A number of studies have demonstrated a strong association between the antioxidant properties of rosemary polyphenols and their chemoprotective activity. However, the prooxidant effects of rosemary polyphenols have been rarely reported. In this work, a foodomics study is performed to investigate the in vitro autooxidation of carnosic acid (CA), carnosol (CS) and a polyphenol-enriched rosemary extract (SC-RE) in cell culture conditions. The results revealed that rosemary polyphenols autooxidation in culture medium generated H2O2 at different rates. Generated H2O2 levels by SC-RE and CA, but not CS, were correlated with intracellular reactive oxygen species (ROS) generation in HT-29 cells, and were partially involved in their anti-proliferative effect in this cell line. These compounds also induced different effects on glutathione metabolism. Results also indicated that high extracellular H2O2 concentrations, resulting of using high (45 mu g/mL) SC-RE concentration in culture media, exerted some artifactual effects related with cell cycle, but they did not influence the expression of relevant molecular biomarkers of stress.