A complete loss of smell, known as anosmia, can occur after a cold, sinus infection or even a bump to the head.

Anosmia affects the flavour of food. However, it isn't always permanent and may recover naturally or through exercises like 'smell training' to re-stimulate the olfactory system.

• Smells can alert us about danger - we're repulsed by the smell of sewage and rotting food.
• We don't all respond to odour molecules in the same way.
• Butyric acid contributes to the smell of both Parmesan cheese and vomit, so it may smell offputting or appealing, depending ...