Not clean or sick?

In the age when microorganisms were not known to cause diseases, people’s concept of cleanliness was only visual cleanliness. Even doctors are the same. A famous American doctor said this: Doctors are gentlemen, and gentlemen’s hands are clean.

Since Lewenhoek saw microorganisms under a microscope, Pasteur, Liszt and others have established disinfection methods, and the whole society has begun to cultivate the habit of hygiene.

However, in recent years, the saying that one is not sick until one is unclean has suddenly risen, and a theoretical basis has been found to teach parents not to pay too much attention to hygiene when taking care of their children. What is going on?

The cleaner you are, the more susceptible you are to allergies

It all started in 1989, David Strachan, a British epidemiologist, published a paper in the British Medical Journal: According to epidemiological data, Compared with only children, children in large families are at lower risk of pollen allergy and eczema. From this, it is deduced that children in large families are exposed to more sources of infection from their brothers and sisters, thus avoiding allergic diseases, thus putting forward the [hygiene hypothesis], reducing the chance of infection in childhood, and being the root cause of allergic disease outbreaks in the 20th century.

One stone stirred up thousands of waves.

After the Hygiene Hypothesis came out, it was accepted by many immunologists and epidemiologists, and a lot of research was done to obtain the support of epidemiological data, as well as some laboratory and animal experimental evidence to support this view.

For example, compare the incidence of chronic allergic diseases between developing countries and developed countries. For example, the incidence of allergic diseases increases after emigrating from developing countries to developed countries.

A study found that the use of dishwashers is related to the occurrence of allergic diseases, because hand-washed dishes are not clean, children are more exposed to bacteria and reduce the incidence of allergic diseases.

At present, the health hypothesis extends from allergic diseases to type 1 diabetes, multiple sclerosis, depression, some tumors, autism and other diseases.

The health hypothesis has been in existence for more than 25 years and is still at the level of hypothesis. I think that although there are some data to support it, there is no hard evidence and further research and verification are needed.

There is no mature immune system?

On the basis of the hygiene hypothesis, the “old friend hypothesis” appeared.

The old friend hypothesis holds that in the long era of hunting and gathering, the human immune system was driven by microorganisms in the environment and evolved.

After entering the agricultural era, this kind of drive does not exist, so people’s immune function has not developed and matured after the agricultural era.

On this basis, coupled with the impact of the health revolution, allergic diseases have increased significantly.

In my opinion, the old friend hypothesis is more reliable than the hygiene hypothesis and has theoretical support. However, the most realistic problem of this hypothesis is that it cannot provide a solution. Unless we return to the era of hunting and gathering, we can only continue like this regardless of whether the immune function is mature or not.

Is intestinal bacteria the key?

In 2010, the [Microbial Diversity Hypothesis] appeared again, believing that intestinal flora is the driving force for the development of immune system, and the key time is from the third trimester of pregnancy to the first few months of birth.

Natural childbirth and breast-feeding can help the establishment of intestinal flora and prevent allergic diseases.

The microbial diversity hypothesis is more practical than the old friend hypothesis and has solutions, such as natural production and exclusive breastfeeding.

The question to be answered by these three theories is why there have been more and more allergic diseases in the past few decades. The core view is that they are not clean. Although there is no definite conclusion, they also have their own markets in China and are sought after by some people in the industry, causing great confusion to the public.

The hypothesis that only trees can be seen but no forests can be seen.

In my opinion, the biggest problem with these hygiene hypotheses is that only trees can be seen but forests cannot be seen.

First of all, allergic diseases do involve many children, but allergic diseases do not represent all children’s diseases. From the perspective of protecting children’s health, infectious diseases, especially respiratory infectious diseases, are the greatest threat. Besides vaccines, hygiene is also an extremely effective prevention method to prevent infectious diseases.

In order to prevent possible allergic diseases without hygiene, children are exposed to pathogenic microorganisms, and the consequences are beyond control.

Even from the perspective of cultivating immunity, it is only possible that a few children have improved their immunity to pathogenic microorganisms through contact with microorganisms and illness. Most children will only suffer from continuous illness and physical weakness, affecting their health and life span.

Secondly, even if it is limited to allergic diseases, these hypotheses may not hold water. Hygiene has been talked about for a long time, and the rapid rise in allergic diseases did not appear until long after hygiene was talked about.

As far as microorganisms are concerned, the correlation between hygiene and the rise of allergic diseases may not be as strong as the correlation between antibiotic abuse and allergic diseases. The past few decades have been the decades of antibiotic abuse.

In addition to antibiotics, there are also our eating habits. The past few decades have been the decades of human diet garbage, which has led to obesity in the whole population. This change in eating habits is more likely to lead to a high incidence of allergic diseases, which better explains the difference in the incidence of allergic diseases between developed and developing countries.

In addition, there are factors of lack of exercise. One side effect of the information revolution is that people are getting lazier and lazier. Lack of activities, especially outdoor activities, will lead to a rapid rise in allergic diseases?

All this is worth considering and studying. The rapid rise of allergic diseases may be caused by the combined effect of the above factors. Among these factors, the lack of contact with microorganisms is probably not so important.

Another problem with the Hygiene Hypothesis, Is to exaggerate the effect of cleaning, It is believed that cleaning can achieve sterile effect. In fact, the cleaning we do today cannot make us live in a sterile environment. Even if the living environment is completely disinfected, microorganisms will soon come back, blown by air, brought by dust and food, brought by people, etc. The real chance of infectious diseases can be reduced not only by cleaning the living environment, but also by washing hands frequently.

Can’t you enhance your immunity?

Many people from an immunological point of view, Agree with the hygiene hypothesis. If we look at a single microorganism, Early exposure does produce resistance, but there are two problems. One is that such exposure can lead to serious diseases. The other is that there are so many microorganisms in the environment that you cannot master exposure to what. Good microorganisms and bad microorganisms exist at the same time in the environment, and you cannot choose to contact only good microorganisms.

The topic of enhancing immunity is popular with some medical professionals, But they only see the immune system’s response to a single microorganism. The immune system has to deal with countless microorganisms, so the immune system needs to maintain a state of balance, which should be alert to harmful microorganisms and indifferent to harmless microorganisms. Once this balance is destroyed, the immune system’s response will be unpredictable.

I don’t advocate being unclean to enhance immunity. For some high-risk groups, their immune system itself has defects. If they become ill after being unclean, they will cause permanent damage to the body.


According to epidemiological data, people with healthy living habits have normal and strong immune function, while people with bad living habits such as alcoholism, unhealthy diet and high pressure have relatively weak immune function and are prone to illness. Therefore, enhancing immune function depends on healthy living habits, not intentional illness.

Infectious diseases are still the greatest threat to human health. Our primary goal is to take corresponding measures to reduce the probability of adults and children suffering from infectious diseases.

When I was still in school, my immunization teacher said that catching a cold several times a year could enhance my immune function, so I felt at ease and got sick several times a year, one or two of which could not even get up from bed. The more sick I became, the more sick I loved to get sick. After arriving in the United States, I changed my living habits and stopped abusing drugs. I only got sick once a few years, and every time I was very mild.

Be clean, not dirty.