Heatstroke occurs when the temperature of the body rises sharply. This may happen because of excessively high outside temperatures, physical exertion, extensive burns, and severe sunburn or because of an undiagnosed medical condition such as an overactive thyroid gland.

The heat can affect anyone, but some people are at greater risk of serious harm. These include:

• older people,
• babies and young children,
• people with a serious chronic condition, particularly breathing or heart problems,
• people with mobility problems,
• people who are physically active, like manual workers and sportsmen and women.

Certain medications can also make you more susceptible to heat exhaustion. These include:

• diuretics - these drugs increase the production of urine, so they can add to dehydration,
• lithium, anti-epileptics, statins - these may not work properly if you get dehydrated,
• beta-blockers - these drugs help reduce blood pressure but they also interfere with the body's processes of thermoregulation (how it copes with getting too hot), such as sweating.

Contact your doctor or pharmacist if you are worried about your health during a heatwave, especially if you are taking medication or have any unusual symptoms.