How walking in the searing 40C heat can be dangerous for even healthy hikers... as Dr Michael Mosley is found dead in Greece

Walking in high temperatures – the Greek isle of Symi has seen temperatures of between 35C and 40C in recent days – can be dangerous for even a healthy person not taking adequate precautions.

Heat can put a great deal of strain on the body as it struggles to maintain its normal temperature of 37C (97.6F).

It can cause heat cramps, exhaustion and feelings of confusion and nausea.

At its most extreme we can suffer heatstroke, which can bring on organ failure and prove fatal.

The body's main weapon to stop overheating is sweating. As sweat evaporates, it cools the body.

But humid conditions reduce the effectiveness of sweating as the moister the air, the less moisture can evaporate from the skin. As the body overheats – and heatstroke sets in – the ability to sweat shuts down, and the body's temperature can spiral higher.

Excessive sweating also puts a strain on the heart. It has to pump harder to send blood, which carries heat from within the body to the surface.

The danger mounts as the body's internal temperature heats up past its normal level. Between 39C and 40C, fatigue sets in as our brain tells our muscles to slow down.

Exhaustion occurs between 40C and 41C, as our organs begin to lose the ability to function. The next stage – when the body's temperature rises above 41C – is heatstroke.