What Changed Our Immune System? A Journey into the Causes of Allergy Spread

SadaNews - In recent years, there has been a noticeable increase in the number of people suffering from allergic diseases, commonly known as allergies. According to estimates from the World Allergy Organization (WAO), allergies affect nearly 20% to 30% of the world's population, marking a rise that warrants attention and an exploration of its causes and related factors.

Allergies are classified as immune diseases and include allergic rhinitis, respiratory asthma, chronic urticaria, eczema, food allergies, insect allergies, drug allergies, eosinophilic esophagitis, and others.

The prevalence of allergies varies based on multiple factors, notably environmental conditions, economic circumstances, geographic distribution, and certain personal practices. Additionally, some types of allergies may be accompanied by other types in the same individual, resulting in suffering from two or more at the same time.

But what recent factors have contributed to the rise of different allergy types among people? What determines their prevalence in specific areas and among certain groups?

Despite the complexity of the causes and the lack of clarity on the precise mechanism that makes some individuals more susceptible than others, studies and research have identified a number of factors as the most prominent candidates behind this rising trend.

Indoor Pollution

Volatile organic compounds (VOCs) - and semi-volatile ones - constitute one of the most significant allergens around us, as they emanate from carpets, textiles, cleaning products, clothing, paint, solvents used in furniture and electronics manufacturing, as well as personal care products like nail polish and hair dyes. The concentration of these substances within modern buildings can be 50 to 100 times higher than outdoor air.

Many upper respiratory tract problems are diagnosed as rhinitis caused by various irritants. A review published by researchers in 2022 in the journal (Frontiers in Immunology) discussed the mechanism by which these compounds provoke allergies, confirming that consistent and intensive exposure to them for extended periods contributes to irritation and chronic inflammation accompanied by disruption of the immune system due to the activation of macrophages and increased levels of inflammatory mediators, exacerbating immune diseases and allergies.

Benzene and toluene are among the most common of these compounds in our daily lives, as they enter the body through the skin, inhalation, or even orally. Other compounds such as esters, amines, ketones, aldehydes, and sulfur- and nitrogen-containing compounds, resulting from cigarette smoke and vehicle exhaust, also join them.

Moreover, mold - a type of fungus - found in homes and buildings, along with smoke leaked from nearby traffic, represents an additional source of these volatile compounds, causing irritation of the nose, eyes, skin, and respiratory tracts.

Additionally, fungi, bacteria, and yeasts inhabit ventilation systems such as air conditioning and heating units and fans. Since we spend about 90% of our time indoors - in offices, schools, homes, and universities - our exposure to these irritants has increased more than in the past, exacerbating allergies of all types over time.

It is worth mentioning that clean places are not exempt from these risks; indeed, a study published by American researchers in 2016 in the journal (Infection Control & Hospital Epidemiology) revealed that the level of germs, including drug-resistant bacteria, in hospital rooms that undergo routine frequent cleaning exceeds that observed in rooms that are only cleaned deeply and thoroughly after each patient leaves.

The Microbiome

The impact of the microbiome residing in our bodies on regulating immune responses is now well-established, and thus any disruption caused by environmental conditions or dietary habits directly affects the quantity and diversity of this microbiome, which in turn influences immunity and allergies.

Many specialists attribute the dysbiosis of the microbiome and the rise of allergic diseases to the reduced levels of our exposure to surrounding microorganisms and those on our bodies, due to communities adopting modern lifestyles that have diminished the transmission of these beneficial organisms among us.

Prominent among these factors are: over-sterilization of drinking water, declining rates of breastfeeding, increasing rates of cesarean births, excessive use of personal disinfectants containing antibacterial agents, and early administration of antibiotics to children. This is further compounded by nearly six decades of widespread antibiotic use, which has contributed to the emergence of resistant bacterial strains.

