TedEd: Allergies

Why do people get allergies?

​TedEd

Anyone with an allergy has their origin story, a tale of how they discovered that their immune system goes haywire when some arbitrarily particular molecule gets into their body. There are hundreds of millions of these stories. In the US alone, an estimated 18 million people suffer from hay fever, and food allergies affect millions of American children. The prevalence of allergies in many other countries is rising. The list of allergens includes — but is not limited to — latex, gold, pollen (ragweed, cockleweed and pigweed are especially bad), penicillin, insect venom, peanuts, papayas, jellyfish stings, perfume, eggs, the feces of house mites, pecans, salmon, beef and nickel.

Multiple Choice

How many people in the US have hay fever?

• 18 hundred

• 18 thousand

• 18 million

• 18 billion

Multiple Select

Select ALL of the types of allergens listed in the reading below:

• perfume

• eggs

• flowers

• pecans

Multiple Select

Select ALL of the types of allergens listed in the reading below:

• ragweed

• jellyfish stings

• peanuts

• penicillin

Once these substances trigger an allergy, the symptoms can run the gamut from annoying to deadly. Hives appear, lips swell. Hay fever brings sniffles and stinging eyes; allergies to food can cause vomiting and diarrhea. For an unlucky minority, allergies can trigger a potentially fatal whole-body reaction known as anaphylactic shock.

Multiple Choice

Which of the following is NOT a type of allergic response?

• hives

• vomiting

• cough

• sniffles

Multiple Choice

What is the name of the fatal allergic response that can happen?

• sudden cardiac arrest

• anaphylactic shock

• diabetic shock

• electrocution

Allergies usually, but not always, show up for the first time during childhood. But why do some people get allergies and others don’t? Allergies tend to run in families, so genetics may be one culprit. In fact, errors in a gene that helps regulate the immune system are associated with higher rates of allergies. The environment you grow up in matters, too. Being exposed to an allergen as a baby makes you less likely to actually develop an allergy to it. People who grow up on farms, in big families, and in the developing world also tend to have fewer allergies, although there are plenty of exceptions, partly thanks to genetics. The idea is that as children, they encounter more of the microbes and parasites that co-evolved with traditional hunter-gatherer societies, and that an immune system toughened up by a barrage of pathogens is less likely to overreact to allergens.

Multiple Choice

True or False: Allergies always show up for the first time in childhood.

• True

• False

Multiple Choice

True or False: Allergies tend to run in families

• True

• False

Multiple Select

Pick ALL of the factors that make someone less likely to have allergies when they are older:

• getting vaccinated

• growing up on a farm, in a big family, or in a developing country

• being exposed to an allergen as a baby

• washing hands frequently

For allergy sufferers, the current treatment options are limited: antihistamines can stop the inflammation response, steroids can help dial down the immune system, and EpiPens can save lives. A more permanent option is immunotherapy. Deliberate, controlled exposure to gradually increasing amounts of an allergen can teach the immune system that it isn’t dangerous after all.

Multiple Select

What are treatment options for current allergy sufferers? Select all that apply.

• vaccines

• EpiPen

• antihistamines

• steroids

Multiple Choice

Controlled exposure to increasing amounts of an allergen to teach the immune system that it isn't dangerous is a process known as what?

• epinephrine

• chemotherapy

• radiation

• immunotherapy

There might be more effective treatments if scientists understood allergies, but a maddening web of causes underlies allergic reactions. Cells are aroused, chemicals released, signals relayed. Scientists have only partially mapped the process. And there’s an even bigger mystery underlying this biochemical web: why do people get allergies at all?

The hygiene hypothesis proposes that our immune system overreacts to harmless substances because there aren’t enough harmful ones around to train it to discriminate. But the question remains of why some things (pollen, a bee sting) are much more likely than others (peas, a mosquito bite) to cause a severe allergic reaction. One theory is that allergens have certain proteins that resemble those found on parasitic worms (ironically, the very same type of creature that can be used to treat allergies.) When our immune system recognizes a parasitic worm, it produces the same type of antibodies that respond to allergens—antibodies which are actually fairly unusual today.

Multiple Choice

What hypothesis proposes that our immune system overreacts to harmless substances because it hasn't been exposed to enough to train itself?

• the pollution hypothesis

• the nutrition hypothesis

• the hygiene hypothesis

• the exposure hypothesis

Multiple Choice

Some allergens have certain ___________ that our immune systems recognize as ones found in parasitic worms.

• carbohydrates

• proteins

• amino acids

• cells

 However, a competing theory suggests that these “harmless” substances actually aren’t: that we respond to allergens not because they remind our immune systems of parasitic worms, but because they actually physically damage our cells, shredding them to pieces. In this model, allergies are the first line of defense against toxic molecules, which our ancestors likely encountered in their environment much more often than we do today.

Multiple Choice

True or False: Another competing theory suggests that our immune system attacks allergens because the allergens actually physically damage our cells.

• True

• False