Environmental stresses form reactive oxygen species in organisms and play a part in cell function, but higher doses in plants are lethal. Plants produce salicylic acid, a.k.a. aspirin, to protect chloroplasts.

Some studies have suggested e-cigarettes may be a healthier alternative to tobacco smoking, but a study lead by Prue Talbot shows epithelium gene expression does not revert to the same profile as non-smokers.