In this context, American researchers in 2022 indicated a hypothesis linking the spread of allergic diseases to the loss of species and strains of the microbiome within our bodies, alongside reduced environmental exposure to it through water, food, and medication.

With respect to the gut microbiome specifically, researchers from the University of Naples in Italy published a review in 2017 highlighting its role in the development of food allergies, noting that changes in the composition and diversity of beneficial bacteria in the stomach and intestines contribute to damaging the mucosal barrier and weakening its tolerance, leading to food allergies which have saw a significant increase of 8% among children and 10% among adults in industrialized countries.

The researchers confirmed that there are pivotal factors preparing for this allergy at an early age, such as reliance on industrial milk, consuming foods rich in fats and poor in fiber, in addition to the aforementioned factors.

Dysbiosis of the gut microbiome has also been linked to the emergence and exacerbation of other allergic diseases, such as eczema or atopic dermatitis. In 2012, researchers from Linköping University in Sweden conducted an experiment on 40 infants in their first year, aiming to investigate the relationship between microbiome dysbiosis and atopic eczema through the analysis of stool samples.

The results published in the (Journal of Allergy and Clinical Immunology) indicated that reduced quality and quantity of the gut microbiome in the first month of life is associated with an increased risk of developing eczema later on.

In a related study, Danish researchers in 2011 published results from a study tracking the gut microbiome of 411 children and its relation to the risk of developing certain allergic diseases during the first six years of life, revealing that reduced bacterial diversity in the gut during the breastfeeding stage is associated with an increased risk of allergic reactions and allergic rhinitis in later stages.

Not limited to the gut microbiome, research suggests that stable bacteria in the lungs play a key role in regulating immunity and allergic responses, and that an imbalance may contribute to increasing the risk of allergic respiratory diseases such as asthma.

Supporting this, American and European researchers published in 2010 in (PLOS ONE), reported a disruption of the natural bacterial balance of bronchi in patients with allergic respiratory diseases, manifested by dominance of (Proteobacteria) at the expense of (Bacteroidetes), thus supporting the hypothesis linking pulmonary microbiome disruption to increased risk of chronic respiratory diseases such as asthma.

Invasive Dietary Habits and Common Food Types

Modern dietary habits and currently popular food types represent one of the main contributing factors to the rising rates of allergic diseases. In addition to their impact on the microbiome, which plays a central role in regulating immune responses within the stomach and intestines, the effects of nutrients and their metabolic products from gut bacteria extend to the lungs and skin, regulating immune and inflammatory responses therein.

A laboratory experiment on mouse models published in 2022 in the journal (Mucosal Immunity) indicated that consuming foods rich in fermentable dietary fibers contributes to bolstering the skin barrier against allergic diseases by stimulating the production of butyrate, one of the prominent short-chain fatty acids, through the gut microbiome.

The phenomenon of "Western lifestyle" is another notable factor in this context; it has witnessed widespread dissemination after the COVID-19 pandemic in 2020, with a rising dependence on ultra-processed foods, commonly known as "fast food."

In a study published by Chinese researchers in 2024 in the journal (Allergy), it was found that excessive adherence to Western dietary patterns and consumption of ultra-processed foods disrupts the epithelial barriers lining the intestines and skin, thus increasing the risk of chronic inflammatory diseases such as food allergies and others.

It is worth noting that reliance on ultra-processed foods is rapidly accelerating globally; a UN report showed that imports of developed countries from these foods represent 48% of their total food imports, while this proportion is close to 35% in developing countries.

Ultra-processed foods are defined as those ready for immediate consumption, subjected to a series of intensive manufacturing processes, including the addition of flavorings, taste enhancers, and artificial dyes.

Cesarean Births

Many women have recently turned to cesarean births to avoid the changes that may result from natural delivery on the birth canal.

Despite the World Health Organization recommending that cesarean rates should not exceed 15%, this percentage jumped from 6% in 1990 to 21% in 2018, and is expected to continue rising to 30% by 2030, according to a WHO report issued in May 2025.

