World Allergy Day | Contemporary “allergy crisis”: Why are our bodies becoming more and more sensitive?

Today is World Allergy Day. Every year on July 8, the world aims to raise awareness and prevention of allergic diseases. In recent years, the incidence of allergic diseases has increased significantly, affecting a large number of people around the world.

Today, on World Allergy Day, let’s explore a growing global health issue: Why are allergic diseases showing an alarming growth trend around the world? This article will briefly analyze the complex reasons behind this phenomenon based on some of the latest scientific research results.

1. The global spread of allergy symptoms

According to a Global Burden of Disease study published in The Lancet in 2020, the prevalence of allergic rhinitis and asthma has increased significantly worldwide over the past 30 years [1]. This trend is particularly evident among children and young people, which has attracted widespread attention in the medical community. Studies have shown that in some countries, up to 40% of the population is troubled by allergic diseases, a figure far exceeding that of decades ago.

2. The impact of modern lifestyle

1. New Hygiene Hypothesis Explanation

The traditional hygiene hypothesis holds that an overly clean environment leads to a lack of "training" of the immune system, thereby increasing the risk of allergies. However, a review article published in the New England Journal of Medicine in 2019 proposed a new view [2]. The researchers pointed out that it is not just the level of cleanliness, but the reduction in microbial diversity in the environment that is the key factor. The urbanization process has led to a decrease in the types of microorganisms that people are exposed to, which may be an important cause of immune system disorders. For example, studies have found that children who grow up on farms have more than 50% lower risk of allergic diseases than urban children.

2. Changes in diet

A study published in the journal Nature in 2021 revealed that the globalization of Western dietary patterns may be associated with the increase in allergic diseases [3]. The intake of high-fat, high-sugar, and highly processed foods changes the composition of the intestinal flora, which in turn affects the function of the immune system. Studies have shown that people who follow traditional dietary patterns such as the Mediterranean diet have a significantly lower incidence of allergic diseases than those who mainly consume Western fast food.

3. The role of environmental factors

A. The impact of air pollution

A large-scale study published in the European Respiratory Journal in 2019 revealed the significant impact of air pollution on the incidence of childhood asthma [4]. The study found that across Europe, more than 670,000 new cases of childhood asthma each year can be attributed to air pollution. Among them, nitrogen oxides (NO2) are the main causative factor, accounting for 15% of cases. The study also pointed out that if all study cities can reduce NO2 levels to below 40 μg/m3 recommended by the WHO, nearly 2,000 cases of childhood asthma can be prevented each year. This study highlights the importance of improving air quality in reducing the incidence of allergic diseases in children.

B. Climate change

A 2023 review article in the American Journal of Allergy, Asthma & Immunology pointed out that rising temperatures and increased carbon dioxide concentrations caused by climate change have extended the pollen season and increased pollen production, thereby exacerbating allergy symptoms. [5] For example, in North America, the ragweed pollen season is nearly four weeks longer than it was 20 years ago.

C. Gene-environment interactions

A study published in Nature Genetics in 2021 emphasized that the increase in allergic diseases may be the result of a complex interaction between genetic and environmental factors [6]. Certain gene variants may increase the risk of allergies under certain environmental conditions. For example, individuals with a specific variant of the STAT6 gene have a significantly increased risk of developing asthma when exposed to indoor mold.

D. Changes in the microbiome and allergies

The latest cutting-edge research focuses on the role of the human microbiome. A study published in Science magazine in 2022 showed that an imbalance in the early intestinal and skin microbiomes may be one of the key factors leading to an increase in allergic diseases [7]. The study found that infants with low intestinal microbial diversity within 3 months of birth had a 3 times higher risk of developing food allergies at the age of 3.

Although the increase in allergic diseases is worrying, advances in scientific research also bring hope. Understanding the reasons for the increase in allergies can help us develop more effective prevention and treatment strategies. For example:

Ⅰ. Dietary intervention: Encourage a varied, fiber-rich healthy diet to promote the diversity of intestinal microorganisms.

Ⅱ. Environmental exposure: Moderately increase children’s opportunities to be exposed to the natural environment, such as outdoor activities and contact with farm animals.

III. Improve air quality: Reduce air pollution through policy and technological innovation.

IV. Personalized prevention: Develop targeted allergy prevention strategies based on individual genetic characteristics.

V. Microbiome intervention: Develop novel therapies such as probiotics or microbiome transplantation to modulate immune system function.

Finally, the increase in allergic diseases is a complex problem caused by multiple factors. It reflects the changes in our modern lifestyle and environment. As individuals, we can reduce the risk of allergies by maintaining healthy living habits; from a social perspective, we need to work together to create a living environment that is healthier and friendlier to nature.

On this World Allergy Day, we can work together to focus on this important health issue and work towards a "less allergic" future. By understanding the causes of the increase in allergic diseases, we can not only better prevent and manage these diseases, but also provide a scientific basis for building a healthier and more balanced living environment. Together, we can create a world with fewer allergies and a healthier world.

References:

[1] GBD 2019 Diseases and Injuries Collaborators. Global burden of 369 diseases and injuries in 204 countries and territories, 1990–2019: a systematic analysis for the Global Burden of Disease Study 2019. The Lancet, 2020.

[2] Lambrecht, BN, & Hammad, H. The immunology of the allergy epidemic and the hygiene hypothesis. Nature Immunology, 2019.

[3] Wesemann, DR, & Nagler, CR The microbiome, timing, and barrier function in the context of allergic disease. Immunity, 2021.

[4] Khreis, H., Cirach, M., Mueller, N., de Hoogh, K., Hoek, G., Nieuwenhuijsen, MJ, & Rojas-Rueda, D. Outdoor air pollution and the burden of childhood asthma across Europe. European Respiratory Journal, 54(4), 1802194, 2019.

[5] Ziska, LH, et al. Temperature-related changes in airborne allergenic pollen abundance and seasonality across the northern hemisphere: a retrospective data analysis. The Lancet Planetary Health, 2023.

[6] Muraro, A., et al. Precision medicine in allergic disease–food allergy, drug allergy, and anaphylaxis-PRACTALL document of the European Academy of Allergy and Clinical Immunology and the American Academy of Allergy, Asthma and Immunology. Allergy, 2021.

[7] Stokholm, J., et al. Maturation of the gut microbiome and risk of asthma in childhood. Nature Communications, 2022.