SkincareFree radicals

Free radicals are highly reactive atoms that have one unpaired electron. They are unstable as there is a tendency for unpaired electrons to pair up and so the free radicals react very quickly.

Radicals can be formed when a covalent bond is broken by energy supplied by UV light. Due to their reactivity, they are able to cause chain reactions, as they often react to produce other free radicals. These reactions happen in a three stage process.

Stage one: Initiation

The dot next to each of the bromine atoms in the above equation represents the unpaired electron each has from the shared pair of the covalent bond. Dividing one bromine molecule produces two highly reactive radicals.

While UV light is needed to begin the process, further reactions do not need UV light, and so the chain reaction can continue, even in total darkness.

Stage two: Propagation

The highly reactive radicals formed can remove atoms from other (stable) compounds to re-establish stable covalent bonds. This reaction will produce a new free radical.

For example, a bromine radical can react with an alkane, like methane.

The new radical formed can in turn react with another bromine molecule. This is also a propagation step as it also generates a radical product.

Stage three: Termination

The chain reaction will only end when a reaction takes place in which no new radicals are formed. This can occur whenever radicals react with each other.

For example, a bromine radical can react with an alkane, like methane.

Free radical scavengers

Free radical scavengers are chemicals (usually vitamins, minerals or enzymes) that react with and destroy free radicals.

This is often desirable to help protect our skin (so they are present in cosmetics) and our food (present both in some foods and in plastics).

By reacting with any free radicals present, the free radical scavengers prevent a chain reaction from occurring.