Here’s What Happens to Your Body During Anaphylaxis

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According to the Centers for Disease Control and Prevention, allergies affect more than 50 million Americans every year—and anaphylaxis, the most severe allergic reaction, affects at least 1.6 percent of the general population [PDF]. Here’s the science of what happens to the body during anaphylactic shock.

ALLERGEN EXPOSURE

In a person with allergies, cells sometimes identify foreign but innocuous stimuli as major threats. Why some people are allergic to certain things while others are not is a mystery science hasn't yet solved, but we do know how it happens: through a process called sensitization.

Here’s how it works. When the body encounters a foreign substance, also called an antigen, immune system cells deliver some of substance's molecules to T-helper cells living in the lymph nodes. Those cells also bring along a type of molecule that informs a T-helper cell it’s time to stage an immune response. Known as a costimulatory molecule, it's necessary to activate any type of immune system reaction involving T cells, whether you have allergies or not.

Being exposed to an antigen "primes" a T-helper cell, turning it into a Th2 cell. Primed Th2 cells release proteins called interleukins, which do two things: First, they interact with another type of immune cell called B cells to produce infection-fighting antibodies that bind to mast cells, which contain chemical particles they'll release in the presence of an antigen. Second, the interleukins activate eosinophils, a type of white blood cell that discharges toxic substances to destroy invading cells (and, occasionally, host cells). In this process, the immune system identifies the "threat" and deploys cells prepared to fight it. The immune system's elevated level of awareness of and preparation against the antigen reclassifies the substance as an allergen—a considerably more dangerous threat.

Because an allergy only develops after this process, a person allergic to strawberries, for example, will only experience a reaction the next time they eat something containing strawberries. New allergies can pop up at any point in your life.

An immune system on allergies is a little bit like a brain that can't distinguish a piece of lint from a spider: unable to relax, constantly on guard against every potential threat. After initial exposure, the mast cells activated during the sensitization phase are still equipped with allergen-specific antibodies and remain combat-ready, prepared to respond immediately should a second exposure ever occur. If it does—and it probably will—here’s what you can expect to happen.

ALLERGIC REACTION

If two or more allergen molecules bind to a sensitized mast cell, the mast cell releases inflammatory mediators that produce an allergic reaction. These mediators include substances like histamine and more of the interleukins that, in turn, activate eosinophils, Th2 cells, and basophils (another type of white blood cell). In a non-allergic reaction, mediators produce helpful inflammation that prevents infection and initiates healing—but those same symptoms can be annoying and even dangerous when the immune system attacks an otherwise benign allergen. Mast cells also release leukotrienes, which recruit more immune cells to the area and speed up the reaction. That leads to what Stanford University researcher Tina Sindher calls a “‘chain reaction’ of allergic inflammation.”

With the release of histamine, you might experience both bronchial contraction—which makes it more difficult to breathe—and blood vessel dilation. The latter makes it easier for blood to flow to affected areas, but it also makes blood vessels more permeable, allowing blood to escape from the blood vessel walls and flow into the spaces between cells and causing swelling and hives.

For most, these symptoms are merely uncomfortable; they can occur as late as eight to 12 hours after initial exposure, long after the allergen is gone, and can be alleviated with an antihistamine like Benadryl. But for a person with severe allergies, a life-threatening allergic response can occur within minutes: Their airways will constrict so much they won't be able to breathe, and their blood vessels will be unable to contract, which can lead to a drop in a blood pressure and keep veins from getting blood back to the heart. The combination of airway constriction and blood vessel dilation can make it impossible for the body to supply enough oxygen to major organs—that's anaphylactic shock.

The only way to stop anaphylaxis in its tracks is with epinephrine, more commonly known as adrenaline. Adrenaline is a hormone naturally produced by the adrenal glands to help generate the "fight or flight" response in emergency situations. It works by constricting certain blood vessels, increasing blood pressure, and relaxing airways, counteracting all the reactions produced by histamines.

According to Sindher, it’s important to use epinephrine immediately if you're at risk for anaphylactic shock. “There’s a general belief out there that epinephrine should only be used in the worst-case scenario,” she tells Mental Floss. “In fact, most of the complications we see in food allergic reactions are due to delayed use in Epi. Antihistamines can be helpful in treating the symptoms of itching and congestion, but they do not help stop an allergic reaction.”

THE FUTURE OF ALLERGY TREATMENT

Researchers like Sindher are still trying to understand what causes allergies, and why the prevalence of food allergies has increased over the past few decades. Sindher’s main goal is to find new ways of treating (and hopefully curing) allergies. The most established technique (for food allergies, at least) is oral immunotherapy, where allergic individuals gradually eat more of their allergen until they can have small amounts without experiencing a reaction. That’s usually done extremely gradually, over the course of months or years, and always under the supervision of a certified allergist.

