In the supermarket I am bewildered by the array of shampoos. Is my hair normal, or dry? Do I need conditioner, or ‘frequent use’? Even in my usual brand there are six options, and altogether there must be 100 different shampoos on sale. This is consumer choice gone mad; we cannot need all these things.

Then I go to get my hair cut, and the stylist tries to sell me ‘product’. Why are these slimy unguents called ‘product’? What I do know is that none of them can make my hair more natural or more healthy – it is all natural and quite dead; so it can never be healthy, let alone more healthy.

Nevertheless, hair holds a load of secrets, and this Tuesday on BBC2 at 11.20 p.m. we learn – from his hair - all about Beethoven’s life and death.

One evening in 1980 I sat in a car park in Edinburgh listening to my good friend David Jones on the radio, explaining what he thought had brought about the death of Napoleon Bonaparte. After Waterloo, Napoleon had been exiled to the island of St Helena in the south Atlantic, and there he died in 1821. Recent examination of a lock of his hair showed an unusually large amount of arsenic. Could he have been poisoned?

Well, some people accumulate arsenic naturally, but there seemed to be too much for that in Napoleon’s hair; so perhaps one of his cooks had been surreptitiously putting arsenic in his curries, hoping he would not notice. But David suggested another possibility; could the arsenic have come from his wallpaper? A popular pigment at the time was Scheele’s Green, which contained a chemical called copper arsenite. In the warm damp conditions mould could attack this to release vapours containing arsenic, and Napoleon could have been breathing it in without realizing.

So David posed the question, on the radio, did anyone know what colour the wallpaper had been? Amazingly he was sent a specimen of the actual wallpaper; it was bright green, and it did contain arsenic. Was the case proven? No. Science is rarely as simple as that; other experts believe he died of cancer, or of a rare glandular disease called the Zollinger-Ellison syndrome. Nevertheless, I prefer to believe in simple chemistry and my good friend Dr Jones; I think Napoleon was poisoned by his wallpaper; the evidence is in his hair.