“Pee-cycling”: How human urine can strengthen teeth and bones

Did you know that ancient Romans gargled urine in order to get whiter teeth?¹ While people don’t gargle urine anymore, thank goodness, it may soon appear in people’s mouths again.

How? Through “pee-cycling.”

Ecologically minded scientists are working on a new use for human urine: transforming it into hydroxyapatite, a calcium phosphate mineral projected to hold a market value of more than $3.5 billion by 2030, according to UC Irvine News.²

Urine recycling could revolutionize tooth enamel repair

The human waste could soon be contributing to stronger tooth enamel and bones for implants, thanks to the team of 11 scientists from California, Illinois, and Japan. Removing urine from wastewater is also an environmentally friendly move, as it helps decrease pollution and the buildup of unwanted nutrients in the water.

Scientists have known for a while that nutrients such as nitrogen and phosphorus can be recovered from urine. But the low economic value of these products limited large-scale adoption, according to the study published in Nature Communications.³

So the scientists turned their sights to bigger ideas—genetically modifying yeast to take the elements present in urine to create hydroxyapatite, calling it “osteoyeast.” This process will reduce the cost of hydroxyapatite production and make the bone regenerating material more accessible for a variety of reasons, including for use by dental professionals.

Teeth are far from the only beneficiaries the scientists envision from their pee-cycling. Other uses may include archaeological restoration, biodegradable alternatives to plastic, and building materials for construction projects.⁴

Pee-cycling hydroxyapatite: A sustainable solution for dentistry and beyond

One of the coauthors, David Kisailus, UC Irvine professor of materials science and engineering, said, “This process to yield hydroxyapatite, or bone mineral, takes less than one day. The fact that it uses yeast as a chassis, which is inexpensive and can be placed in large vats at relatively low temperatures … shows that this can be done easily without major infrastructural needs, and that has the added benefit of making it accessible to developing economies.”

While we wait the next few years to see this new form of hydroxyapatite become reality, we may not be able to think about our urine the same again.

Read the study, Cost-effective urine recycling enabled by a synthetic osteoyeast platform for production of hydroxyapatite.

Download the e-book, All about hydroxyapatite with Anne O. Rice

References

1. Kumar M. From gunpowder to teeth whitener: the science behind historic uses for urine. Smithsonian magazine. August 20, 2013. https://www.smithsonianmag.com/science-nature/from-gunpowder-to-teeth-whitener-the-science-behind-historic-uses-of-urine-442390/

2. Researchers create method for converting urine into high value bio implant material. IC Irvine News. June 17, 2025. https://news.uci.edu/2025/06/17/researchers-create-method-for-converting-urine-into-high-value-bio-implant-material/

3. Muller IE, Lin AYW, Otani Y, et al. Cost-effective urine recycling enabled by a synthetic osteoyeast platform for production of hydroxyapatite. Nature. May 6, 2025. https://www.nature.com/articles/s41467-025-59416-8

4. Turner B. Scientists transform pee into material fit for medical implants. Live Science. July 4, 2025. https://www.livescience.com/health/scientists-transform-pee-into-material-fit-for-medical-implants