‘Does playing in the dirt help kids develop a strong immune system?‘.
Rather than playing in dirt per se, growing up in ‘natural’ environments helps kids develop a balanced immune response while strength is an unhelpful gauge of immune system function. This answer clarifies
- How exposure to dirt became associated with immune system functioning.
- Why rather than strength, whether or not an immune response is orderly/well-controlled is a more appropriate gauge for assessing immune response outcome.
- Why it’s more accurate to consider ‘playing in the dirt’ not literally but rather as a metaphor for a more consciously ‘natural’ living.
How did the notion of playing in the dirt get linked to immune system function? Steadily through the 20th century til date, epidemiologists noticed a sharp uptick in rates of a variety of chronic inflammatory disorders such as allergies and autoimmunities in, meaning throughout Western Europe, North America and Australia.
Such abrupt onset and spread of non-infectious diseases within a mere generation or two made purely genetic causes such as mutations less likely. The timeline instead fingered as-yet unidentified environmental factors. What could they be?
In 1989, the epidemiologist David Strachan observed a tendency for younger siblings within large families to be much less predisposed to allergies such as hay fever and eczema. Specifically, the record suggested protection for younger siblings who developed a series of childhood infections (). This implied a role for childhood infections in resistance to allergies.
Around the same time, multiple studies started correlating resistance to allergy and autoimmunity with childhood exposure to farms or farm living (). The link between farm living and protection against chronic inflammatory disorders brought to focus environmental factors associated with farms, obviously dirt and plenty of it as well as poop and plenty of it (see below from ).
The link with poop coincided with the discovery of the importance ofin human physiology, which thus expanded the ambit from infections to microbes in general.
In recent decades such observations thus helped narrow down environmental factors to microbiota. Specifically, ‘Western’ living typically entails,
- Few people in these countries live on farms.
- Indoor sanitation and piped chlorinated drinking water are standard.
- Exposure to antibiotics and a wide variety of antiseptic agents (cleaners, wipes, lotions) is widespread and frequent.
- Hospitalized births are standard and increasingly those births are C-section.
Thus, excessive hygiene, especially in childhood, leads to an abrupt and sharp decline in natural exposure to all sorts of microbes. The gist of such observations became codified as the, that ‘Western’ lifestyle increasingly automatically undermines natural exposure to microbes. This in turn fundamentally alters how the immune system gets ‘trained’ during formative years and thus increases the risk for inflammatory disorders. How exactly this happens remains the focus of intense research.
What is a strong immune system? Strength of the immune system is inadequate to the task of properly assessing immune function since someone with autoimmunity has a demonstrably strong immune system. Similarly, someone with allergy makes demonstrably strong immune responses toperceived as innocuous by others. Rather than strength, disorder or dysregulation sets apart immune system function in inflammatory disorders. Thus, it’s more accurate and appropriate to focus on how the immune system functions, orderly or disorderly, rather than its strength.
Why playing in the dirt is better considered a metaphor for more natural living. Since time immemorial, humans have had interactions with the natural world which included children playing in the dirt. As outlined above, thecreated a schism by making possible living that represents a drastic difference in kind from that past. However, it did so at the expense of the environment with clean air, water and soil its prominent casualties. Industrialization ended up desecrating and polluting vast tracts of the land all around us, especially urban lands. In many places, the land has become polluted with toxic products of industrial runoff, lead being a case in point. As a 2015 report notes (see below from ),
‘Urban soil has become severely lead contaminated, especially in inner cities (Filippelli and Laidlaw 2009; Mielke et al. 2013).’
Thus, when it comes to playing in the dirt, discretion becomes the better part of valor with parents and caregivers taking care to ensure the ‘dirt’ children play in is really wholesome dirt and not soil that in the past was subjected to industrial activity. Deliberately choosing several other options and activities would also help ensure children develop the ability to make balanced immune responses.
- Reducing exposure to unnecessary antibiotics and antiseptic agents.
- Choosing C-section only when medically necessary and not as an elective.
- Frequent exposures to farm environments, for example frequently visiting petting zoos and keeping pets at home.
- Spend more time outdoors in natural environments, more pristine the better, national parks being case in point.
- Feeding a diet largely composed of fruits and vegetables with plenty of natural fibers while avoiding processed foods as much as possible would help children develop and sustain the type of diverse microbiota associated with health.
1. Strachan DP (1989) Hay fever, hygiene, and household size. BMJ 299, 1259–1260.
2. Kabesch, Michael, and Roger P. Lauener. “Why Old McDonald had a farm but no allergies: genes, environments, and the hygiene hypothesis.” Journal of leukocyte biology 75.3 (2004): 383-387.
3. Mielke, Howard W. “Soils and Health: Closing the Soil Knowledge Gap.” Soil Horizons 56.4 (2015).