Eggshell powder is a finely ground form of chicken eggshells used primarily as a natural calcium supplement, but it also shows up in pet nutrition, gardening, skincare, and even water treatment. A single gram contains roughly 380 mg of elemental calcium, making it one of the most concentrated and affordable calcium sources available.
A Low-Cost Calcium Supplement
Eggshell is about 94% calcium carbonate, the same compound found in many over-the-counter calcium tablets. What sets it apart is the additional trace minerals. Analysis of eggshell powder shows it contains about 39% elemental calcium by weight, along with meaningful amounts of strontium, a mineral associated with bone strength. At the same time, levels of potentially harmful metals like lead, cadmium, and mercury are very low.
Half a teaspoon of finely ground eggshell powder provides around 1,000 mg of calcium, which is close to the full daily recommended intake for most adults. A single large eggshell, once cleaned and ground, yields about one level teaspoon of powder containing roughly 2,000 mg of calcium. That makes it a practical option for people in regions where dairy is scarce or supplements are expensive. Research from sub-Saharan Africa found that just one gram of eggshell powder covers about half a woman’s daily calcium needs.
Bone Health and Osteoporosis
The most studied use of eggshell powder is for bone support. Clinical studies in postmenopausal women and women with age-related osteoporosis found that regular eggshell powder intake reduced bone pain, slowed the breakdown of bone tissue, and either increased bone density or stopped further loss. Participants also reported improved mobility. These results are consistent with what you’d expect from any well-absorbed calcium source, but the natural presence of strontium and the small protein fraction (rich in the amino acids glycine and arginine) may offer additional benefit that refined calcium carbonate supplements lack.
Homemade Pet Diets
Eggshell powder is widely used by people who prepare homemade food for their dogs. Meat is high in phosphorus but low in calcium, and without a calcium source, a homemade diet creates a dangerous imbalance over time. Eggshell powder solves this neatly because it provides calcium without adding any phosphorus, making the ratio easier to manage.
General guidelines based on body weight give a sense of typical amounts:
- 7-pound dog: about 1/4 teaspoon per day
- 13-pound dog: 1/4 teaspoon (roughly 500 mg calcium)
- 30-pound dog: 1/2 teaspoon
Healthy adult dogs need a calcium-to-phosphorus ratio between 1:1 and 2:1. Dogs with kidney disease may benefit from a ratio up to 3:1. If you’re already feeding raw meaty bones as 25 to 30 percent of the diet, there’s no need to add eggshell powder on top of that, since bones are naturally rich in both calcium and phosphorus.
One important exception: puppies. Their higher phosphorus requirements mean eggshell powder alone isn’t sufficient. Puppies generally need a supplement that includes both calcium and phosphorus, like bone meal.
Eggshell Membrane for Joints and Skin
The thin membrane lining the inside of an eggshell is a different product from the shell powder itself, and it’s sold separately as a supplement. This membrane contains type I, V, and X collagen, along with several compounds that also exist naturally in human cartilage and skin: chondroitin sulfate, dermatan sulfate, hyaluronic acid, and keratan sulfate. It also contains elastin and the antibacterial protein lysozyme.
The overlap with joint and skin tissue is what drives interest. Clinical trials have shown that oral collagen peptides combined with chondroitin sulfate improved collagen fiber organization in human skin. Eggshell membrane supplements are marketed for both joint comfort and skin elasticity, though most of the stronger evidence comes from the individual components (collagen, hyaluronic acid) rather than the membrane as a whole.
The Garden Myth
Crushed eggshells are a popular gardening hack, especially for preventing blossom end rot in tomatoes, peppers, and zucchini. The logic sounds reasonable: blossom end rot is caused by calcium deficiency, and eggshells are packed with calcium. But according to the University of Minnesota Extension, this doesn’t actually work for two reasons. Most garden soils already contain plenty of calcium for plants. And even in soils that are truly calcium-deficient, eggshells decompose far too slowly to deliver that calcium when the plant needs it. The verdict from agricultural researchers is straightforward: eggshells do not prevent blossom end rot.
That said, finely ground eggshell powder does add calcium carbonate to soil over time, which can gradually raise pH in acidic soils. It’s just not a quick fix for any specific plant problem.
Water Treatment and Pollution Cleanup
Outside the kitchen and garden, eggshell powder is being used as a low-cost material for cleaning contaminated water. Its porous, calcium-rich surface is effective at adsorbing heavy metals like lead and zinc, as well as synthetic dyes like methylene blue. Researchers have found that chemically and thermally modified eggshell powder performs even better, pulling lead ions and dye molecules out of water at rates competitive with more expensive commercial filters. This makes it especially appealing for environmental cleanup in developing regions, where eggshells are abundant and industrial water treatment infrastructure is limited.
How to Prepare It Safely
Raw eggshells can carry Salmonella and E. coli, so proper sterilization matters if you’re making eggshell powder at home. Research has identified two reliable methods. Boiling eggshells in water at 95°C (just below a rolling boil) for 60 minutes eliminates Salmonella and brings bacterial counts to negligible levels. Steaming at 121°C for 15 minutes achieves the same result more quickly. After sterilization, dry the shells completely (an oven on low heat works), then grind them in a coffee grinder or blender until the powder is fine enough that you can’t feel any gritty texture between your fingers.
Particle size matters for absorption. Coarse fragments pass through the digestive system without breaking down fully. The finer the grind, the more surface area is exposed to stomach acid, and the more calcium your body can extract. Store the finished powder in an airtight container at room temperature.
Practical Limitations
Eggshell powder is calcium carbonate, which means it’s absorbed best when taken with food, since stomach acid production increases during meals. People who take acid-reducing medications may absorb less. It’s also worth noting that calcium carbonate can cause gas or bloating in some people, particularly at higher doses.
The trace mineral profile of eggshell powder depends on what the hens were fed and their environment. While studies consistently show low levels of lead and other toxic metals in eggshell powder, this applies to eggs from known sources with standard feed. Shells from hens raised in heavily polluted environments could theoretically accumulate more contaminants, though this hasn’t been documented as a widespread concern in the research to date.