It’s the playoffs -- the climactic end of baseball's post-season -- and in Chicago, that means watching your favorite team with an ice-cold beverage in one hand and a salty snack in the other. No doubt the go-to snack for an afternoon at the ballpark is a bag of roasted peanuts. However, for an increasing number of people, this salty snack is a dangerous health hazard. More and more people cannot even walk into the hallowed halls of Wrigley Field for fear of inducing a serious allergic reaction. What makes a person susceptible to peanut allergies? And how can eating as little as 1/100th of a peanut can send someone to the hospital?
Our immune system’s job is to identify and protect us from harmful agents, or pathogens, that can cause disease. One branch of our immune system, called the adaptive immune system, builds a memory of pathogens we have encountered. This helps it fight back quickly next time we’re exposed to the same threat.
Essentially, people with peanut allergies develop a hypersensitive adaptive immune response to peanuts. Upon re-exposure to a peanut, their system goes into overdrive to protect against the mistakenly perceived pathogen. This hypersensitive response causes symptoms like itchiness, hives, and swelling. The most severe allergic reactions, like anaphylaxis, include swelling of the throat, shortness of breath, vomiting, and low blood pressure.
Severe reactions to peanuts are on the rise in Western countries in recent years. Self-reported peanut allergies increased 3.5-fold in the US between 1997 and 2008. Due to this increase, some mothers avoided peanuts during pregnancy and some parents stopped feeding peanuts to their young children in the hope that they would not develop peanut allergies. But despite these parental efforts, kids who have never eaten a peanut still get peanut allergies! What gives?
New evidence suggests that biological predispositions can contribute to peanut allergies. For example, mutations in a gene called filaggrin have been significantly correlated with peanut allergies. Filaggrin is essential for skin health, and mutations in this gene are associated with skin sensitivities such as eczema. Studies show that peanut exposure (on the skin) triggers an allergic immune response in mice and humans with these pre-existing skin sensitivities.
However, skin sensitivities like these do not fully explain why kids in Western countries have a much higher rate of peanut allergies compared to the rest of the world. For example, populations of Jewish children in the UK have a 10-times higher rate of peanut allergies than children of similar heritage in Israel. The key to this difference may lie in diet differences early in life. Babies in the UK typically are not fed peanuts while babies in Israel enjoyed Bamba, a peanut-flavored puff snack. Given this dietary difference, some scientists have hypothesized that early consumption of peanuts may actually help prevent allergies.
In 2015, British scientists designed an experiment aimed at understanding this connection in infants with existing sensitivities. In the Learning Early About Peanut Allergy (or LEAP) study, infants who already had skin sensitivities or other food allergies were split into two groups. The first group of babies avoided peanuts until the age of 5 and the second group started to eat peanuts as infants. The LEAP study showed that 17% of children who avoided peanuts developed an allergy by the age of 5. Astoundingly, by contrast, only 3% of 5-year-olds who ate peanuts during development became allergic! A follow-up study in 2016 reported that the children who tested peanut-tolerant were still able to eat peanuts with no reaction, even after pausing their consumption for a year.
Now, this does not mean parents should start feeding their babies peanut butter and jelly sandwiches straight away. There are still several understudied factors that make a person susceptible to a peanut allergy, and studies on infant oral exposure are still preliminary. However, these studies indicate that kids with existing skin and immune sensitives may be more likely to develop peanut allergies when they avoid eating peanuts as an infant and are exposed to peanuts through their skin.
These discoveries bring us one step closer to understanding the alchemy of food allergies in general. Maybe in the future, with an increased understanding of the risk factors for developing allergies, more kids can experience the joy of watching a baseball game from the stands instead of the couch.