A systematic review by Chinese researchers published in 2023 linked the rising rates of cesarean deliveries to the spread of allergic diseases, especially allergic rhinitis; it revealed a 19% increased risk of developing it among children born via cesarean, which rises to 82% among those from families with a history of allergy.

These results were reinforced by a comprehensive systematic review published in 2024 in the (Journal of Allergy and Clinical Immunology), which revealed the association of cesarean births with an increased risk of a spectrum of allergic diseases, particularly: eczema, asthma, allergic rhinitis and conjunctivitis, and food allergies.

This is because cesarean delivery deprives the newborn of exposure to the bacteria residing in the natural birth canal, thereby hindering the formation of the gut microbiome community in its early stages, which plays a pivotal role in the maturation of the immune system and preparing it to face diseases, including allergies.

Overuse of Cleaners

A review published in 2024 in the journal (Current Allergy and Asthma Reports) indicated that several phenomena prevalent in contemporary societies have contributed to the rise in rates of allergic diseases.

Notably, the use of dishware after being washed in electric dishwashers leaves traces of cleaning agents on the surfaces of these dishes, which gradually accumulate in the digestive system when used during meals.

Furthermore, over-sterilization with floor and surface cleaners containing sodium sulfate and others raises the rate of inhalation of their volatile particles into the body via the respiratory tract, skin barrier, and ultimately the intestinal barrier.

These factors converge to activate immune cells, escalate rates of oxidative stress, and weaken the immune system, laying the groundwork for triggering allergic reactions.

Not limited to cleaners, the increasing reliance on sterilized and bottled water sources also leads to increased exposure to microplastic particles on one hand, and deprivation of essential minerals lacking in these waters, necessary for supporting the immune system on the other hand, which magnifies the risk of disease.

Pet Ownership

The prevalence of household pets - primarily dogs and cats - has become a widespread global phenomenon, extending to Arab countries, where dominant cultural and religious teachings have historically regulated their ownership and restricted it to specific reasons highlighted clearly in Islamic law. However, successive social, political, and economic changes have led many people to adopt these animals as companions and companions.

Allergies to cats and dogs affect between 10% and 20% of people worldwide and are considered one of the contributing factors to the emergence of various allergic diseases such as asthma, allergic rhinitis, and eczema (atopic dermatitis).

In 2025, Chinese researchers published a study in (Atmosphere) demonstrating that continuous exposure to pets during childhood triples the risk of developing allergies, with this effect being more pronounced in environments with low air pollution levels.

It is noteworthy that the relationship between pet ownership and the risk of allergic diseases remains a subject of debate among proponents and opponents, with conclusive conclusions yet to be reached on this matter.

Antibiotics

British specialists conducted a comparative study published in 2002, indicating that exposure to antibiotics during the first year of life is associated with an increased risk of developing allergic diseases later on, including asthma, eczema, and allergic rhinitis; these antibiotics disrupt the balance of the natural microbiome environment in the body, disturbing the immune system at a critically sensitive stage of growth.

This was confirmed by researchers from China and Singapore in a cross-sectional epidemiological study published in 2019, showing that overuse of antibiotics may be linked to higher rates of allergic diseases, prompting them to call for guidelines ensuring the safe and regulated use of these antibiotics only when absolutely necessary.

These findings were reinforced by a comprehensive Australian study conducted on approximately 800,000 children, revealing that early exposure to antibiotics is associated with an increased risk of allergic diseases later on, with the risk of developing asthma, food allergies, atopic dermatitis (eczema), and allergic rhinitis rising with the increasing number of antibiotic classes received by children, due to the disturbances they cause in the microbiome.

It is noteworthy that global antibiotic usage rates witnessed a significant increase between 2013 and 2016, amounting to a 16.3% rise, reinforcing the hypothesis of a connection between this factor and the spread of allergies.

Source: Al Jazeera