skull and crossbones behind every warning label

The skull and crossbones symbol is an iconic image that has been used throughout history to represent danger, poison, and death.  Today, it is commonly associated with chemical hazard labels and warning signs.  However, the origins of this symbol are much older than most people realize, dating back to the days of the ancient alchemists and the bubonic plague.

Early Uses

One of the earliest known uses of the skull and crossbones symbol was by the ancient Greeks, who used it to mark tombs and graves. The symbol was later adopted by the Roman Empire and used as a symbol of death and danger.  During the Middle Ages, the skull and crossbones symbol was used in Christian art to represent the crucifixion of Jesus Christ, with the skull representing the location of the crucifixion (Golgotha).

During the Middle Ages, the bubonic plague ravaged Europe, killing millions of people. To warn others of the danger, plague doctors would wear long robes, gloves, and a mask with a beak-shaped nose filled with herbs and spices to protect themselves from the disease. These masks were often adorned with a skull and crossbones, which served as a warning to others to stay away – the symbol would also be marked on the doors of houses where people had been infected and on their burial sites.

The skull and crossbones symbol was also used by alchemists, who were the predecessors of modern chemists. They used the symbol to represent the element of sulfur, which was associated with the process of transmutation – they believed that they could transform base metals into gold, or other precious materials, and the symbol of the skull and crossbones represented the process of transformation or death and rebirth.  Many of their experiments were dangerous and potentially deadly so to warn people of the hazards of their work, alchemists would mark their experiments and laboratory equipment with the skull and crossbones.


It was during the Golden Age of Piracy in the 17th and 18th centuries that the skull and crossbones symbol became most closely associated with danger and warning.  Pirates would fly the Jolly Roger flag as they attacked merchant ships, sending a clear message that surrender was the only option.  The symbol was also used as a warning to other pirates, letting them know that the ship they were approaching was already under attack.  The title ‘Jolly Roger’ is thought to come from the French phrase ‘joli rouge’ which means ‘pretty red’ as the original pirate flags were blood-red, rather than black and white, and this signalled that no mercy would be given once the pirates boarded and battle ensued.

Chemical Labelling

Over time, the symbol became more broadly associated with poison and toxicity and was adopted by the medical profession as a warning for hazardous drugs.

The use of the skull and crossbones symbol for chemical labelling dates back to the early 20th century.  In 1914, the US government passed the Federal Hazardous Substances Act, which required that all hazardous substances be labelled with a warning symbol and so the skull and crossbones became synonymous with the classification and labelling of toxic and poisonous chemical substances.

Today, this symbol is still a ubiquitous sight in brightly lit laboratories and industrial settings all over the world – helping to protect the health of workers and the environment.  So, despite its dark and ominous history, the next time you see a skull and crossbones symbol on a chemical hazard label, remember its fascinating history and the important role it plays in keeping us safe.


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