20 Interesting Facts About Allergies

Spring is coming, so that means sunshine, flowers, and…allergies. Everyone’s heard of them, and many have experienced them themselves. But as with any widely known subject, there are plenty of misconceptions out there. So this time’s 20-facts post will be about how allergies work and help clarify some stuff you might have heard about them.

1. Allergies are the result of a specific inflammatory response to a normally harmless substance (allergen).

In medical terms, an allergy is specifically a type I hypersensitivity. That means it’s a result of B-cells (a type of immune cell) producing an antibody called immunoglobulin E (IgE), which is specific to an allergen. When other immune cells (mast cells and basophils) coated with IgE encounter the allergen, they release histamine and other inflammatory compounds. This causes the swelling and other symptoms seen in an allergic reaction.

The general public often lumps other similar reactions as “allergies”, but they aren’t true allergies because the mechanisms behind them are different. For example, some of the more unusual “allergies”, such as to nickel and gold, are actually type IV hypersensitivities and involve different immune cells.

2. The symptoms of an allergic reaction appear very quickly…

There are two kinds of type I hypersensitivity reactions. The first is immediate, and, as it suggests, it happens within minutes. This distinction can help determine whether it’s an allergy or something else like a foodborne illness or a cold, which often takes hours to days to manifest. The second is late-phase, and it involves the migration of other immune cells to the site of the allergen. This kind typically happens 2-24 hours after exposure.

3. …but manifest differently depending on what organ is affected.

The symptoms of an allergic reaction vary depending on what organ the allergen affects. Here’s a general list of them:

Nose: stuffed or runny nose, sneezing
Sinuses: thick nasal mucus, stuffed nose, facial pain
Eyes: redness and itchiness of eyelids, watery eyes
Airways: coughing, sneezing, wheezing, asthma, shortness of breath, possible airway constriction due to swelling
Ears: feeling of fullness, pain, impaired hearing
Mouth: tingling/itching feeling in parts of the mouth, swelling of lips or tongue
Skin: rashes, hives
Digestive tract: abdominal pain, bloating, vomiting, diarrhea

Usually, an allergic reaction is confined to a specific area. But serious allergic reactions can affect multiple organs. That’s called anaphylaxis, and it can lead to blocked airways and/or blood vessels. That’s why some severe allergic reactions can cause death in as little as 15 minutes.

4. Allergies are pretty common…

For most people, allergies aren’t something they worry about. But they’re actually surprisingly common. By some estimates, about 20-40% of people worldwide have some kind of allergy.

5. …but they seem to affect populations in developed regions more than developing ones.

Paradoxically, populations in more developed and affluent regions have a higher incidence of allergies than those in developing regions. It’s weird because people in developed countries generally have access to cleaner food and water and are less exposed to environmental pathogens and debris that could cause allergies.

It’s led researchers to come up with a “hygiene hypothesis” to explain the discrepancy. That hypothesis proposes that the developing immune system, when in too sterile an environment, doesn’t get primed correctly to deal with threats to the body. It’s essentially not “kept busy enough” with bacteria, viruses, and other pathogens, and thus becomes overactive and attacks harmless particles.

6. Just eight foods account for about 90% of all food allergies.

These “big eight” require special labeling on foods. They are milk, eggs, fish, shellfish, tree nuts, peanuts, soybeans, and wheat.

7. People with a latex allergy might also be allergic to certain foods.

Some of the proteins in certain foods are chemically similar enough to latex that they can “cross-react” in people with latex allergies. These foods include avocadoes, mangoes, bananas, kiwis, tomatoes, chestnuts, papayas, and potatoes.

8. Genetics plays a significant role in whether you’re allergic to something or not.

Allergies tend to run in families. That’s why family history is important in helping to diagnose an allergy. Identical twins have a 70% chance of sharing the same allergy, and fraternal twins have a 40% chance.

9. Tests for allergies aren’t always 100% accurate.

The typical tests for allergic reactions are blood tests and skin (skin prick or skin patch) tests. But these tests can sometimes show false positives or negatives. As a result, doctors will sometimes do a supervised “challenge” test (exposure to allergen in increasing amounts) as a follow-up. There are a number of factors that can interfere with a test’s results, such as medications and sun exposure.

There are also a bunch of “alternative” testing methods, such as cytotoxic food testing, kinesiology, and iridology. These, however, are unreliable, have no basis in science, and should be ignored completely.

10. You can outgrow some allergies…

For some allergies, such as egg, milk, and soy, it’s possible to develop a “spontaneous immune tolerance” and essentially outgrow them. Many young children with these allergies outgrow them by kindergarten. However, other allergies, such as to peanuts, tree nuts, and shellfish, tend to stick around for life. For example, only about 20% of those with peanut allergies spontaneously resolve them.

