By Megan (Frederick) Amason
Allergy and autoimmunity on the rise
In recent years, doctors have noticed an alarming trend: the number of individuals diagnosed with allergies or an autoimmune disease has increased drastically. Each year, around 50 million people in the United States suffer from allergies: a range of symptoms caused by a reaction to non-harmful, “foreign” substances, such as pollen or pet dander. Similarly, around 23.5 million people have been diagnosed with an autoimmune disease such as lupus, type I diabetes, or rheumatoid arthritis, meaning that their immune systems have targeted healthy, “self” proteins that are part of their bodies. In both instances, the person’s immune system has gone haywire and can no longer protect them from pathogens. Instead, the immune system harms the body in the absence of infection.
Basis for the hygiene hypothesis
Why are so many people experiencing illnesses caused by overactive immune responses? Scientists think they have an answer, and it’s been called the “hygiene hypothesis”. Originally proposed in 1989, a researcher named David Strachan observed that children who had older siblings were less likely to develop skin conditions or seasonal allergies. He noticed that over time, average family size had decreased while standard levels of cleanliness had increased in many homes, and he further hypothesized that all of this meant kids had fewer opportunities to get sick. He concluded that young children getting sick was actually a good thing! But why would it be so important for children to get sick?
A child’s developing immune system
Following decades of research about the immune system and how it works, we now know that in order to function properly, the immune system must be “educated” to identify dangerous pathogens such as bacteria and viruses. When babies are born, their immune systems have not been exposed to very many foreign things because they were protected in their mother’s womb. However, children are exposed to all kinds of germs as they grow up, and their immune systems must learn to identify and eliminate things that could make them dangerously ill. While there are many different mechanisms that help properly educate the immune system, one of the key ways that the immune system learns is through the body actually becoming infected with different pathogens; getting sick is part of your body’s education! If the immune system does its job correctly, it will mount a strong and timely response to any dangerous pathogen so that the person will only feel sick for a few days before returning to normal. Most of the time when you feel sick with a fever, cough, or runny nose, this actually means your immune system is doing its job to protect you! The more your immune system learns, the better it is at doing its job, something called immunological memory. But what happens if the immune system is not properly educated?
Evidence supporting the hygiene hypothesis
One outcome of an improperly educated immune system is that instead of attacking foreign pathogens, it may accidentally attack its own “self” proteins or non-harmful allergens. There are a lot of hypotheses and complex mechanisms that could explain why this may be true, but the most simple way to explain the idea is this: if your immune system has little experience fighting off foreign pathogens, it may not know the difference between foreign, self, and non-harmful proteins. In addition, if your immune system is busy fighting off foreign pathogens, it has less time, energy, and resources to attack self or non-harmful proteins. Since originally proposed, many studies have provided evidence supporting the hygiene hypothesis, including the observation that more developed countries (where cleanliness is increased and the occurrence of infection is decreased) tend to have a greater incidence of autoimmune diseases compared to developing countries. There’s also evidence that the overuse of antibiotics in young children increases their likelihood of developing allergies or asthma later on in life. These studies and more have supported the observation that the less frequently children get sick, the more likely they are to develop allergies or autoimmune diseases.
If we stopped washing our hands and stopped cleaning our houses, would it actually eliminate allergies and autoimmune diseases? Sadly, this is not the case. There are a variety of other factors that influence disease, such as genetics, sex, diet, and other environmental triggers. Besides, we all know that washing our hands is a good, sanitary practice. It’s also worth noting that the use of antibiotics has increased life expectancy; in some circumstances, a person’s immune system may need help to successfully eliminate a pathogen. As you can see, the problem is quite complex, and the solution is not simple. What scientific studies have shown us, however, is that getting sick is not always a bad thing, especially in children whose immune systems are still learning to protect them. Admittedly, there are scientists who disagree with the hygiene hypothesis, saying that a properly functioning immune response has more to do with the presence of non-harmful, commensal bacteria than it has to do with exposure to pathogenic bacteria that make us sick. While more studies are needed to further understand these interactions, perhaps the ideas are not mutually exclusive and the solution lies somewhere in the middle. Perhaps we shouldn’t obsess over everything being clean, and we shouldn’t go to extremes to avoid catching the common cold. Instead, we should accept that getting sick every once in a while is totally normal and that there is such a thing as “good” bacteria, and we should allow our immune systems to do what they were designed to do. In the end, maybe the old saying “A little dirt never hurt” has more truth to it than previously appreciated.