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Sindher says scientists are still testing other types of immunotherapy treatments and vaccinations in clinical trials: “A lot of research is going into trying to identify the causes so we can be successful in the prevention as well as treatment of food allergies.”

Until that happens, though, doctors say the best course of action is to be careful around allergens. Medications are useful and necessary, but prevention is the name of the game when it comes to allergies.

Learn Travel Blogging, Novel Writing, Editing, and More With This $30 Creative Writing Course Bundle

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Winter is Coming: Why Some People Seem to Feel Colder Than Others

Work blanket? Check. Hot tea? Check. Writing gloves? Check.
Work blanket? Check. Hot tea? Check. Writing gloves? Check.
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For a few weeks a year, as winter turns into spring, or summer gives way to fall, people in heavy coats coexist with those in sandals and shorts. Similarly, in an office where the thermostat is set at 74°F, some workers will be comfortable in short sleeves, while others will be wearing sweaters and scarves.

Underlying this disagreement are the different ways people perceive cold—and scientists are still trying to understand them.  

Men, Women, and Metabolism

In work settings, men and women often have different opinions about the ideal temperature. A 2019 study found that women performed better in math and verbal tasks at temperatures between 70°F and 80°F, while men did better below 70°F. The researchers proposed that gender-mixed workplaces might boost productivity by setting the thermostat higher than the current norm (which the Occupational Safety and Health Administration suggests should be between 68°F and 76°F).  

The discrepancy has a known physical basis: Women tend to have lower resting metabolic rates than men, due to having smaller bodies and higher fat-to-muscle ratio. According to a 2015 study, indoor climate regulations are based on an “empirical thermal comfort model” developed in the 1960s with the male workers in mind, which may overestimate female metabolic rates by up to 35 percent. To compound the problem, men in business settings might wear suits year-round, while women tend to have more flexibility to wear skirts or sundresses when it's warm outside.

Culture and the Cold

Cultural factors are also involved. European visitors are habitually alarmed by the chilly temperatures in American movie theaters and department stores, while American tourists are flabbergasted at the lack of air conditioning in many European hotels, shops, and offices. The preferred temperature for American workspaces, 70°F, is too cold for Europeans that grew up without the icy blast of air conditioners, Michael Sivak, a transportation researcher formerly at the University of Michigan, told The Washington Post in 2015.

The effects of cultural change on the human ability to withstand extreme temperatures can be dramatic. In the 19th century, 22 percent of women on the Korean island of Jeju were breath-hold divers (haenyeo). Wearing thin cotton bathing suits, haenyeo dove nearly 100 feet to gather shellfish from the sea floor, holding their breath for more than three minutes in each dive. In winter, they stayed in 55°F-57°F water for up to an hour at the time, and then warmed up by the fire for three of four hours before jumping back in.

In the 1970s, haenyeo starting wearing protective wet suits. Studies conducted between the 1960s and the 1980s showed that their tolerance for cold diminished [PDF].

Blame Your Brain

Beyond the effects of cultural practice and body composition, scientists have started to identify the cognitive factors that influence our temperature perception. It turns out that what feels unpleasantly cold versus comfortably chill is partly in our own minds.

One example is the phenomenon described as “cold contagion.” A 2014 study asked participants to view videos of people immersing their hands in visibly warm or cold water. Observers not only rated the hands in cold water as cooler than those in hot water, but their own hands became cooler when watching the cold-water videos. There was no comparable effect for the warm water videos, however. The findings suggest that we may feel colder when surrounded by shivering people at the office than if we're there by ourselves, even when setting the thermostat at the same temperature in both cases.

Other studies highlight the psychological aspects of temperature perception. Experimental participants at the Institute of Biomedical Investigations in Barcelona, Spain, watched their arms become blue, red, or green by means of virtual reality, while the neuroscientist Maria Victoria Sanchez-Vives and her team applied heat to their actual wrists. As the temperature increased, participants felt pain earlier when their virtual skin turned red than when it turned blue or green.

Subjectivity in temperature perception has led to some creative treatments for burn patients. In the 1990s, Hunter Hoffman, David Patterson, and Sam Sharar of the University of Washington developed a virtual-reality game called SnowWorld, which allows patients in hospital burn units to experience virtual immersion in a frozen environment. Amazingly, playing SnowWorld counteracted pain during wound care more effectively than morphine did.

“The perception of temperature is influenced by expectations,” Sanchez-Vives tells Mental Floss. “Putting one’s hand inside a virtual oven is perceived as ‘hot,’ while sticking one’s hand into a virtual bucket filled with iced water is perceived as ‘cold,’ despite being at room temperature in each scenario.”

In other words, if you expect to feel cold walking into the office or out on the street, chances are that you will.