Free radicals are unstable molecules with unpaired electrons.
The body metabolises oxygen efficiently but its believed that 1 / 2% gets damaged in the process and these molecules turn to free radicals.
They are free as they are missing a critical electron which sends them off desperately in search of the missing electron.
During this hunt for the missing electron, they don’t just kill cells but injure them which damages the DNA.
Once this DNA has been damaged it becomes mutated. A mutant cell can grow and reproduce rapidly and abnormally.
When these damaged DNA cells reproduce themselves they are an imperfect copy of themselves which can lead to chronic health problems.
Once the free radical steals an electron from neighbouring molecules these cells themselves become free radicals as the electron is missing it can not function.
Damage to the molecule, therefore damage to the cell and DNA so malfunctioning.
We constantly produce free radicals through breathing, exercising and food but our body can cope with this.