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Object lesson No 38

Many naughty things come out of bottles. Wine, for one. Lager, full-fat milk, and garlic pickle. Not to mention peroxide blondes.

Aged 17, I was desperate to join the ranks of women-who-were-not-quite-as-good-as-they-ought-to-be. Eventually, I hit the bottle and went platinum. As I hung on the telephone to my boyfriend I thought of blonde punk icon Debbie Harry. My parents thought of big bills and lost innocence.

I didn't concern myself with what had actually happened to my mid-brown mop - probably the only thing I have in common with Marilyn Monroe, Jean Harlow, Jerry Hall and star rugby player Thomas Castaign de. Yet a moment's investigation would have revealed that these trademark locks are courtesy of a loose connection in a chemical called hydrogen peroxide.

At room temperature hydrogen peroxide is a syrupy liquid 40 per cent denser than water. Its chemical formula is H2O2, which means it is made up of two hydrogen and two oxygen atoms. Because the two oxygen atoms are only weakly bonded, the chemical easily breaks down into H and HO2 or into two OHs. These so-called free radicals are keen to shed their oxygen atoms, making them powerful "oxidising" agets.

When we put them on our hair they oxidise pigments called melanins. These are the polymers that determine skin, eye and hair colour and react with sunlight to help us tan. The hydrogen peroxide smashes the double bonds in the melanin, bonds that allow the pigment to absorb light and give it colour. With them gone, the result is hair that is whiter than white.

This process doesn't just work on hair. Hydrogen peroxide, 1.5 million tons of which is produced globally every year, is used on wood pulp to make white paper and to bleach textiles and leather.

It is also an antiseptic. An enzyme in the blood causes H2O2 to decompose into water and oxygen when applied to a cut. It foams impressively in the process which brings any dirt to the surface. Before people had the genuine article they used to dress wounds with honey - which contains traces of H2O2.

Here endeth the chemistry lesson. You may not think it is rocket science, but you would be wrong. Such is the power of pure H2O2 that it is used to make rocket fuel. Thus the chemical that represented one small step for a brown-haired woman was also right there for that one big step for mankind.

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