Can a smell wake you up? © iStock

Can a smell wake you up?

It's much nicer to wake up to coffee in the morning than a waft of ammonia after fainting.

Asked by: Keith Stephenson, Walsall

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Smelling salts (ammonium carbonate) have been used since at least the 17th century to revive a patient from a faint. They work because the ammonia gas irritates the lungs and triggers an inhalation reflex, which alters the breathing patterns and elevates blood oxygen levels.

With ordinary sleep, it is quite possible to be woken by the smell of coffee or frying bacon, which stimulates the appetite and raises arousal levels.

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