Exposing kids to germs may seem like a simple way to prevent allergies, but there is more nuance to the link between the two. Allergies and different atopic diseases are connected with genetic predisposition. However, despite this genetic link, there has been a noticeable and consistent rise in these conditions over the past few decades. This rapid increase cannot solely be attributed to genetic shifts, as such changes typically occur gradually. It suggests that environmental and lifestyle factors significantly influence the development and prevention of allergies.
The epidemiologist, Dr Strachan first introduced the “Hygiene hypothesis” stating the inverse relationship between family size and the occurrence of atopic diseases. He proposed that a lower incidence of infections during early childhood transmitted by older siblings could be the cause of the rise in allergic diseases. The media has focused on a hypothesis that suggests a decrease in key exposure due to smaller family sizes, improved household amenities, and higher personal cleanliness standards, resulting in cleaner homes.
In the following paragraphs, we will talk about the relationship between family size, food-borne diseases and allergies.
The rise in atopic disease
The industrialized world had a significant surge in allergic asthma and other atopic illnesses between 1960 and 1970, with further increases in the 1980s and 1990s. For example, asthma prevalence has grown by around 1% every year since 1980.
The reunification of Germany shed light on how lifestyle affects atopic illness in highly homogeneous populations. Scientists found a considerable rise in hay fever and atopic sensitization among youngsters in former East Germany from 1991-1992 to 1995-1996.
Previous research has found lower rates of ‘Western living’ in East Germany compared to West Germany, raising concerns about its impact on children.
Family size and allergies
Numerous studies have revealed links between atopic disease and family structure. However, these links are less consistent for specific atopic diseases, birth order, sibling size, and gender. Studies utilizing hay fever, skin prick positivity, and specific IgE levels as indicators revealed an inverse relationship between atopy and family size. Scientists found that having three or more older siblings can protect children aged 3-5 years against asthma, defined as coughing or wheezing during the past 12 months (1).
Although these parameters are linked to the occurrence of atopic illness, epidemiological studies do not explain the nature of this association.
Close Contact
Childhood bedroom sharing, which is more common in big families, was found to reduce the likelihood of developing atopic illness later in life. This supports the hygiene concept by increasing the likelihood of illness or microbial exposure (2). At the age of two, children who had greater exposure to other children at home or daycare were more likely to experience frequent wheezing; however, from the ages of six to thirteen, this risk was reduced.
Farm and other rural exposure
For a long time, people have been curious about the differences between those who live in rural areas and towns. According to recent research, the farm alone—rather than the entire rural area—is the component that has a preventive effect on atopy. For instance, compared to other rural residents, children of farmers had a lower prevalence of hay fever (3).
Food-borne and gastrointestinal disease
Bacterial and viral infections
The most convincing proof of a negative correlation between atopy and exposure to a particular disease comes from the Hepatitis A virus (HAV), which is linked to low socioeconomic position and big family sizes. Research conducted as a retrospective case-control study among male Air Force cadets in Italy discovered that cadets with atopy had significantly lower serum levels of antibodies to Helicobacter pylori, Toxoplasma gondii, and HAV than nonatopic controls.
However, the study did not evaluate the independent effects of specific infections. According to the researchers’ findings, a Westernized, semi-sterile diet and good hygiene may promote atopy by altering the general pattern of commensals and pathogens that stimulate the gut-associated lymphoid tissue. Additionally, early exposure to microbes through orofaecal and food-borne routes protects against respiratory allergies (4).
Gut flora
The gut’s bacterial flora is one possible mechanism by which microbial exposure protects against atopy. According to one research children with allergies have a different intestinal flora than children without allergies. This is because the intestinal flora of allergic children has a higher prevalence of aerobic bacteria, coliforms, and Staphylococcus aureus. The gut flora of the children who were not allergic showed a higher frequency of Lactobacilli and Bifidobacteria spp.
Atopy and other immune-related conditions, including the response to infection, may benefit from “probiotics”—preparations that typically contain lactic acid bacteria, such as Lactobacillus or Bifidobacterium—that help preserve intestinal mucosal integrity and prime or maintain normal gut flora. Compared to other types of atopic disorders, probiotics may offer greater protection against eczema. Probiotics may help shield children against respiratory and diarrheal illnesses while they are in high-risk environments, such as daycare centres, according to recent research (5).
Intestinal parasites
Numerous investigations have revealed that intestinal helminth infestation, especially a severe and long-lasting infection, may prevent atopy. In contrast to the urban population, self-reported wheeze was shown to be lower in Ethiopia’s rural subsistence regions. A follow-up research in the same community revealed that high levels of parasite infection, namely hookworm, reduced asthma symptoms in atopic persons. These results are first unexpected because helminth infections induce a Th2 bias.
However, they were initially explained by a “blocking” mechanism in which polyclonal IgE antibodies overloaded the accessible cellular IgE receptors. However, helminth infections also have an immunosuppressive impact. More recent theories on the protective effect suggest that this is due to the development of a robust immune system and anti-inflammatory properties that reduce symptoms in those who would otherwise be allergic. A more nuanced picture is painted by other data, which show that SPT reactivity is suppressed but not asthma or allergic rhinitis (6).
This evaluation provides substantial support for activities aimed at improving hygiene practice, even though it indicates that the hypothesis of hygiene and hygiene practice has not been proven. ‘Targeted hygiene,’ which focuses on selective hygiene intervention when and where infection risks are highest, makes sense on its own merits because it aims to maximize protection against the harmful effects of infectious diseases while maintaining the beneficial effects that microbes may have on our human and natural environment, regardless of the reality surrounding atopy and microbial exposure.