11. …but it’s also possible acquire new allergies.

This typically happens when you get introduced to a new allergen that you haven’t encountered before (ex. when you move to a new place). Shellfish allergy is one example of an allergy that generally happens later in life. Another interesting example is the allergy to red meat. It’s linked to a bite from a Lone Star tick.

12. Stress can worsen existing allergies.

Obviously, when stressed, people generally have a more negative view on just about everything bad, including allergy symptoms. But there’s also a physical way that stress affects symptoms. The mechanisms aren’t entirely understood, but the general understanding is that stress releases certain hormones that can exaggerate the immune system’s response to allergens. There’s some evidence to suggest that reducing stress in people who are highly prone to allergies can reduce their symptoms.

13. There’s no such thing as a hypoallergenic cat or dog.

Some people mistakenly think that the stuff that makes you allergic to cats and dogs is the fur. So that leads them to think that animals that shed fur less or have less fur to begin with are hypoallergenic. That’s actually not the case. The proteins that cause pet allergies are present in the animal’s saliva, sweat, and urine, which get transferred to the animal’s dead skin flakes (pet dander). While a non-shedding breed may not release as much dander into the environment, there’s no breed that secretes zero allergens.

The only practical solution for people who are allergic to pets but still want one is to test how they fare with a particular breed on a case-by-case basis.

14. Some allergies can be treated through allergen immunotherapy.

This kind of treatment is mainly for environmental allergies (ex. pollen), insect bite allergies, and asthma. It’s a gradual exposure to more and more of the allergen until the body becomes desensitized to it. Note that this isn’t a full cure, since desensitization only reduces the body’s reaction to an allergen to a manageable level, not completely eliminate it. Symptoms can return once the treatment stops.

As of now, allergen immunotherapy isn’t recommended for food allergies due to lack of evidence of effectiveness and a high risk of adverse side affects.

15. Flu vaccines are safe for people with egg allergies.

Many vaccines are made using chicken eggs, including the one for the flu. But they’re generally completely safe for people with egg allergies. The vaccines don’t contain significant enough amounts of egg proteins to cause allergic reactions. Only those with severe reactions to eggs need to consult with their doctor before getting one. For them, an egg-free alternative vaccine (Flublok) is available.

16. It’s generally okay to feed children as young as 6 months old nuts, eggs, and fish.

The advice that young children avoid these foods came from the American Academy of Pediatrics in 2000. However, it was later withdrawn in 2008 due to lack of evidence for the recommendation. As long as the food doesn’t pose a choking hazard and is properly cooked, it’s safe for children who don’t have a family history of the allergy to it.

In fact, newer evidence is actually pointing to the reverse. It suggests (not yet conclusively, though) that early introduction to these possibly allergenic foods helps prevent allergies to them later on in life.

17. There’s no such thing as a “gluten allergy”.

With the recent gluten-free trend, many people self-diagnosed themselves to be allergic to gluten. Only problem is that’s not really a thing. There’s a known allergy to wheat, and that’s caused by any of the storage proteins in wheat (gluten is only one of them). So using the term “gluten allergy” when referring to a wheat allergy is pretty misleading.

There are people with celiac disease, who experience severe reactions when eating gluten. But celiac disease is an autoimmune disease, not a food allergy. Others may have a food sensitivity to gluten (non-celiac gluten sensitivity), but food sensitivities also aren’t the same as food allergies.

18. The pollen from flowers usually isn’t to blame for pollen-related allergies.

The stereotypical pollen source for pollen allergies is a flowering plant. But that’s not usually the case. The pollen from typical flowering plants is too heavy/sticky to travel very far. That’s why many of them need help from insects and other pollinators to transfer pollen. Instead, the pollen that causes hay fever usually comes from grasses, trees, and weeds. Ragweed, pine trees, and birch trees are some examples.

19. CT scans are fine, even if you have a seafood allergy.

In the 1970s, researchers noted that about 15% of people who had bad reactions with the radiocontrast dye used during CT scans also had a shellfish allergy. Since iodine is present in both, they presumed that the iodine was the cause.

But that’s not really possible because iodine is naturally present in the body and is necessary for thyroid function. It’s since been shown that the substance that causes shellfish allergies isn’t iodine but a particular protein, which isn’t in the dye. Bad reactions to the radiocontrast dye and shellfish allergies are completely unrelated. Even so, it seems many doctors still ask about shellfish allergies before administering the dye.

20. Some allergies seem to be getting more common.

Hay fever and asthma are particular examples. They’ve been increasing in frequency in the Western world for the past 2-3 decades. Since the change is over too short a time period for generational differences to be significant, scientists have proposed that they might be due to environmental or lifestyle changes, such as reduced exercise, more time staying indoors, increased focus on hygiene, and dietary changes that alter the microbial population in the gut.