What Causes Allergies?
The prevalence of allergies is on the rise, but why do some people suffer allergic reactions while others don’t? If you were lucky enough to be an allergy-free kid, could you still develop allergies as an adult?
Almost 8% of adults and 9% of children in the U.S. suffer from nasal allergies or hay fever, and the symptoms result in over 11 million visits to the doctor annually. Three million people in the U.S. further report an allergy to peanuts, or tree nuts or both, including 8% of children, according to the American Academy of Allergy Asthma and Immunology.
The prevalence of allergies also appears to have increased over the last 50 years and shows no signs of slowing down. As the House Call Doctor explained, allergy symptoms occur when our immune system mistakes a normal substance, like pollen or a nut, for an intruder, and wages war against it through the release of antibodies. But why does this response happen in some people and not others? Why are allergies becoming more and more common? If you were lucky enough to be an allergy-free kid, could you still develop allergies as an adult?
Genetics and Our Environment
Scientists are not entirely sure why some people suffer from allergies while others live allergy-free, but studies show that genetics and environment are both important factors.
Studies of twins for which at least one twin is allergic to peanuts have found that, in the case of fraternal twins, the other twin has a 7% chance of also having the allergy. Among identical twins, however, both twins were allergic in 64% of cases. Thus, our genetics clearly influence whether or not we will have an allergy.
However, the strength of the connection between genetics and allergies is still up for debate. In a Canadian study of over 900 siblings of kids with peanut allergies, for example, only 1.7% of siblings were also allergic. We also appear to inherit the tendency to have allergies, but not a specific allergy. In other words, having a parent who is allergic to nuts does not mean that you will necessarily also be allergic to nuts, but it does increase your chances of having any allergy at all.
Our environment must also factor into determining whether or not we will ultimately be allergic. A recent study has shown that the rates of allergies and asthma are lower for those living on farms, possibly due to exposure to a specific molecule found in cow manure.
Ultimately, our environment determines whether or not we will be exposed to a particular allergen, a requirement for developing an allergy. However, it is not always clear whether exposure can be beneficial, because it offers your body the chance to build allergy-busting antibodies, or whether complete avoidance of an allergen for as long as possible will have better results. Thus, scientists still actively debate, for example, whether pregnant women should eat peanut butter so that the baby can learn in utero not to be allergic to the nuts, or whether babies do not yet have the strength to combat a potential peanut allergy and this early exposure is ultimately allergy-triggering.
Can You Get an Allergy for the First Time as an Adult?
We know that children can “outgrow” allergies, and that this transition is more likely to happen with egg or milk allergies than nut allergies. But can we develop new allergies as adults?
The answer, of course, is yes, and scientists suspect that here environment is playing a more dominant role over genetics. Several factors can lead to a change in our exposure to a given allergen and thus trigger a new allergy in adulthood. Moving to an area with new trees and grasses or getting a new pet both can introduce us to allergens as adults that we had not previously encountered.
There is also the possibility of dormant allergies finally reaching critical exposure during adulthood. In other words, we may encounter a particular allergen as a child, but not to a strong enough degree, only to build up to high enough levels of exposure as an adult. If we encounter an allergen while our immune system is weakened, like it is during pregnancy, we can also increase our chances of developing a related allergy.
Why Do Allergies Seem to be Getting Worse?
Studies show that the occurrences of allergies are on the rise, thus making the search for their cause even more important. Food allergists at Mount Sinai tracking peanut allergies found that rates increased from 0.4% in 1997 to 1.4% just thirteen years later in 2010. Many people with one allergy, like peanuts, also end up being allergic to other tree nuts as well, like walnuts or pecans.
As mentioned by the House Call doctor, researchers hypothesize that this increase in allergy rates could be linked to our hygiene practices. If our environment is too sterile and does not provide enough exposure to potential allergens, our immune system effectively gets bored and starts acting out against what would otherwise be harmless foods or plants.
There is also likely a link between the prevalence of allergies and the rising global temperatures on our planet. The higher temperatures and the related increase in carbon dioxide in the air both can allow plant life to thrive. More plant life means more pollen. No research, however, has been able to link GMOs (genetically modified organisms) to higher allergy rates.
The array and extent of allergies to which we are exposed and the state of our immune system upon exposure thus combine with our genetic predisposal toward an allergic response to ultimately determine whether an allergy will be triggered in our bodies. Isolating the separate components to this complex combination is extremely difficult, if not impossible. So it’s not surprising that researchers are still looking to identify clear links between allergies and their specific causes, whether they be environmental or genetic.
Until next time, this is Sabrina Stierwalt with Ask Science’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Ask Science on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.comcreate new email.
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About the Author
Dr Sabrina Stierwalt earned a Ph.D. in Astronomy & Astrophysics from Cornell University and is now a Professor of Physics at Occidental College.
