How can I get sick when I am so clean?

Recently, there was a very popular game called Plague Inc., Players can create an infectious disease to destroy all human beings and experience the pleasure of being a god of death. However, the game also contains some interesting biomedical phenomena. For example, to let your germs invade western countries rich in medical resources, the evolution of [allergy] ability is almost one of the necessary killers.

This setting of the game is not completely groundless, In fact, allergic diseases such as allergic rhinitis and asthma do prefer developed countries and regions. Particularly children in those areas, The prevalence rate is significantly higher than that of developing countries and regions. According to the survey results of the International Child Asthma and Allergic Diseases Research Program (ISAAC), In 1996, the prevalence rate of asthma among British children aged 13-14 years old was as high as 20.9%, while the prevalence rate of asthma among children in India was only 1.6% at the same time. The prevalence rate of asthma among children in mainland China was about 2%, with Beijing, Shanghai and other economically developed areas being higher, while the prevalence rate in Tibet plateau was only about 0.5%.

The prevalence of allergies in developed countries, As a result, if the protagonists in American and English dramas do not have many allergies, it will make people feel unreal. For example, Howard, the obscene man in the Big Bang Theory, will swell up a sexy [sausage mouth] as long as he eats peanuts, which is a typical manifestation of food allergy. So why is the prevalence rate of allergic diseases higher in developed regions?

Experts said: [Because they live too clean! [This is not the nonsense of [brick experts], but is based on research.

Let’s first review the epidemic history of allergic diseases:

The United States and Britain reported in 1872 and 1873 respectively that ragweed, a species native to North America, Seasonal inflammation of the upper respiratory tract mucosa caused by pollen from weeds all over the world today, The name of his life is “hay fever” or “pollinosis”. This is the earliest description of pollen-induced allergic rhinitis. The situation became more and more serious later. At the beginning of the 20th century, many patients took refuge in the Island of Heligoland in Germany, which is located in the southeast of the North Sea in Europe, every summer to avoid these annoying pollen. Interestingly, the [hay fever] in this period was almost the [exclusive disease] of the rich, while the working class, especially the farmers, rarely got the disease.

By around 1930, The further spread of hay fever prompted the establishment of a sub-specialty of allergic diseases. At its worst, People take to the streets to sneeze. In order to control [hay fever], New York City launched a nationwide campaign to eliminate ragweed in 1946, but the number of people suffering from allergic rhinitis continued to rise. By the 1950s, the prevalence rate of the population in New York City had reached about 10%, and this [nationwide weeding campaign] was finally abolished in 1952 due to limited results.

From the 1960s to the 1990s, the prevalence rate of allergic rhinitis in western countries rose steadily, basically maintaining between 15% and 20%. At the same time, asthma began to spread, and the prevalence rate of asthma in western countries at the end of the 20th century was at least 10 times that in 1960.

The question is, after the middle of the 19th century, what occurred in western countries, leading to the prevalence of allergic diseases?

The problem mainly occurred in the changes in the sanitary environment: in the middle and late 19th century, drinking water sanitation was highly valued in North America and Europe, and a large number of measures such as the construction of sewers and sewage treatment systems completely separated drinking water from domestic and production sewage in western countries, which greatly reduced the incidence of intestinal infectious diseases.

At the beginning of the 20th century, the health conditions in western countries further improved, mainly including:

1. The relocation of animal husbandry from major cities and towns has greatly reduced the chances of urban population suffering from zoonotic diseases;

2. Carry out chlorination disinfection of drinking water;

3. Parasites and malaria have been significantly controlled.

These changes have resulted in a combination of infectious diseases, In particular, the mortality rate of intestinal diseases and tuberculosis has dropped by as much as 90%. This period is the period when allergic rhinitis mentioned above [develops and expands]. When the epidemic situation of allergic rhinitis stabilizes, Asthma followed. The prevalence of asthma in the late 20th century, This may be mainly related to the widespread use of broad-spectrum antibiotics, the further decline in hepatitis a infection rate and the popularity of vaccines during this period. Similarly, in the late 20th century, when the economies of some developing countries began to take off and some areas began to improve health conditions, allergic diseases began to gradually spread in these areas.

The correlation between improved sanitary conditions and the prevalence of allergic diseases has prompted researchers to put forward an interesting theory-[Hygiene Hypothesis]: the better sanitary conditions, the less exposure to various microorganisms/pathogens in childhood, and the higher the probability of allergic diseases in growth.

The evidence comes from British epidemiologist Strachan, He observed that, Children with siblings are less susceptible to allergies, Because of the large population in the family, Children are also more likely to develop recurrent infections, suggesting that exposure to microorganisms in early childhood is a protective factor for allergic diseases in adults. U.S. Researchers also found that infants who go to day care centers within half a year have an increased chance of developing various infections, but the prevalence of asthma at the age of 6 decreases accordingly.

In fact, every healthy person has more than 100 trillion viruses, bacteria, fungi and other microorganisms. The complex interaction between human body and these microorganisms directly or indirectly promotes us to better adapt to the living environment.

These microorganisms are also enemies and friends.

[Friends] They can regulate the immune system of the human body, help the immune system develop and mature, and regulate other physiological functions of the human body through the [neural-immune-endocrine network]. Normal flora can also help the body resist the invasion of various pathogenic bacteria.

[Enemy] is manifested in that once the symbiotic balance between human body and microorganisms is broken, various diseases may occur in the body. In recent years, studies have even found that microorganisms can affect the behavior of animals, and even some researchers have pointed out that [each of us is actually the result of the action of microorganisms], [the importance of microorganisms is comparable to that of genes].

The improvement of sanitary conditions has objectively reduced the risk of human suffering from various infectious diseases, but it is a bit overkill to be too clean, turn pale at the mention of [bacteria], and declare war on all microorganisms with various antibiotics and disinfectants.

For example, because children born by caesarean section do not obtain protective microorganisms through vagina, the diversity of intestinal flora is not as good as that of children born smoothly, and the risk of various food allergies increases accordingly when they grow up.

Another example is that premature and excessive use of antibacterial drugs in infants will destroy the ecological structure of normal flora and induce allergic constitution. Not only that, if the immune system lacks antigen stimulation before maturity, the tolerance mechanism of the immune system will be broken, and the body [is not divided between ourselves and the enemy], which is more likely to lead to [autoimmune diseases] such as type I diabetes.

Of course, correlation is not equivalent to cause and effect, and there is still much room for improvement in the [hygiene hypothesis]. At the same time, other theories have been put forward to explain the prevalence of allergic diseases.

For example, the increase of room temperature and humidity is conducive to the breeding of indoor allergens such as dust mites, while the change of people’s living habits and the decrease of outdoor sports increase the chance of getting rough with indoor allergens, as well as mental stress, pollution, genetic factors, etc., which may be the causes of more and more common allergic diseases.

Therefore, when I was a child, I played with mud and got in touch with some Xiao Mao puppies. [Dirty] gave the immune system enough opportunities to exercise. When I grew up, my body would not go to war with any foreign bodies. It is not certain that my body would be healthier.