What is the cause of the increasing prevalence of allergic reactions (hypersensitivity reactions)?

From the Guidelines

The rise in allergies worldwide is primarily due to changes in our environment and lifestyle, with factors such as the "hygiene hypothesis", climate change, air pollution, and dietary changes all contributing to the increasing prevalence of allergies. According to the study by 1, food allergy affects up to 8% to 11% of the US population, and the rates of food allergies in US children increased by about 50% between 1997 and 2011. The "hygiene hypothesis" suggests that our overly clean environments prevent our immune systems from learning to distinguish between harmful and harmless substances, leading to an increased risk of developing allergies 1. Additionally, climate change has extended pollen seasons and increased pollen potency, while air pollution can make allergens more aggressive and damage respiratory tissues.

Some key factors that contribute to the rise in allergies include:

• Changes in diet, including increased consumption of processed foods and decreased consumption of fresh fruits and vegetables
• Increased use of antibiotics, especially in early childhood, which can disrupt gut microbiome development and immune regulation 1
• Genetic factors, such as having allergic parents, which can increase the risk of developing allergies 1
• Reduced exposure to diverse microbes during childhood, which can prevent the immune system from developing properly 1

To reduce allergy risk, especially in children, consider:

• Moderate exposure to pets and outdoor environments
• Breastfeeding when possible
• Introducing diverse foods early
• Limiting unnecessary antibiotic use
• Maintaining good indoor air quality. As stated in the study by 1, food-induced anaphylaxis can result in significant economic burden, including prehospital emergency care, ED visits, hospitalizations, and even death, highlighting the importance of taking steps to reduce allergy risk.

From the Research

Allergy Prevalence

• The prevalence of allergies has been increasing globally over the last few decades, with changes in environment and lifestyle being major contributing factors 2.
• This increase is particularly notable in westernized countries, where the prevalence of food allergy has been rising, especially among children 3.
• The rise in allergy prevalence is not limited to high-income countries, as low and middle-income countries are also experiencing an increase in allergic diseases 4.

Environmental Factors

• Environmental factors, such as air pollution, climate, and exposure to allergens, play a significant role in the development and exacerbation of allergic diseases 5.
• Airborne allergens like dust mites, pollens, fungi, and animal dander are among the most extensively studied environmental factors influencing allergy 5.
• Other environmental factors, including infections and exposure to chemicals, can also contribute to the development and course of allergic diseases 5.

Lifestyle Factors

• Lifestyle factors, such as diet and socioeconomic status, can also impact the prevalence of allergies 3, 4.
• The "hygiene hypothesis" and "biodiversity hypothesis" suggest that a lack of exposure to certain microorganisms and a decrease in biodiversity may contribute to the increasing prevalence of allergies 4.
• Further research is needed to fully understand the relationship between lifestyle factors and allergy prevalence 2, 4.

Demographic Factors

• Allergic diseases are more common in childhood than in adulthood, and affected children contribute more to the rise in allergic disease prevalence than affected adults 4.
• The prevalence of allergies can vary depending on ethnicity and geographic location, with certain populations being more or less susceptible to specific allergies 3, 4.