The object of the invention is to propose a novel biomarker for stress states, which biomarker is highly meaningful and capable of enabling quantitative measurements to be made of stress levels. To do this, it has been found, surprisingly, that the air at the end of a person's breathing out, known as "alveolar" air, contains fluorine compounds when that person has been subjected to various stress states. More precisely, the present invention provides components based on fluorine compounds, in particular fluorinated chloroalkanes, used as biomarkers of stress states.