What is eggshell membrane, and what is it made of?

Eggshell membrane is the thin, papery film between an egg's hard shell and the egg white, the layer you see when you peel a boiled egg. It is made mostly of protein: a 2021 review puts it at about 80 to 85% protein, arranged as a net of fibres in three layers and held together by strong cross-links, which is why it does not dissolve in water. Collagen (types I, V and X) makes up about 10% of the membrane. Most of the rest is other proteins, including egg white proteins such as ovotransferrin and lysozyme and keratin, along with sugar chains called glycosaminoglycans. It is not a nutrient with a Thai Reference Daily Intake (Thai RDI).

In short:

• Where it is: between the shell and the egg white, in three layers
• What it is made of: about 80 to 85% protein, more than 500 different proteins
• Collagen: about 10% of the membrane, as types I, V and X
• Other parts: egg white proteins, keratin, glycosaminoglycans (sugar chains), a little calcium carbonate
• Processing: used whole (ground) or hydrolysed, meaning its proteins are broken into smaller pieces
• Egg allergy: it contains egg white proteins
• Thai RDI: none

This article explains what the membrane is, what it contains and how it is processed. For the difference between collagen peptides and gelatin, see Collagen peptides and gelatin: how do they differ?

What is eggshell membrane?

Where it sits in an egg

A 2021 review in the journal Foods, written by researchers from Nanjing Agricultural University in China and the Universities of Ottawa and Guelph in Canada, describes the eggshell as about 10% of the weight of an egg. The hard shell is about 95% calcium carbonate, with a small organic part of proteins and related molecules. The membrane is the innermost part of the eggshell, lying between the mineral layer of the shell and the egg white. Its fibres form a net that lets the shell build up its mineral on the outer side while the egg white stays free of mineral.

Three layers

The review divides the membrane into three layers, arranged in a spiral.

The fibres become thinner from the outermost layer to the limiting membrane. At the air cell, the small pocket of air inside the egg, the fibres of the inner and outer layers do not intertwine.

What is eggshell membrane made of?

Main components

Collagen in the membrane

Collagen is a family of proteins, and its types are numbered. The 2021 review says collagens are the main structural basis of the membrane's fibres and make up about 10% of the membrane. Types I and V occur at a ratio of about 100 to 1, and their amounts differ between layers: the inner layer contains both, the outer layer only type I. Type X is found in both layers. So although collagen is part of the membrane, most of its protein is something other than collagen.

Sugar chains (glycosaminoglycans)

Glycosaminoglycans are long chains of sugar units. A 2014 study led by Zhejiang Agriculture and Forestry University in China isolated them from each part of chicken eggs: yolk, thick and thin egg white, membrane and shell matrix. All four families were found in every part, but in different amounts. Chondroitin sulfates and hyaluronan were plentiful in the membrane and the shell matrix, while the yolk had only a trace of hyaluronan, and keratan sulfate was high in the egg white and shell matrix. These are comparisons between parts of the egg; the study does not give the amount in the membrane as a share of its weight.

Proteins found by Thai researchers

A 2013 study from Kasetsart University incubated fertilised eggs for up to 21 days and analysed the membrane's proteins at four points. It found 62 proteins. Keratin was the only one already known as a membrane protein, 8 were egg white proteins or related to them, and 53 had not been reported before. The types of protein differed with the time of incubation, so the study describes membranes from developing eggs rather than from eggs sold for eating.

Inner and outer layers compared

A 2003 study from the University of Alberta in Canada compared the inner and outer membranes with the organic part of the shell. Uronic acid was similar in the two membranes, sialic acid was higher in the inner membrane than in the outer one, and nitrogen was fairly constant between the two. The membranes had more proline and hydroxyproline, and less glycine and alanine, than the organic part of the shell.

Why does eggshell membrane not dissolve in water?

The membrane's proteins are tied together so tightly that ordinary methods struggle to separate them.

Cross-links between proteins

Researchers at the University of Delaware describe two disulfide-rich membranes made from fibres whose proteins are extensively coupled by irreversible cross-links derived from the amino acid lysine. They identified a cysteine-rich eggshell membrane protein (CREMP) built from long runs of repeating modules. The 2021 review lists CREMPs, keratins, desmosines and hydroxylysinonorleucine as the reasons the membrane is hard to dissolve in water.

Why this matters for processing

Because of these cross-links, the membrane has to be separated from the shell and then either used as it is, ground into a powder, or broken down chemically to make a soluble material. That leads to the difference between whole and hydrolysed eggshell membrane.

How is eggshell membrane separated and processed?

Separating it from the shell

The 2021 review says the membrane can be separated through mechanical, chemical or enzymatic treatment. The inner layer and the limiting membrane have to be separated by hand, while the outer layer is firmly attached to the shell and needs extra steps to remove. Because the shell is mostly calcium carbonate, dissolving it in acid releases the membrane; acetic acid, hydrochloric acid or EDTA are commonly used. Temperature, time, moisture and the type of acid all change how well the separation works.

Whole and hydrolysed membrane

"Hydrolysed" means the proteins have been broken into smaller pieces, such as peptides and free amino acids, by water, acid, alkali, enzymes or bacteria. Unhydrolysed membrane keeps its insoluble fibres. The review notes that the temperature used when making soluble membrane protein is controlled to avoid denaturing the collagens and other fibrous proteins (50 to 70 °C).

The figures come from different starting materials, units and methods, so they cannot be compared directly. In the 2025 study from Northwest A&F University in China, the amount of protein broken down changed with temperature, and collagen in the product changed structure as the temperature rose. In the 2017 study from the Asian Institute of Technology in Pathum Thani, the starting pH and fermentation time set how far the proteins were broken down. In the 2016 study from Tehran, the alkali strength, alkali time, enzyme amount and digestion time were varied to find the conditions that released the most pepsin-soluble collagen. The 2004 study from Tsinghua University used amino acid and elemental analysis to explain why its product dissolved.

Is there a recommended daily amount?

Eggshell membrane is not a nutrient with a Thai Reference Daily Intake (Thai RDI), so there is no recommended daily amount in Thailand. The figures in this article describe what the membrane contains and what different processes produce, not how much anyone needs.

Studies in this article are about the material

The studies here measured the membrane's structure, its components and the products of processing. They are laboratory analyses of the material, and they vary in the eggs used, such as fertilised eggs incubated for up to 21 days in the Kasetsart study.

Who should be careful with eggshell membrane?

People with an egg allergy

The membrane contains egg white proteins, such as ovotransferrin and lysozyme, according to the 2021 review, and the Kasetsart study also found egg white proteins among the membrane's proteins. The US Food and Drug Administration lists eggs among the nine major food allergens and explains that food allergies occur when the body reacts to certain proteins in food. People with an egg allergy should talk to a doctor or pharmacist before eating products made from eggshell membrane.

Safety studies

The 2021 review summarises laboratory and animal safety tests of eggshell membrane as a dietary ingredient. These are not studies in people, and they describe the material tested in them.

Pregnant or breastfeeding women and people who take regular medication

If you are pregnant or breastfeeding, or take medication regularly, check with a doctor or pharmacist before taking supplements.

Dietary supplements are not intended to prevent, treat or cure any disease.