New research suggests that your visits to such places can be tracked by analyzing chemical traces in your hair. (sciencemag.org)
The spike in CO2 and other chemical traces recorded would be just one big clue, but not the only. (judithcurry.com)
[25] Even organic produce contains chemical traces; you can wash some of it off, but research shows that washing does not remove all the chemicals. (globalhealingcenter.com)