you may see it as eggshell membrane, natural eggshell membrane or NEM. It is usually sold in small capsules, often in joint formulas. Researchers have studied it in small randomised trials looking at joint comfort and stiffness, with encouraging results, but the studies have been short and relatively small.