From James D. Wilson
Lovers of forest air might reflect that it may not be entirely health-giving (6 August, p 44). It is replete with terpenes. Certain terpenes, notably the d-limonene responsible for the odour of lemon, cause cancer when fed to animals. This particular response is species-specific and not predictive of cancer in humans, so there is no need to eschew lemons and oranges.
Yet very few terpenes have been tested. Experience suggests that roughly half will come up positive in the standard tests. Either the tests are poor predictors of carcinogenicity in humans, or forest air is no more healthful than ordinary air.
I would like to think that the former is true, and will continue to enjoy the cool of the woods.
St Louis, Missouri, US
