The onslaught of synthetic chemicals has affected people’s immune systems, and microbiomes. Because of this allergies are on the rise, and this enlightening article explains how it all works.
An allergy is an over-zealous immune response by the body to an environmental trigger that is usually something common like food, pollen or pet hair. Whilst many of us experience mild symptoms like itchy eyes or sneezing, for others, allergy can be severe and in the case of anaphylactic shock even life-threatening.
Allergies are on the rise globally, but is it possible that other internal or external factors are heightening our responses? Are we over-burdening our immune systems through our lifestyles and environments?
This article explores these key questions, but first describes what allergies are and the evidence to show they are increasing.
What is an allergy?
An allergy (or hypersensitivity reaction) is our body’s immune response to something that is normally harmless like food, pollen or dust. The immune system protects us through innate (barriers) and acquired (programmed or learned) responses. With an allergy our immune systems are responding to triggers called allergens to disarm it or flush it from our system. We may be affected by itchy skin, sneezing or watery eyes. However, in extreme cases, an individual may experience a life-threatening anaphylactic reaction, and the numbers of people living with allergies as chronic conditions is rising.
An allergy is signified by the release of the antibody immunoglobulin E (IgE) which increases following a cascade of events involving white blood cells T- and B- Cells, Eosinophils, Mast Cells and sometimes Basophils. White blood cells are like the soldiers of our immune system, going out to destroy anything harmful like viruses and bacteria. They communicate through chemicals like cytokines, and antibodies. The following gives a simplified account of what happens during an allergic reaction:
Exposure to environmental allergen à Allergen uptake by antigen-presenting cells and digestion into peptide fragments à Activation of a Th2 cell response à Cytokine release (IL-4, IL-5, IL9, IL13) triggering 1) Eosinophil cells multiply and release contents 2) B cells release IgE, and 3) mast cell degranulation and release of contents.
Mast cells are types of white blood cells that release histamine and other compounds that orchestrate the allergic response. Eosinophils are a different type of white blood cell that also release compounds that cause mucus secretion at sites and smooth muscle contraction. The release of inflammatory compounds like prostaglandins and leukotrienes cause inflammation and worsen the symptoms (14). Allergies are diagnosed through measuring IgE, cytokines and white blood cell biomarkers.
Allergies are on the rise
Allergies manifest in many ways affecting our digestive tract, skin and respiratory systems. They are increasing in prevalence and becoming more severe, with an estimated 44% of the UK adult population suffering from an allergy such as allergic rhinitis, atopic dermatitis, allergic asthma and food allergy (1).
In Europe, it is predicted that 50% of people will be living with allergies by 2025, with pollution thought to add to the problem (2). In China, a population study found asthma to be on the rise and associated with high levels of environmental pollution (12).
In children around the world, eczema, rhinitis and asthma, food allergies are increasing in prevalence, and a global map of food allergy data shows the widespread nature of the problem (17).
Reasons behind allergy rises?
Changes in genes cannot account for the recent and rapid rise in allergy, so what can? For food allergy, egg and milk are most common allergens in children, whereas in adult’s fish and shellfish are more involved. Are food allergies connected to our food systems that have become more homogenous and mass-produced (17)?
What about environmental pollutants? It was recently said that “chemical pollution has passed a safe limit for humanity” (4). Research indicates that air pollution from traffic increases the risk of childhood asthma, and possibly food allergy, eczema and hay fever (2). Co-exposure of a respiratory allergen with diesel exhaust lowers a surfactant protein required for healthy lung function and alters immune regulation (18). Phthalates used as plasticisers in home products like vinyl flooring reduce lung function in allergic patients and boost macrophages and cytokine activity causing an inflammatory response (13).
Pesticides pose a particular risk, and these synthetic chemicals designed to control insects, weeds and fungi pests readily enter our food chain through exposure on farms or in our back gardens, research by Greenpeace in 2015 gives a thorough account (7). In a US cohort study, participants with high levels of urinary dichlorophenols (chemicals used as pesticides and in water chlorination) were more likely to be sensitive to food allergens (11). In agricultural settings, the impact of multiple pesticides on respiratory function in farmers through allergic and non-allergic pathways is even more acute (10). Perhaps most concerning is the potential effects on children’s health. Pesticides are implicated in the rise of many childhood disorders, and for asthma, pesticide exposure can increase the likelihood of being diagnosed with asthma by the age five as well as exacerbating symptoms by causing bronchial constriction (15).
Does nature’s diversity hold the answer?
There are many challenges to address to tackle the rise in allergic disease and underlying connection to environmental pollutants and pesticides. How do we strengthen our body’s resilience or reduce levels of pollution and pesticide use? This article won’t tackle all of this, but one topic of mounting interest is the role of our body’s microbes.
