Heatwave health risks: From dehydration to heat stroke

A Doctor Writes: Health effects of hot weather linked to the body’s ability to adapt

It's official: heatwave conditions have been met, we can expect temperatures in excess of 30 degrees Celsius and Met Éireann has declared a countrywide yellow heat warning. So what are the main health risks posed by a heatwave ?

Dehydration, when the body doesn’t have enough water is one risk; overheating is another – it can make symptoms worse for people with chronic heart or lung problems; heat exhaustion; and finally heat stroke.

The health effects of hot weather are linked to the body’s ability to adapt to heat by acting as a natural cooling system. The main ways in which the human body eliminates heat during thermal stress are through sweat production, increased cardiac output and redirection of blood flow to the skin. These responses can be diminished or delayed in older people or other susceptible groups such as those with chronic illness or people taking certain drugs. Young children are also more susceptible to the negative effects of prolonged heat.

Are there particular diseases that cause additional problems during a heatwave?

If you have had a heart attack, a stroke or suffer with chronic obstructive pulmonary disease, extra caution is needed. High levels of air pollution, coupled with warm weather, have been shown to increase the number of strokes by 50 per cent. Asthma sufferers are vulnerable to high pollen counts. And people with diabetes, neurological disorders and psychological illnesses may also be at increased risk.


Those taking drugs such as diuretics which are designed to get rid of body fluids may benefit from a reduced dose during a heatwave. Seek medical advice first.

What should you look out for in someone who is overheating dangerously?

Excessive thirst, nausea, vomiting and muscle cramps are signs of heat exhaustion. Untreated, it progresses to heatstroke: watch out for heavy sweating that suddenly stops; a rapid heart rate and rapid breathing; and neurological symptoms such as confusion and a loss of co-ordination. Heatstroke is a medical emergency that requires urgent medical attention.

Have you any tips for avoiding the worst effects of a heatwave?

Avoid being outdoors between 11 am and 3 pm.

If you know you are vulnerable to the effects of heat, then move to a cool room and rest.

Close curtains in rooms that face the sun to keep indoor space cool.

If you do not have access to air-conditioning then stay indoors on the lowest floor in a well ventilated area with fans.

Take a cool bath or shower.

Change into loose, light coloured clothing.

Limit outdoor exercise and work, especially in the hottest part of the day

Drink plenty of water or dilute fruit juice. Don’t wait until you feel thirsty.

Avoid alcohol and caffeinated drinks as they increase dehydration.

When you are out and about, wear a hat, apply lots of sunscreen and walk on the shady side of the street.

Take water with you when you go out and when travelling.

If you are heading to the water to cool down, heed local safety advice. Never leave an infant or a child in a parked car.

Muiris Houston

Dr Muiris Houston

Dr Muiris Houston is medical journalist, health analyst and Irish Times contributor