# Reactive oxygen species (ROS)

Reactive oxygen species (ROS) are unstable molecules that contain oxygen. The main ones are superoxide, hydrogen peroxide, and hydroxyl radicals. Your cells make them in several places. The big sources are mitochondrial energy production, enzymes called NADPH oxidases, peroxisomes, and the burst immune cells use to kill germs. In small amounts, ROS are useful. They act as signals that help run your immune system and metabolism. In excess, they are harmful. They damage your fats, proteins, and DNA. Over time, that build-up feeds mitochondrial decline, cellular senescence, and age-related diseases of the heart and brain.

## Sources

- Ames BN, Shigenaga MK, Hagen TM. (1993). Oxidants, antioxidants, and the degenerative diseases of aging. Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.90.17.7915
- Sena LA, Chandel NS. (2012). Physiological roles of mitochondrial reactive oxygen species. Molecular Cell. https://doi.org/10.1016/j.molcel.2012.09.025

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