How Humans Coped with Heatwaves Before Air Conditioning

When heatwaves strike, many people immediately turn to air conditioning or cold drinks. However, scientific research shows that several traditional methods used for centuries are effective at keeping the body cool.

In Japan, the tradition of uchimizu involves sprinkling water on streets and pavements. A 2018 study published in the journal Water found that this practice can lower ground-level air temperatures by about 5.5 degrees Celsius through evaporative cooling, even with a small amount of water. Shigenori Asai, director of the Japan Water Forum, noted the effect is amplified when entire communities participate.

Before air conditioning, people in hot regions of India used tirai, or curtains, made from vetiver roots. These were soaked in water and hung in doorways or windows facing the wind. As hot air passed through the wet curtain, heat was absorbed by evaporation, cooling the incoming breeze. The roots also emitted a pleasant fragrance. This simple technology has inspired modern indirect evaporative cooling systems used in some data centres, which are more energy-efficient than conventional air conditioning.

Wearing loose, dark-coloured clothing might seem counterintuitive in the heat, but it has been a practice in the Middle East and North Africa for centuries. A 1980 study published in Nature found that loose black robes help keep the body cool. While the fabric absorbs solar heat, the hot air inside the garment rises and escapes from the top, drawing in cooler air from below and creating a natural circulation. Researchers concluded that the extra heat absorbed by the black clothing dissipates before reaching the skin. Similarly, seersucker, a thin, puckered cotton fabric popular in the southern United States, is effective because it does not stick to sweaty skin and creates small air pockets that aid circulation.

Eating spicy food can also help the body feel cooler. Chillies contain capsaicin, which stimulates heat receptors in the mouth, tricking the brain into thinking the body is overheating. In response, the body widens blood vessels and increases sweat production to accelerate cooling through evaporation. This is one reason why cuisines in hot countries like India, Thailand, and Mexico are often spicy. Conversely, sugary cold drinks are not recommended as they can reduce the body’s natural sweating reflex, and digesting sugar generates additional body heat. In many Asian countries, people prefer unsweetened tea made from plants like barley, which helps maintain hydration and improves blood flow, allowing heat to be released more easily through the skin. Alcoholic drinks like beer are also discouraged during hot weather as they can cause dehydration and impair the body’s ability to regulate temperature.

Finally, the siesta, or midday nap, traditionally practised in Southern European countries like Greece, Spain, and Italy, offers benefits during extreme heat. The body generates heat through movement and energy processing, so strenuous activity during peak temperatures increases the risk of heat exhaustion. As European summers become more extreme, experts are encouraging a revival of this midday rest. In 2023, the then-head of the German National Association of Doctors suggested European countries adopt working patterns from hotter regions that include a break during the hottest part of the day.