Why the heat puts us in a bad mood

We’ve all heard that sunny days get your spirits up, that they create a sense of wellbeing, that life is better in warm countries such as Spain… But what happens when the temperature is so high that you can’t even set foot outside your house, or sleep at night? What happens when you are so overpowered by the heat that you don’t feel like doing anything at all?

Spain has gone through 80 heat waves in the last 40 years, according to a report released a few weeks ago by the Spanish National Meteorological Agency. The worst one on record took place in July and August 2003.

Research has documented an increase in assault, rape and murder during heat waves in the United States

It is a well-known fact that the human body suffers in these conditions. In the fourth century BC, Hippocrates described how the wind can affect people, and suggested that epidemics could be linked to weather conditions.

The normal temperature of a human body at rest ranges between 36ºC and 37.5ºC, while the skin, which is in contact with the outside world, is around half a degree lower, according to the report Variables meteorológicas y salud (Meteorological variables and health), written by environmental health experts from the Madrid regional government.

The body’s ability to regulate its own temperature rests in the hypothalamus, which balances heat production and heat loss mechanisms by increasing heart rate and blood flow, accelerating breathing, and by sweating, notes the World Health Organization (WHO) in Health and Global Environmental Change, a report on the effects of heat waves on human health.

The effort required to adapt to the new temperature is always greater during the first heat wave of the year, because our bodies have not yet grown accustomed to the high temperatures. This effort is also considerably higher if the hot weather persists for several days and does not let up at night, or when there is a lot of humidity and no wind, the Spanish Health Ministry warns.

What happens to our bodies

Heat stroke, fainting, sun burns, existing diseases that get worse – the news is filled with summer horror stories. But excessive heat also has many other effects that do not make the headlines. Many small children get skin rashes caused by blocked sweat glands. Adults suffer from water retention, especially in the legs, while the loss of sodium and water from excessive sweating can lead to painful cramps. Spending a long time in hot temperatures, especially when standing up, can lead to heat exhaustion.

What happens to our minds

The heat wave that hit Spain in the summer of 2003 had a number of effects on people’s mental health. Heat increases irritability and triggers more aggressive behavior, according to research by Barcelona University psychiatry professor Antoni Bulbena and his team, who published their findings in the journal Psychiatric Services.

A study by La Unión health center in Murcia analyzed data from the emergency room at Román Alberca Psychiatric Hospital over nine years, and matched it with local weather reports. The results were surprising: on breezy days with easterly winds and on rainy days there was a spike in psychiatric emergencies, whereas cases of delirium increased when humidity rose above 60 percent, and obsessive-compulsive disorders grew when temperatures surpassed 30ºC.

Valentín Martínez-Otero, a doctor in psychology who teaches at Madrid’s Complutense University, says intense heat has a negative impact on mood. “It can trigger a feeling of weakness and fatigue, and can also lead to irritability, mood swings and, of course, there is the impact on the quality of your resting hours. When it’s really hot, it is hard to fall asleep, and that increases your overall fatigue and general discomfort during the day, which finally results in a bad mood.”

The effects of heat on sleep quality have been well documented in recent scientific studies, including one from Yokohama International University.

More violence

Climate change is also linked to rising violence across the globe. Researchers at Berkeley University in California analyzed 60 studies from all over the world containing data covering hundreds of years, and concluded that there was a “substantial” link between the weather and conflict. Examples include the rise in the number of domestic violence cases in India during periods of drought, and the increase in incidents of assault, rape and murder during heat waves in the United States.

The paper, which was published in Science, even suggests that high temperatures are tied to larger inter-group conflicts such as ethnic confrontation in Europe and civil war in Africa.

A traffic light for inner peace

Pablo Fernández de Arróyabe, vice-president of the International Society of Biometeorology and a lecturer at Cantabria University, believes the effects of climate on human health are predictable and have a triple component: the potential danger of the climate event in and of itself, the vulnerability of each individual because of their personal and social conditions, and real exposure to this situation.

With help from the GEOBIOMET Group at Cantabria University, Fernández de Arróyabe has developed OxyAlert Beta, a free cellphone application for Android that collects weather data from all over the world, measuring oxygen change in the atmosphere and displaying it as a risk system using the three colors of a traffic light.

“There are three alert levels for hypoxia and hyperoxia (too little or too much O2), and users are asked eight questions concerning their sleep quality, muscular pain and headaches,” he explains.

If the app shows a red light, it means be careful: the heat may be altering you inner peace. Drink a lot of water, use loose clothing and reduce your physical activity.