Most people remember fondly the Mad Hatter from Alice In Wonderland, but the phrase mad as a hatter was around before Lewis Carroll created his crazy character.

Felt hats were very popular in Europe and North America from the 1500s to the 1800s, particularly top hats, the best of which were made from beaver fur.

In a very complicated process, the hatters worked in small badly ventilated workshops and came into contact with many poisonous substances to create these stylish fashion items for the well-to-do. Mercury was the main offender, which led to what became known as ‘mad hatter’s syndrome’.

Symptoms of mercury poisoning are now well documented. They include trembling (hatter’s shakes), loss of teeth, slurred speech, depression, memory loss and personality changes.

It all makes the Mad Hatter’s tea party look quite sane!