David Salinger is one of the world's leading trichologists - or hair and scalp specialists - and is director of the International Association of Trichologists.

He says: there is conclusive proof that stress can cause excessive hair loss. One substance that can have an adverse effect on hair in times of stress is the neuropeptide substance P, or SP for short. An increase in SP leads to inflammation of nerves around the hair follicles which in turn leads to excessive hair loss.

"We can counteract the effects of SP with vitamin D, which you can obtain from the sun, and from foods such as fish, eggs, and liver.