two cupped hands holding dirt with a sprout in the middle

Outdoor play has a number of health benefits beyond exercise. Exposure to animals and dirt at a young age can boost a child’s immunity down the road. 

The basics of immunity

To understand how outdoor play can strengthen the immune system, it is helpful to know how the immune system works.

If a pathogen enters the body, the immune system works to prevent that pathogen from causing illness or injury. There are two types of immune responses – innate and adaptive.

Innate immunity is non-specific, which means that it does not recognize individual molecules but rather repeating patterns that are common to multiple pathogens. Adaptive immunity, on the other hand, involves the detection of specific antigens, or molecules that elicit an immune response.

The adaptive immune response causes certain white blood cells, also known as leukocytes, to remember an antigen once exposed to it. This immunological memory allows for a heightened immune response when the antigen is encountered again.

Immunity involves a number of different types of leukocytes. One type that is involved in adaptive immunity are the T cells. In order for a T cell to function properly, it must bind to the activated form of vitamin D . . .

white clouds and the sun against a blue sky background

. . . Which brings us to the ways in which being outside can benefit the immune system.

Outdoor immune boosts

Many people could tell you that vitamin D is something humans need, and that the sun is a good source of vitamin D. But you probably didn’t know that vitamin D is involved in immunity.

So being in the sun increases your vitamin D absorption. Does the sun have any other positive effects on the immune system?

Probably! In fact, light increases the motility of T cells in vitro. T cell motility is important so that these lymphocytes can reach the site of an infection or invasion. 

Moreover, the sun is not the only component of the outdoors that can heighten immunity.

It is well known that when given the opportunity, many children will play outdoors, coming into contact with various animals, plants, and soils and sometimes even eating these items. Microbes can be transferred to the body via dirty hands or inhalation. Each of those exposures can introduce the immune system to new antigens. 

While the idea of getting dirty on purpose is appalling to most Westerners, it is a common practice in other parts of the world. Indeed, the purposeful consumption of dirt occurs in many places. This act is called geophagy and may seem abnormal in humans, but is prevalent amongst various rodents, birds, and large mammals, including elephants and some primates. 

But why would an animal knowingly eat dirt? 

electron micrograph of human cells dyed green red and blue

A dirty defense

Clays have been used for centuries in food preparation. They have been utilized as spices and to remove toxins. 

However, the most prevalent reason for geophagy across the world is pregnancy. Geophagy is most popular in sub-Saharan Africa.

Dirt and clay contain many microbes. Although scientists are unsure why, when the intestines encounter microbes, tolerance or immunity to the relevant antigen is increased. One of the increased immune responses that results is the heightened production of immunoglobulin A (IgA).

IgA is a molecule that is transferred from mother to child through the placenta and breastmilk. So by eating dirt regularly, a mother may boost her baby’s immunity.

Prenatal exposures to various antigens contribute to a child’s immune system. The microbes a person encounters during the first few years of life are also significant in this development. Possible sources of diverse antigens in the early years include breastmilk, antibiotics, and the environment. 

You might be wondering why it is so important to build up the immune system from a young age. Can’t we just increase our immunity as we age?

While it’s possible to heighten your immunity throughout life, and this does happen, the early formation (or a lack of formation) of the immune system is very influential on the diseases one develops down the road.

Severe or chronic inflammation in utero and during early childhood increases the likelihood of later being diagnosed with a number of neurodevelopmental and psychiatric disorders.

It has been found that when a young child visits a farm, they may be less likely to get asthma. In addition, maternal exposure to farms during pregnancy decreases the likelihood of childhood allergies.

This is not to say a person should eat dirt on purpose, though. Eating dirt can expose you or a growing fetus to a number of health risks, like feces, parasites, and harmful microbes, as well as high amounts of dangerous chemicals, especially lead. Building up a healthy microbiome and immune system is important, but so is avoiding the chance of illness.

To summarize, it is arguably a good thing that your toddler enjoys playing with dirt. Just make sure they aren’t ingesting much dirt or getting it on their face. While you might not appreciate it in the moment, your child’s immune system will certainly reap the benefits!

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Tom · July 4, 2020 at 5:57 pm

What age should we be letting our little one ‘get dirty’?

    Delaney Lynn · July 6, 2020 at 3:57 pm

    Good question! According to the article linked below, the immune system matures as an infant ages, so by the time a child is toddler their innate and adaptive immune systems should work pretty well. However, infants get immunity from many diseases from their mothers through breastmilk, whereas young children don’t have this benefit, and are therefore more susceptible to getting diseases. They’re better at fighting them off, though, because their immune systems have matured.

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