Currently, we have a good understanding of what occurs during an allergic or autoimmune response. Usually, the immune system will identify and destroy a foreign substance in the body that is considered harmful. However, in allergy or autoimmunity, the immune response becomes exaggerated or hypervigilant. In this case, the immune system will react to something that enters the body, which is either benign or is, in fact, a part of the body.
The Complex Causes Behind Allergies and Autoimmunity
Such reactions can be a nuisance in the case of seasonal allergies, debilitating in the case of rheumatoid arthritis, or even life threatening in the case of asthma. Nevertheless, the incidence of allergies and autoimmune disease continues to increase in Western society and now research on how it develops garners much attention. There are many proposals on what causes allergy, but when surveying all of them, it becomes clear that allergy and autoimmune disease result from a confluence of factors. Research demonstrates that many factors serve to influence the risk of allergy development in children, including heredity, maternal exposures, breastfeeding, hygiene, previous infections and air quality.
Studies show that children living in smaller families and in higher hygienic conditions have a significantly increased incidence of allergies compared to those in larger families or those living on farms
Genetics, Epigenetics and Environment: Unraveling the Complex Causes of Allergies
Though genes play a significant role in determining our physical traits, they are not solely responsible for conferring them. With the emergence of epigenetics, we now know that the environment (nutrition, lifestyle, & metabolism) plays a significant role in gene variability and expression. Studying the genetic link to allergies, such as asthma or eczema, poses significant challenges. These genes can be found on seven different chromosomes and at multiple sites, so the association between genes and the incidence of allergies does not follow a single cause, single entity dynamic.
Recent studies of twins show mixed results. In one large scale study where one twin showed symptoms of hay fever or asthma, there was approximately a 60% chance the other twin would have such symptoms. Still, environmental factors can cause a 40% variability. In another study of twins, less correlation was found when comparing skin prick tests. Family history is the clinical method most commonly used to assess the genetic role of allergy development.
Large scale studies have shown a two to four times increase in risk for developing seasonal allergies and asthma where there is a family history compared to those who don’t have a family history of such events. When studying genetics by looking at commonalities between twins or other family members, we must also acknowledge that there are environmental factors that are often passed down in families along with our genes. The effect of diet and lifestyle, therefore, must also be considered as an essential influence on genetic expression.
How Pregnancy Nutrition Influences Infant Allergy Risk
Mom’s eating habits during pregnancy may alter infant allergies. In a study of 769 Japanese mothers and child pairs, researchers found that those with a higher intake of green and yellow vegetables decreased the incidence of eczema in offspring and that increased intake of fish oils reduced the incidence of wheezing. We also know that the fetus can produce an immune response when the mother is exposed to allergens as early as the eighth week of pregnancy.
Allergic substances that are ingested or inhaled by the mother can pass through the placenta and are either inhaled, ingested, or absorbed through fetal skin. A number of studies show that allergens found in amniotic fluid at week sixteen can remain present in fetal circulation at term and during that time, the fetus is capable of building an immune response to these maternal allergens. Also, follow up studies of in utero sensitization demonstrate a higher likelihood of having positive skin prick tests.
The Role of Maternal Diet and Breastfeeding in Preventing Childhood Allergies
Current research indicates that for pregnant women, avoiding allergens and adhering to meals rich in diverse vegetables while including some omega-3 fats lowers the incidence of childhood allergies such as asthma and eczema. Also, the beneficial relationship between breastfeeding and the development of allergy is practically undisputed. Hundreds of studies point out the benefits that breastfeeding has with respect to the emergence of allergy symptoms in childhood.
Breastfeeding children will result in fewer incidences of cow milk allergy, reduced asthma risk, and fewer incidences of allergic skin reactions in childhood. It is now universally recognized that there is no commercial formula that can equal breast milk since breast milk has an individualized composition of macronutrients. In addition to the appropriate amounts of carbohydrates, protein and fat, breast milk also provides vitamins, minerals, digestive enzymes and hormones all of the things that a growing infant will require. Breast milk also contains antibodies and lymphocytes from the mother that help the baby’s immune system.
Factors | Key Findings |
|---|---|
Heredity | Family history increases allergy risk 2- 4x; environmental factors modulate genetic expression |
Maternal Exposures | Maternal intake of vegetables/fish oil lowers eczema and wheezing; the fetus may be sensitized in utero |
Breastfeeding | Breastfeeding reduces the risk of asthma, eczema, and food allergies; provides immune protection |
Hygiene | High hygiene is linked to more allergies; less microbial exposure in early life is linked to immune hyperreactivity |
Air Quality | Pollution and tobacco smoke exposure increase asthma/allergy prevalence, especially in urban areas |
The Link Between Hygiene, Family Size and Allergy Development
The hygiene hypothesis is gaining a great deal of traction. According to this idea, the presence of hygienic conditions and fewer infections results in an under-stimulated immune system, which leads to the signs of hypervigilant immunity such as asthma, hayfever and eczema. Studies show that children living in smaller families and higher hygienic conditions have a significantly increased incidence of allergies compared to those in larger families or those living on farms.
