Ancient Romans Used Urine as Mouthwash

While the Romans are famous for their aqueducts and bathhouses, their approach to personal hygiene involved some startlingly different ingredients than we use today. The secret to a bright Roman smile wasn't a paste but a rinse derived from human urine. The key ingredient was ammonia, which forms as urea in stale urine decomposes. This powerful cleaning agent acted as a natural bleach (Review), effectively lifting stains and whitening teeth. This wasn't just a folk remedy; it was a widespread practice, with vats left in public spaces for citizens to contribute.

The use of urine as a cleaning agent was a cornerstone of Roman industry, also employed for laundering togas and tanning leather. The trade in this unusual commodity became so significant that specific types were prized above others. Urine from Portugal was considered particularly potent and was imported at a high cost, creating a lucrative cross-empire business. The practice was so established and profitable that Emperor Nero instituted a "vectigal urinae," or urine tax, to capitalize on its collection and sale. This strange historical fact is a testament to Roman resourcefulness and their practical, if not always pleasant, application of chemistry.