Dispelling Some Myths: Romans brushed their teeth with Urine

While teaching primary school children about the Romans, and specifically hygiene, we have encountered the belief that they cleaned their teeth with urine. We mention this only because on May 9th, 2022, a link to an article by ancient-origins.net on this very fact was highlighted on Twitter by Roman historian and author, Dr. Mike Bishop (@perlineamvalli). In the linked article, ‘Ancient Romans Brushed Their Teeth with Urine’, Bryan Hill states: ‘The Romans believed that urine - both human and animal - would make their teeth whiter and keep them from decaying, so they used it as a mouthwash and mixed it with pummis to make toothpaste. In fact, urine was so effective that it was used in toothpastes and mouthwashes up until the 1700s’ (Hill, 2022). Dr Bishop, however, challenges the misleading implications writing that ‘not all Romans [followed this practice] as a matter of course’ and that the poet ‘Catullus (Poem 39) actually mocks someone for doing it’. Dr Bishop also notes Catullus’ implication that it was ‘a Celtiberian, not a Roman, trait.’ In other words, cleaning ones teeth with a urine-based mouthwash or paste was an un-Roman act, and any Roman doing so should be publicly ridiculed.

So, did the Romans brush their teeth with urine? Probably not. Be honest - would you? Yet why does this ‘factoid’ have such a hold on popular imagination? We suspect it is simply a case that it appeals to our notions of disgust.

Urine’s cleaning properties  Yet, in ancient times urine was a valuable commodity. It contains a wide array of important minerals and chemicals such as phosphorus and potassium. Urine was a rich source of urea, a nitrogen-based organic compound. When stored for long periods of time, the urea in stale urine decays to produce ammonia, a chemical used in many household cleaners today. Ammonia is highly effective at neutralising any acidity in dirt and grease, and is therefore very useful in breaking down fat molecules and removing stains from clothing. In ancient Rome, vessels for collecting urine were commonplace on streets. Passers-by would be encouraged to relieve themselves into them and when full the contents were taken to a fullonica (a laundry). The stale urine would be diluted with water in a large vat into which dirty clothes would be added. A laundry worker would then stand in the tub of urine and agitate the clothes with their feet in a similar way that a modern washing machine works (Kumar, 2013).

Vectigal urinae  In the 1st-century AD, Emperor Nero levied the vectigal urinae meaning ‘urine tax’ on the buyers of urine collected from public urinals. After Nero’s death in AD 68 the Roman world was plunged into a civil war known to us as ‘the year of the four Emperors’. Imperial power was eventually seized by Titus Flavius Vespasianus who became emperor in AD 69 and ruled for the next ten years until his death in AD 79. On his succession Vespasian began levying a series of taxes aimed at raising funds to restore the treasury’s finances and deliver the Empire from debt. One measure, re-introduced around AD 70, was charging for the collection of urine from the public urinals feeding Rome's Cloaca Maxima, its great sewer system.

Pecunia non olet  Known for his love of money and hardnosed taxation, Vespasian is also credited with introducing the first public toilets, nicknamed locally as ‘Vespasians’, in AD 74. However, his eldest son and future emperor, Titus, thought the urine tax a disgusting policy and complained to his father about it. According to the Roman historians Dio Cassius and Suetonius, Vespasian reputedly replied by picking up a gold coin and remarking ‘Pecunia non olet’ (‘money does not stink’) meaning that money is not tainted regardless of its origins.

A colourful past  Urine not only got clothes cleaner, but made colours brighter. Today cloth is coloured using chemical dyes but in the past natural dyes from seeds, leaves, flowers, lichens, roots, bark, and berries were used. These colours can leach out of cloth if it or the dyebath are not treated with mordant to bind the dye to the cloth’s fibres. The process works by wrapping dye molecules called chromophores inside a more complex molecule or a group of molecules to form a shell around the chromophores. The molecules forming this shell ensure the dye’s colour remains visible while enabling the dye to bind to the cloth and protecting it from bleeding away. Textile manufacturers quickly discovered that stale urine, or more precisely the ammonia in it, is a good mordant (Kumar, 2013).

Urine’s ammonia content was also important in the textile industry for bleaching wool or linen, and in tanning leather to soften it. Diluted in water ammonia acts as a caustic but weak base. Its high pH breaks down organic material making urine the perfect substance to soften and prepare animal hides for tanning. Soaking animal skins in urine also made it easier for leather workers to remove unwanted hair (‘unhairing’) and bits of flesh (‘fleshing’) from the hide.

References:

Hill, B., (2022), ‘Ancient Romans Brushed Their Teeth with Urine’, Ancient Origins, available online (accessed May 12th, 2022).

Kumar, M., (2013), ‘From Gunpowder to Teeth Whitener: The Science Behind Historic Uses of Urine’, Smithsonian Magazine, available online (accessed May 12th, 2022).