Every time the weather heats up in Hong Kong, hospital admissions increase correspondingly. Summer temperatures can often be brutal, and global climate change has made the mercury rise even higher in recent years, leading to greater incidences of heat-related illnesses.
A study conducted between 1998 and 2009, and published online in the Bulletin of the World Health Organisation, uncovered a link between weather phenomena and pollution levels, and hospital admissions.
Out of the more than 7.9 million hospital admissions that were recorded during the 11-year study period, 33 per cent of them took place during the hot season. During this season, admissions increased by 4.5 per cent for every increase of one degree Celsius above 29 degrees, with respiratory ailments accounting for most of those hospitalised.
Heat illness refers to disorders that are caused by environmental heat exposure. Besides heat stroke - which is life threatening - heat illnesses include heat rash or "prickly heat", heat cramps, heat syncope and heat exhaustion. Up to a certain degree, physical activity in warm or hot weather is harmless. When the body overheats, natural processes kick in to help bring down its core temperature.
Sweating occurs, which cools the body directly as the moisture evaporates from the skin. Dermal blood vessels dilate, bringing more blood out to the body's periphery and transporting excess heat to the surface of the skin, where it is released. Overall, the body has to work harder to protect it from the dangers associated with overheating.
But when the ambient temperature is too high, the body's cooling processes can become ineffective. Heat dissipation is reduced, and, if humidity is high and there is no breeze, the vapour barrier can prevent the sweat from evaporating from the skin, says Dr Hans Schrader, executive medical director at Matilda International Hospital.
In some cases, the blood vessels under the skin are unable to open fully, or one's sweating ability is reduced. "When the combination of temperature and humidity goes above a certain threshold, and the body temperature increases to 38 degrees or higher, this may cause harm to the body's cells, and eventually to crucial organs, such as the kidneys, brain and heart," Schrader adds.
There are several risk factors for heat illnesses, says Schrader. Strenuous activity in high humidity and high temperatures is an obvious one. Carrying out any strenuous activity in thick or full clothing increases your risk significantly, as it reduces the body's ability to sweat and to radiate heat.
This is why heatstroke is a common problem for American football players. Poor physical fitness, too, can lead to overheating, as it increases exertion and heat production.
Overweight and obese people are more likely to suffer from heat illnesses than those of optimal weight. Excess fat increases the body's insulation layer, making it more difficult for heat to escape the body, Schrader explains. The elderly are also vulnerable, as thermoregulatory capacity is impaired with ageing. Those suffering from chronic health conditions like heart disease or high blood pressure, or infections such as cold and flu, may have impaired thermoregulation ability as well.
Other risk factors include dehydration, as this reduces the ability to sweat, and taking medications that reduce sweating, or that constrict the blood vessels. These include antihistamines, decongestants, and certain types of anti-depressant, anti-hypertensive and anti-epileptic medications, adds Schrader.
During a heat wave, babies, young children and disabled individuals also need extra attention to ensure that they are properly hydrated, and that their thermal environment is regulated.
Athletes, and professionals who work outdoors or who perform physically demanding duties, such as firefighters, construction workers, those in the military, and people working in boiler rooms, foundries or catering kitchens, are another group at high risk of heat-related illnesses.
Fortunately, there are several ways to prevent heat illnesses. The Centre for Health Protection urges Hongkongers to prepare for the hot season by keeping hydrated, especially while taking part in strenuous or outdoor activities. Water is preferable to coffee, tea or alcohol, which can have a dehydrating effect.
Fruits and vegetables with a high water content - such as watermelon, cucumber and tomatoes - can provide extra hydration throughout the day.
It also helps to limit prolonged activities that can tax on the body, for example, hiking or trekking. If taking part in outdoor activities, schedule them for the early morning or late afternoon, when the heat from the sun is not so intense. When exercising indoors, make sure the area is cool or well ventilated to increase air flow. Schrader stresses the importance of taking regular breaks when exercising to rest and rehydrate.
Wearing loose, light-coloured clothing is also recommended, to reduce heat absorption and facilitate sweat evaporation. When outdoors, sun protection is a must. Keep your head cool by wearing a wide-brim hat or using an umbrella, remain in the shade if possible, apply a sunscreen, and shield your eyes with UV radiation-blocking sunglasses.
If you feel unwell while exercising outdoors, or if the heat feels unbearable, Schrader advises to stop what you are doing and rest in a ventilated and well-shaded area. Cool down internally by drinking water, and spray cold water on exposed parts of the body to bring down the temperature of your skin.
If the discomfort persists, seek medical attention.
How to recognise heat-related illnesses
Heat rash or "prickly heat"
Symptoms: small, red, itchy and inflamed papules on the face, neck, upper chest, groin and scrotal areas.
Characteristics: this is a skin irritation caused by excessive sweating, and tends to be common in young children.
Symptoms: muscle pain and spasms in the arms or legs, or abdomen.
Characteristics: the cramps are caused by muscle fatigue and loss of electrolytes through heavy sweating. It typically occurs during relaxation after prolonged strenuous activity in a hot environment.
Symptoms: dizziness or fainting.
Characteristics: when there is increased blood flow to the skin and pooling of blood in the legs, blood flow to the brain is reduced. The dizziness or fainting usually occurs during a sudden rise from a sitting or lying position.
Symptoms: elevated core body temperature (between 37 and 40 degrees Celsius), pale complexion and profuse sweating, intense thirst, rapid pulse and shallow breathing, muscle cramps and generalised weakness, headache, nausea, vomiting, dizziness and fainting.
Characteristics: this condition is caused by water and/or electrolyte depletion from exposure to heat or strenuous activity. Heat exhaustion is serious and can develop into heatstroke.
Symptoms: very high core body temperature of 40 degrees or higher, red, hot and dry skin with no sweating, dry swollen tongue, rapid pulse and shallow breathing, headache, nausea, seizure, confusion or disorientation, unconsciousness or coma.
Characteristics: when the body's core temperature becomes extremely high, its internal systems shut down. Immediate medical attention is required.