Itchy eyes, stuffy nose and sneezing are all common during ‘allergy season.’ Yet many allergies, particularly food allergies, are not just an inconvenience, they can be fatal — and they are on the rise.
6.1% of children under the age of 18 reported having food allergies between 2015 and 2017 in the United States. Between 1997 and 1999, this number was only 3.4%. Over time, the prevalence of childhood and adolescent allergies has increased substantially. However, even with this increase, the origin of allergies still remains largely unknown.
Allergic reactions occur when the body’s immune system incorrectly identifies a food molecule as harmful and begins to attack it. At this point, the cells release histamines — chemicals that work to rid the body of harmful pathogens — and other compounds that can cause various symptoms such as sneezing, wheezing, vomiting and hives. In more extreme cases, the airways constrict and blood pressure decreases, resulting in a loss of consciousness and anaphylaxis — which is when the body goes into shock. An allergic reaction can be life-threatening if the individual does not receive medical treatment immediately.
Allergy research is a fairly novel field: the term itself was first coined in 1906. Only in the latter part of the 20th century did researchers begin to discover the cells and mechanisms that drove food allergies: predominantly mast cells, a central component of the body’s immune system, and antibodies known as IgE. These antibodies travel to mast cells and cause the release of histamines, which in turn triggers an allergic reaction. Scientists have continued to study the complex causes of food allergies, resulting in many hypotheses being formed.
One such hypothesis is the “Hygiene Hypothesis,” which suggests that the “extreme cleanliness” of the developed world actually hinders the developing immune system of an infant, as they are exposed to less germs. This decreased exposure may cause their immune system to incorrectly identify food molecules as pathogens, which in turn leads to symptoms such as allergic reactions and asthma. However, scientists are still studying the extent to which this cleanliness plays a role in the development of allergies.
Other studies have shown that mothers can pass on allergies to their children, since maternal antibodies can cross the placenta. The mother’s IgE antibodies can bind to the cells of the fetus, causing them to also develop allergic reactions to the same allergens, or substances that cause reactions, after birth.
Another clinical study done by the Mayo Clinic finds that antibiotics may also play a role in the development of allergies: children receiving multiple antibiotic treatments under the age of two are more likely to have conditions such as allergies, asthma, ADHD and eczema. Researchers believe that this may be attributed to the “disruption of the bacteria in a baby’s gut,” since antibiotics kill both ‘good’ and ‘bad’ bacteria, leaving the digestive system defenseless against harmful pathogens.
New research also suggests that allergic diseases may be linked to different genes based on factors such as ethnicity and environmental conditions. Although all result in allergic reactions, differences in DNA sequences across various ethnic populations may result in varying levels of reaction severity. In addition, environmental exposures such as smoking, air pollution and stress can cause modifications in genes, leading to an evolution of allergic reactions or asthma.
To date, there is no definitive answer as to what causes allergies. The true origin may in fact be a mix of all these theories, or a new theory entirely. Further studies are needed to determine whether these factors are associated with allergies, or in fact cause them to develop. However, understanding the components that spark allergic reactions is instrumental in treating and preventing a condition that is becoming much more wide-spread.