Air conditioner makes you sick? What is the link between weather change and illness?

Apparently there is a link between changes in the weather to becoming more susceptible to the flu and other infections, but researchers claim this is only a circumstantial relationship. 

There is no question that winter is the season most identified with common colds and flu. But is there a casual connection between freezing air conditioners, cold weather and the proliferation of diseases?

lightning strikes a teddy bear and a virus

The short answer is that weather alone, however wintry, does not cause us to get ill. People living in northern Canada, Alaska, Iceland, or northern Sweden do not get more colds than those in Greece or other warm countries. 

The belief that cold weather may lead to illness must have evolved from confusion, similar to beliefs about the origin of Malaria. "Bad air around swamps" was for thousands of years thought to be the cause of malaria. Millions believed this, while mosquitoes had always been the real cause of the disease. 

The origin of the myth that cold weather causes common colds comes from an era when humans did not know what caused the disease. This is the way many myths were created and their original role was actually filling the void. 

One of the reasons for the persistence of this specific myth is none other than the name chosen for the disease - a common cold. But one of the main causes due to which the myth has persisted is that for years the common cold had no satisfactory explanation. 

The viruses that cause colds were identified only in the 1950s, although the disease has been known to mankind since ancient times. The precise and detailed medical description of a cold has appeared in an Egyptian medical papyrus, which was the earliest medical text found and written before the 16th century BC.

Yet, at the beginning of winter, hospitals fill up with patients with complications of influenza and colds. In the summer, too, many think air conditioners cause them to get ill. Both phenomena have a certain foothold in reality, but the link between changes in weather and disease is indirect or circumstantial. 

Even if this relationship is not yet fully agreed, one thing seems certain - temperature alone does not affect the risk of disease, because we do not get ill because of the cold but because of exposure to viruses and bacteria. 

The common cold is not caused by just one type of virus. The most common virus associated with the disease is the Rhinovirus. In addition, it can also be caused by viruses such as Coronavirus, Influenza virus, Adenoviruses, Respiratory Syncytial Virus (RSV) and more. Overall, more than 200 types and subtypes of viruses were associated with symptoms of the common cold.

So what is the link between cold weather and proliferation of viruses?

Temperature changes are accompanied by additional changes, which actually increase the risk of getting sick. Many studies report an increase in respiratory diseases and hospitalizations when temperatures drop. There are several reasons for this, the importance of which is not yet clear.

First, some viruses, including some cold viruses, thrive at low temperatures, and their chances of survival in humans, as well as the chances of infection, increase as temperature and humidity fall. 

This is coupled with the fact that in cold and dry weather, the mucous membranes of the nose and lungs tend to dry up, so the body is more vulnerable to attacks by pathogens such as viruses and bacteria.

In addition, during the winter people tend to stay indoors, which are usually not sufficiently ventilated, which increases the chances and the rate of infection if there is an ill person present in the same space. 

Finally, a comprehensive literature review from 2016 states that the main cause of disease when temperatures fall (unlike periods when the temperature is low but stable) is the awakening of dormant viruses in the body due to temperature changes in the carrier body.

Spring and summer diseases

As the weather warms up, we see an outbreak of other diseases, this time under the influence of seasonal allergies. As the body fights a typical spring allergy to pollen, it becomes much more vulnerable to attacks by viruses and bacteria.

In addition, no allergy attacks often show symptoms similar to the common cold. For example, Hay Fever (Rhinitis) is a concept born of what was once perceived as a disease that would break out among farmers during the harvest season at the end of the summer. 

In retrospect, it turned out that this was a severe allergy attack and not a viral or bacterial disease as they had previously thought. There are many other diseases that thrive at high temperatures, gastrointestinal infections such as Salmonella, Shigella, and Campylobacter are prime examples.

Like other pathogenic bacteria that work in the digestive system, Campylobacter enters the body through spoiled food, especially improperly cooked chicken. It causes fever and diarrhea lasting several days, and sometimes there will also be reactive arthritis and sensitive intestine. 

In rare cases, it can even lead to the severe neurological Gillian-Barres syndrome, which causes muscle paralysis. The number of patients due to the Campylobacter bacteria tripled in the years 1999-2010 and its current rate is 91 patients per 100,000 people. 

The disease is most common in infants younger than two years of age, and the rate of the disease among toddlers is about 350 per 100,000.

In a joint study conducted by Tel Aviv University, the University of Haifa and the Israeli Ministry of Health, the association between Campylobacter virus infections and temperature in Israel was examined to determine whether heat contributes to the spread of the disease. The results of the study proved that such a relationship exists.

The study found that when temperatures rise, so does the incidence of infection. On average for the entire population, starting at a temperature of 27 degrees, there is an increase of about 16 percent in cases of disease for each degree. 

Even more alarming is the fact that for toddlers aged 2 years and under, this relationship is valid for the entire temperature range, i.e., there is no threshold temperature, and any warming of one degree leads to an increase in the percentage of infections, which is about 5 percent. Toddlers are more affected than adults because their immune system at this age is not yet developed and therefore cannot develop immunity to the disease.

How can the relationship between weather and food poisoning be explained?

Food undergoes a long production cycle from its growth in the economy until it reaches the consumer. 

Risk factors may increase at any stage of the production cycle, from low density and hygiene in poultry farms, through cross-contamination in slaughterhouses (i.e., between the birds themselves) and suboptimal transport and storage conditions. 

The effect of all these increases as temperatures rise. The study found that the rate of morbidity in Israel is strongest linked to the temperature in the four weeks prior to diagnosis, suggesting that the infection takes place in the later stages of the food production process - around the time of transport, storage or consumption.

These conclusions reinforce similar findings from studies conducted in other countries around the world; the same association between warming and the spread of Campylobacter was also found in Canada, England and Australia. 

A comprehensive international scientific review recently published examined hundreds of studies from the last decade that dealt with how climate change affects human health. 

According to the survey, there is widespread scientific consensus that warming over 2 degrees Celsius above the pre-industrial average (the global target set in the Paris Agreement of December 2015) poses significant health risks. These are mainly due to heat loads, concentrations of ozone near the ground, and damage to food availability and quality.

Do air conditioners make people more susceptible to infections?

As for air conditioners, there is a phenomenon known as the sick building syndrome; it has been observed that people who live or work in buildings that are built in a certain way report headaches, fatigue and nausea during their stay in the building. 

One of the reasons for this phenomenon is inadequate ventilation, and of course the use of air conditioners.

Here, too, the temperature of the air conditioner itself is not the cause of the disease, but the air conditioner, which is not cleaned frequently, accumulates moisture that provides fertile ground for the development of fungi and bacteria. 

Some are emitted from the air conditioner and carry in the air and can cause problems in the respiratory system. In addition, the air conditioner recycles the air inside the room or building and does not introduce new air. 

So harmful substances and bacteria are distributed within the air-conditioned space. Finally, the air conditioner dries the air in the room, and as mentioned above, dry air increases the body's vulnerability to bacteria and viruses.