 Abstract fungi and antifungal compounds are relevant to the United Nations Sustainable Development Goals. However, the modes of action of antifungals, whether they are naturally occurring substances or anthropogenic fungicides, are often unknown or are misallocated in terms of their mechanistic category. Here, we consider the most effective approaches to identifying whether antifungal substances are cellular stressors, toxins, toxicants, that are target site specific or have a hybrid mode of action as toxin stressors that induce cellular stress yet are target site specific. This newly described toxin stressor category includes some photosensitizers that target the cell membrane and, once activated by light or ultraviolet radiation, cause oxidative damage. We provide a glossary of terms and a diagrammatic representation of diverse types of stressors, toxic substances and toxin stressors, a classification that is pertinent to inhibitory substances not only for fungi but for all types of cellular life. A decision tree approach can. This article was authored by Delphine Noel, John E. Hallsworth, Eric Gelhay and others. We are article.tv, links in the description below.