A small number of people suffer from Moebius Syndrome, which means that they are physically unable to smile. The condition affects the nerves that help us smile, frown, blink and perform other facial expressions.

Charles Darwin was one of the first to suggest our expressions may actually intensify our feelings. This theory is known as the 'feedback loop' or 'facial feedback hypothesis'. A smiling expression feeds back into how we experience mood, therefore making us feel happier or a joke seem funnier. Professor Fritz Strack, along with Leonard L Martin and Sabine Stepper, investigated this theory and published a study in 1988. This revealed that people who used their smiling muscles when presented with cartoons found them more amusing than people who didn't.

Mark Stibich, PhD, a consultant at Columbia University believes smiling may also act as a stress relief.'When you're stressed a number of things happen to your body. Your pulse rate shoots up, your digestive system shuts down, and your blood sugar levels increase. But two things also happen that you have voluntary control over - your breathing becomes shallower and faster and facial expressions kick in. If you can slow your breathing down and change your expression, you may be able to turn around the stress cascade.'

If you're feeling low or depressed, there are lots of people who can help you, especially if you'd prefer to speak to someone impartial. Talk to your GP who can refer you to a counsellor, cognitive behavioural therapist or psychologist.

You can also speak to trained professionals at Saneline on 0845 767 800, or Mind on 0845 766 0163.