These two terms are thrown around a lot in the media. Free radicals are bad, and antioxidant stop them, somehow. Explanations are rarely given, and when they do happen, they’re confusing.
A free radical is a molecule that has lost an electron, and in the context of health, this molecule is inside the human body. There are two main reasons this happens; toxins and/or natural metabolism. Either way, when a molecule loses an electron, it becomes unstable and it wants another electron.
There are many pairs of electrons in a molecule. When one electron in a pair goes astray, the remaining electron becomes an unpaired electron, and this results in molecular instability. The solution to the molecular instability is to take an electron from a neighboring molecule, so that the unpaired electron may be paired again.
While this solves the first molecules problem, the second molecule in the line that lost its electron is new free radical. This sets off a chain reaction of molecules nabbing electrons from one another. And this is where the bad news comes in. This chain reaction is very violent at a cellular level, and has the potential to cause severe damage to the cell in which free radicals originated.
This is where antioxidant come in. Antioxidant are molecules that can lose electrons without themselves becoming free radicals. This means that whenever a molecule in your body loses an electron, these antioxidant have a ready supply. When a molecule loses an electron and becomes a free radical, it can get an electron from the antioxidant in order to prevent a neighboring molecule from losing one of its own.