The potential occurrence of synergistic effects presents a special case, and may occur for example when one substance increases the toxicity of another, e.g. if substance A inhibits the detoxification of substance B. Currently, predictive approaches cannot account for this phenomenon. Gaps in our knowledge of the modes of action of substances as well as circumstances under which such effects may occur (e.g. mixture composition, exposure concentrations, species and endpoints) often hamper predictive approaches. Indications that synergistic effects might occur in a product will warrant either a more precautionary approach, or product testing.chemical