They also found that in the older animals glucose supply did not return to normal until 30 minutes after the task was completed.

BBC: Thinking 'drains the brain'

There is no hard evidence that the same kinds of pheromones found in animals also exist in humans, said Charles Wysocki, researcher at the Monell Chemical Senses Center in Philadelphia, Pennsylvania, and adjunct professor at the University of Pennsylvania.

CNN: Sweat may give off stress signals, study says

They also found changes in the mix of cells within the animals' immune system itself.

ECONOMIST: Social status and health