Children in high hygiene environments experience fewer infections, are exposed to fewer infectious agents and show less diversity in bowel probiotics on microscopic evaluation. After assessing several studies, a recent review article stated that an increased exposure to infectious agents in the early years of life is associated with a decreased incidence of allergy and autoimmune disease later on.
Exposure to environmental pollutants and tobacco smoke in early life has been tied to the development of conditions such as asthma, hay fever and eczema
The Impact of Air Pollution and Tobacco Smoke on Childhood Allergies
The largest investigation conducted on a group of people with similar genes but different exposures to airborne pollutants was during the reunification of Germany. This provided an excellent opportunity to assess how allergy development is influenced by sulfur dioxide exposure in East Germany versus the exposure to nitrogen dioxide in West Germany. When compared, the children in East Germany had significantly less prevalence of asthma, bronchial hyperresponsiveness and hay fever, thereby demonstrating that poor ambient air quality results in more allergic disease in children.
We also see this association with tobacco smoke and it is likely to start in utero. More than half of infants born to mothers with maternal cigarette exposure in the womb will develop asthma, eczema, or hay fever compared to one third of those without such exposure. Also, children exposed to environmental tobacco smoke have an increased incidence of asthma symptoms such as wheezing. The effects of air pollution on airway disease and allergic symptoms have become a topic of concern since the prevalence of ‘smog’ days in urban centers continues to rise.
How Air Pollution and Early Exposures Drive Allergic Diseases
The effects of smog on airway health were clearly demonstrated after an inversion of air pressures in the 1970s trapped smog over the cities of the eastern United States coast. During this time, hospitals experienced a dramatic increase in hospital admissions and deaths due to asthma and allergic reactions in the airways. Moreover, to this day we see a rise in allergic respiratory disease in urban centers compared to rural areas.
It is in the urban centers where we encounter far higher concentrations of airway pollution from industry and vehicle emissions. Exposure to environmental pollutants and tobacco smoke in early life has been tied to the development of conditions such as asthma, hay fever and eczema.
There are many factors that influence the emergence of allergies early in life. Current research finds that the development of allergic conditions such as asthma, eczema and hay fever is linked to genetics, maternal exposures, breastfeeding, hygiene, previous infections, and air quality. Having a more thorough understanding of the process by which these allergies arise may help to stem their increasing prevalence in industrialized nations.
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Frequently Asked Questions (FAQs)
1. Can allergies be inherited from parents?
Yes, family history significantly increases allergy risk. Studies show children with a parent or sibling who has allergies are 2 to 4 times more likely to develop them. However, environmental factors like diet and pollution also shape how genes are expressed.
2. How does a mother’s diet during pregnancy affect a child’s allergy risk?
Maternal nutrition plays a critical role. Diets rich in green/yellow vegetables and omega-3 fats (e.g., fish oils) during pregnancy are linked to reduced eczema and wheezing in children. Conversely, processed foods and allergens ingested by the mother may sensitize the fetus.
3. Does breastfeeding help prevent childhood allergies?
Yes. Breastfeeding is strongly associated with lower rates of asthma, eczema, and food allergies. Breast milk provides immune boosting antibodies, hormones and nutrients that commercial formulas cannot replicate.
4. Is the “hygiene hypothesis” valid?
Research supports the idea that limited early-life exposure to microbes (due to excessive hygiene) can lead to an overactive immune system, increasing allergy risk. Children in rural areas or larger families often have fewer allergies due to diverse microbial exposure.
5. How does air pollution contribute to allergies?
Exposure to pollutants like PM2.5, NO2 and tobacco smoke in early childhood is linked to higher asthma and allergy rates. Urban areas with high traffic emissions see more allergic respiratory diseases compared to rural regions.
Summary: Understanding Allergy Development
Allergies arise from a complex interplay of genetics, environment and lifestyle:
- Genetics: Family history increases risk, but epigenetic factors (e.g., diet, pollution) modulate gene expression.
- Maternal Influences: Prenatal nutrition and allergen exposure can sensitize the fetus, while breastfeeding provides critical immune protection.
- Environmental Triggers: Urban air pollution, tobacco smoke and overly hygienic environments disrupt immune tolerance, raising allergy risk.
- Hygiene Hypothesis: Limited microbial exposure in early life may lead to hypervigilant immune responses, favoring allergies.
By addressing modifiable factors such as diet, pollution avoidance and balanced microbial exposure, parents and individuals can reduce allergy risk.
