It is easy enough to recognise a smoker or someone who chews tobacco... it shows primarily in the stains on their teeth. Keeping this in mind, a research team extracted nicotine from ancient dental plaque in the hopes of understanding the history of tobacco consumption.

For the first time, scientists were able to extract the nicotine residue from plaque of teeth belonging to eight individuals who were buried between 6,000 and 300 years ago.

By using this new method, they hope to identify the kinds of people who consumed tobacco centuries ago.

"The ability to identify nicotine and other plant-based drugs in ancient dental plaque could help us answer longstanding questions about the consumption of intoxicants by ancient humans," Shannon Tushingham, a Washington State University assistant professor of anthropology said. "For example, it could help us determine whether all members of society used tobacco, or only adults, or only males or females."

The findings have been published in the Journal of Archaeological Science Reports.

Tushingham, along with David Gang, a professor in the WSU Institute of Biological Chemistry, Korey Brownstein, a graduate student in the WSU Molecular Plant Sciences Program, and Jelmer Eerkens, an anthropologist at the University of California, Davis, collaborated with members from the Ohlone tribe in San Francisco Bay to get access to the ancient remains.

The WSU researchers used liquid chromatography-mass spectrometry to test the samples for nicotine and other plant-based drugs like caffeine and atropine, a muscle-relaxant. Two samples tested positive for nicotine, a man who had been buried with a pipe and an older woman.

"While we can't make any broad conclusions with this single case, her age, sex, and use of tobacco is intriguing," Eerkens said. "She was probably past child-bearing age, and likely a grandmother. This supports recent research suggesting that younger adult women in traditional societies avoid plant toxins like nicotine to protect infants from harmful biochemicals, but that older women can consume these intoxicants as needed or desired."

The search for traces of other intoxicating substances was not detected in any of the samples but the team is hopeful that further testing will reveal the desired results.

"We think a wide variety of plant-based, intoxicating chemicals could be detected in ancient dental plaque," Brownstein said. "It really opens up a lot of interesting avenues of discovery."

Up until now, tracing ancient spread of tobacco in the Americas has relied on studying pipes, charred tobacco seeds and analysing hair and faecal matter. However, studying teeth could provide more information given the larger archaeological supply available. In the case of teeth, dental plaque adheres to the surfaces and mineralizes over time, preserving a wide range of substances that are in the mouth.

Understanding what particular individuals consumed would only require testing this material.