Research shows that pesticides alter the composition of the human gut microbiota where the link to health is well-established (this article goes into more detail about it). More of an unknown is the effect on microbiota metabolism, with the possibility that the bacteria in our gut are transforming the pesticides into more toxic compounds (19). Also, is the microbiota a link between pesticides and the allergic response? In food allergy, individuals have a disrupted microbiome. Certain microbes are important for allowing T cells (a kind of white blood cell) to function effectively, and in this case affects the body’s ability to maintain a tolerance to food (3).Probiotics (live microorganisms that are beneficial when consumed) may offer a solution to restoring microbiota function and remediate against pesticide damage. Lactobacillus promotes detoxification and strengthens host immunity in response to environmental contaminants, although more research in humans is needed (6).
Whilst our inner microbial diversity is important, scientists are also looking at the role of our outer connections too – the biodiversity of the natural world and its importance in creating the resilience needed for life. In one comprehensive review, the authors describe how urban environments disrupt the composition of our skin and airway microbiota. Revegetating and providing green spaces may re-introduce valuable microbiota species into the environment to help restore harmony (8). In Finland, a 10-year Allergy Program successfully reduced the growing prevalence of asthma and allergic disease, alongside less severe symptoms and a 50% decrease in hospital days in those affected. Part of the intervention was improving resilience through boosting contact with the natural environment and eating more healthily, alongside changes to healthcare management (9).
In answer to the second challenge in reducing pollution and pesticide, the discussion is beyond the scope of this article. However, Organic Farming is clearly a means of reducing synthetic pesticide use, and research shows it can restore the lost microbial communities of the soil, including valuable bacterial and fungal groups (16). Therefore, organic methods could also contribute to the idea of resilience through enhancing the microbial diversity in the environment, alongside its other benefits through enhancing biodiversity.
Summary
Allergies are on the rise in children and adults, and there is little doubt that environmental pollutants including pesticides exacerbate illness. As we inhale and ingest these chemicals, our immune systems become overwhelmed and hypersensitive as part of a protective response. As the burden increases, the response can become more severe, and many people are either living with more severe allergy or experience multiple ones. Our microbes are important regulators of our immune system and may worsen the situation through either being disrupted or inadvertently transforming these chemicals into further toxic compounds.
Research is helping us understand how we are impacting our health through damaging our delicate natural ecosystem, and we need to consider the system as a whole in order to address problems like the rising prevalence of allergy.
References
- Allergyuk.org. https://www.allergyuk.org/wp-content/uploads/2022/01/Allergy-UK-Annual-Review-2020-2021.pdf. Published 2021. Accessed February 18, 2022.
- Dantzer J, Keet C. The Influence of Childhood Traffic-Related Air Pollution Exposure on Asthma, Allergy and Sensitization: A Systematic Review and a Meta-analysis of Birth Cohort Studies. Pediatrics. 2015;136(Supplement_3):S233-S234. doi:10.1542/peds.2015-2776w
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- Chemical pollution has passed safe limit for humanity, say scientists. the Guardian. https://www.theguardian.com/environment/2022/jan/18/chemical-pollution-has-passed-safe-limit-for-humanity-say-scientists. Published 2022. Accessed February 18, 2022.
- User S. Allergy. EFA. https://www.efanet.org/inform/patient-evidence/allergy. Published 2022. Accessed February 18, 2022.
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- Astley R, Connor K. Pesticides and our Health – Greenpeace International. Greenpeace International. https://www.greenpeace.org/international/publication/7113/pesticides-and-our-health/. Published 2015. Accessed February 18, 2022.
- Haahtela T, Alenius H, Lehtimäki J et al. Immunological resilience and biodiversity for prevention of allergic diseases and asthma. Allergy. 2021;76(12):3613-3626. doi:10.1111/all.14895
- Haahtela T, Valovirta E, Saarinen K et al. The Finnish Allergy Program 2008-2018: Society-wide proactive program for change of management to mitigate allergy burden. Journal of Allergy and Clinical Immunology. 2021;148(2):319-326.e4. doi:10.1016/j.jaci.2021.03.037
- Hoppin J, Umbach D, Long S et al. Pesticides are Associated with Allergic and Non-Allergic Wheeze among Male Farmers. Environ Health Perspect. 2017;125(4):535-543. doi:10.1289/ehp315
- Jerschow E, McGinn A, de Vos G et al. Dichlorophenol-containing pesticides and allergies: results from the US National Health and Nutrition Examination Survey 2005-2006. Annals of Allergy, Asthma & Immunology. 2012;109(6):420-425. doi:10.1016/j.anai.2012.09.005
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- Maestre-Batlle D, Huff R, Schwartz C et al. Dibutyl Phthalate Augments Allergen-induced Lung Function Decline and Alters Human Airway Immunology. A Randomized Crossover Study. Am J Respir Crit Care Med. 2020;202(5):672-680. doi:10.1164/rccm.201911-2153oc
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- Peltoniemi K, Velmala S, Fritze H, Lemola R, Pennanen T. Long-term impacts of organic and conventional farming on the soil microbiome in boreal arable soil. Eur J Soil Biol. 2021;104:103314. doi:10.1016/j.ejsobi.2021.103314
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