The relations between forests and health carry ambivalent representations anchored in a long history. The dangers of deforestation and the usefulness of woodland to counter the "miasmas" and later the "pollution" are consistent with a Hippocratic approach that was reinterpreted at the end of the 18th century in the light of new knowledge in chemistry and biology. As of the 1970's, biodiversity was taken into consideration for the purposes of protecting and preserving forests seen as indispensable factors for public health. Conversely, the threats coming from tropical forests, that had been recognized for at least three centuries, and forest zoonoses that have been better identified all over the world in recent decades, are the negative side of this health-oriented representation of the role of forests. The analysis conducted in this article focuses on showing how these seemingly opposite views are actually complementary: once the mechanisms behind the diseases are better understood, the conservation of forests and their renewal become major goals for the populations concerned and for public authorities on the local, national and international scales, acting through numerous scientific studies and the establishment of public and private organisations. In this area, the role played by France is still too limited. A scrutiny of the last three centuries provides a better understanding of the essential character of social demands, cultural representations and medical expertise in the implementation of forest therapy and health-oriented environmental policies.