Curious uses of urine through the ages

A color fixer

Who doesn’t like to wear colorful clothes? If you were living in ancient or medieval times, however, the colors on your clothes would fade fast. The dyes used at that time were prepared from natural sources such as plant parts, insect bodies, and minerals, and they tended to run when the fabric was washed.

To prevent this leaching, stale urine was used as a mordant—a chemical that binds to the dye and the cloth, acting as a molecular bridge between the two while protecting the color from breaking down from exposure to light, water, and rinsing. At the molecular level, the ammonia formed from the decomposition of urea in the urine acts as the mordant. Urine was also used to chemically transform the natural dye indigo into a water-soluble form so that it could physically bind to fabric. The liquid waste was sourced from domestic chamber pots as well as collection vessels left in public places, and by the 16th century, it was even transported cross-country in England to meet the heavy demands of dyers.

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A textile cleaner

Although not the detergent of choice in the 21st century, urine was used to clean clothes in ancient Rome. The ammonia in stale urine is a bleach, which made it an ideal cleaning and whitening agent when mixed with water. Roman fullers, or launderers, soaked dirty clothes in the urine collected from public toilets and stomped on them until the stains were removed. Urine, called “chamber lye” or “lant” in England, was used as a cleaning agent for clothes until the mid-19th century. Its use was gradually discontinued as aniline dyes and mass-produced ammonia-based cleaners entered the market.

The importance of urine as a cleaning and bleaching agent is evident from one fact: Roman fullers had to pay a urine tax to use it.

A teeth whitener

Some experts dispute the historical accuracy of this claim, but literature suggests that some ancient Romans, Celtiberians, and Gauls may have mixed human or animal urine into their dental concoctions to get their pearly whites. The same stain-removing potency that made urine a prized cleanser and bleach for textiles in antiquity is thought to have inspired its use in dental care. But the historical medical use of urine was not limited to mouthwash. From ancient Rome to early modern England, it was recommended for treating a wild spectrum of afflictions—from simple sores to the bubonic plague. Similarly, India’s Ayurvedic medicine system has long extolled the benefits of consuming cow’s and one’s own urine. Such beliefs continue in the 21st century, with certain factions making unproven claims about urine’s purported antiviral actions against the COVID-19–causing coronavirus.

Although Western medicine has long since abandoned urine in its crude form, its key component, urea, remains a staple in modern dermatological treatments.

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A gas mask

Although it was not engineered into an actual gas mask, urine offered some functional protection against a deadly poison gas during World War I. In 1915 Allied forces fighting German armies in Ypres, Belgium, were confronted with a novel weapon: poisonous chlorine gas released from pressurized cylinders that German soldiers had buried in the ground. The gas was highly toxic to the respiratory system, causing asphyxiation, convulsions, and, in severe cases, death. Caught unprepared for chemical warfare and lacking standard-issue gas masks, Allied soldiers improvised by covering their mouths and noses with handkerchiefs or pieces of cloth drenched in water or urine. Although both helped mitigate the effects of the gas, urine offered some degree of chemical protection because its ammonia partially neutralized the chlorine, reducing the gas’s damaging and potentially lethal effects on the lungs. As the war raged on, this makeshift countermeasure was replaced by more sanitary and effective innovations, including gauze pads soaked in hyposulfite solution, flannel hoods, tube helmets, and box respirators.

About 1.3 million soldiers are estimated to have been killed or injured as a direct and immediate consequence of gas attacks during World War I. The unprecedented scale and widespread use of chemical weapons led historians to refer to the conflict as “the Chemists’ War.”

A cooking medium

To be precise, urine serves as a boiling medium for a delicacy in the city of Dongyang, located in China’s Zhejiang province. However, not just any urine will do. According to tradition, the urine must be collected from prepubescent boys, typically under the age of 10, to be effective. The supposed benefit? Local tradition holds that eggs soaked and boiled in the urine of young boys protect the body against heat stroke and joint pain. It is also thought to boost energy and improve blood circulation. Although the health benefits of these tongzi dan (“virgin boy eggs”) remain elusive to modern medicine, consuming them is a centuries-old springtime tradition in Dongyang, so much so that the local government has officially recognized it as an intangible cultural heritage.

A cottage industry has flourished around the sale of these eggs. Vendors gather their primary ingredient from local elementary schools, where young boys relieve themselves in buckets. The process of cooking the eggs takes almost a day. The eggs are first soaked in urine, then boiled in it until their shells harden. The eggs are then shelled and cooked on low heat, with fresh urine and herbs added as required. Egg whites turn pale golden and the yolks take on a green color because of the unique cooking process.

How do these eggs taste? According to connoisseurs, they possess a fresh, salty flavor—albeit with a hint of urine.

A creative tool

Human urine tends to be slightly acidic. It can react with metals such as copper, causing oxidation. This is the principle behind artist Andy Warhol’s 1977–78 series, Oxidation. For these works, Warhol covered canvases in a metallic gold and copper background and had friends and acquaintances urinate directly onto them. The uric acid in the urine corroded the copper in the paint, breaking down the pure metal into mineral salts. Some colors emerged instantly, but others, such as blues and greens, developed later over the initial red or brown copper oxides. The reaction was highly unpredictable and was influenced by variations in humidity, acidity, and individuals’ food and water intake. As a result, no two pieces turned out to be exactly the same.

A brief HVAC failure at the Andy Warhol Museum in Pittsburgh in 2020 triggered temperature and humidity spikes that caused a large Oxidation canvas to drip and melt. A similar incident had occurred during an exhibition in Paris while Warhol was alive. These incidents highlighted the chemically unstable and evolving nature of the Oxidation paintings. To understand how to preserve them, conservators examined archives, audiotapes, and historical records to identify the exact materials Warhol used in the 1970s. They also created replica canvases coated with matching vintage metallic paint, so that they could study the paintings’ chemistry without risking the originals. Volunteers then partially recreated Warhol’s studio protocol by applying urine to the mockups with pipettes. They even took vitamin B supplements before donating their urine. Why vitamin B? Warhol preferred to use urine from an associate taking the supplement to give his paintings “a really pretty color.”