An example is when asbestos particles are in the lungs. The chemicals the macrophage uses to destroy invaders end up getting secreted continuously. These chemicals, peroxides and free radicals, can serve as promoters in the tissue because they cause mutations and damage membranes and proteins in the cell too. A molecule with an unpaired electron. This makes it very reactive.
Water is an example of a molecule where all the electrons are paired.
The OH free radical has a single unpaired electron. Peroxides frequently react to form free radicals. A. Testing chemicals to see if they're bad. Test developed by Bruce Ames. If a chemical mutates DNA in bacteria, it can cause cancer.