Oxidative is a natural process that happens to all living cells.
It takes place when oxygen(O2) interacts with cells. This happens everywhere, for example with fruit and vegetables. As soon as you cut them or peel them they start to go brown because of oxidation. Contact with oxygen produces changes in the cells. In the example of fruit cells start to die and rot once oxygen comes in contact. Whereas if we cut ourselves our cells are slowly replaced and covers the wound.
The birth and death of cells is a continuous process and our bodies are replacing old cells with new ones continuously throughout lives.
Our bodies are constantly producing free radicals through breathing, exercising and the food we eat. Free radical tend to injure our cells, damaging DNA and mutating them which leads to increased risk of health issues.
Think when a cell reproduces itself it becomes an imperfect copy of itself. Imperfect DNA copies can lead to various effects like ageing, degenerative diseases and cancers