What Causes Allergies?

Frederick R. Jelovsek MD, MS

When your nose is runny and eyes are itchy you probably are just interested in relief; not in why this reaction is happening. Sometimes though, it is helpful to know the detail of how a medical condition is produced especially when it is one that is chronic and going to afflict you the rest of your life. Allergy is one such condition. People with allergies have genes that make them more likely to develop a bodily reaction to various substances they are exposed to.

The body’s immune system is the main protective mechanism to maintain health. It identifies and fights off bacteria, viruses, parasites, cancer cells, food and any foreign protein substance. Lymphocytes are one type of white cell in your blood and they are a major component of the immune system. As soon as a foreign protein enters the body, the lymphocytes identify the protein, fingerprint it and determine if it belongs to this body or not. “Lymphocytes act like traveling customs agents. Everywhere they go, they are busy checking the passports of every cell they encounter. Whenever they discover a cell that seems threatening, they immediately begin countermeasures against it. The biochemical process behind these countermeasures is amazing! (1)

Allergies result when this immune system is hypersensitive, overreactive. When the system misidentifies harmless proteins as serious enemies and then reacts out of proportion to the threat, you get symptoms from this major bodily battle. Those symptoms may be mildly annoying or a major illness. Usually for your immune system to overreact like this you must have a genetic tendency for it.

After the lymphocyte identifies the foreign protein (antigen) it goes back to a lymph node where it changes into a different type of white blood cell (mast cell). The mast cell manufactures a chemical called an immunoglobulin that is exactly configured like a laser ray to destroy the specific protein that the lymphocyte identified in the first place. Of the different immunoglobulins (IgA, IgD, IgE, IgG, IgM), Ig E is the class that forms an allergic reaction. They attach to other white blood cells in what is called the sensitizing exposure,

When the protein comes into the body again, at least 7-10 days after the sensitizing reaction, the IgE primed mast cells release many chemicals including histamine that try to destroy the “invading” protein. Histamine lowers the local blood pressure and causes itching and swelling . It can also cause wheezing, an itchy, runny nose, nausea, vomiting or diarrhea. That is why “anti- histamine” drugs are used to treat allergies.

Specific allergies can be identified either by a blood test for IgE or by a scratch test in which the suspected allergen is “scratched” into the skin to see if the body reacts to it with redness and swelling. A problem with specific identification of allergies, however is what is called cross-reactivity. Sometimes proteins of different but similar substances, e.g., shrimp and crab meat, can both cause an allergic response even though the body had previously been exposed to only one of them. Even so, allergen identification is very important so that you can avoid the offending allergen in the first place.

Now why is it important to know the mechanism of action for allergies? If there is a genetic disposition for your body to form allergic responses, there is not much you can do – correct? No. You basically have two practical choices for self-care. Identify the causative agents so you absolutely avoid them and treat with anti- histamines for mild but annoying allergic reactions. Fortunately there is a self home test for food allergies, Food allergy test kit, and also one that tests for grasses, molds, dust and cat allergies along with some common food allergies such as milk, eggs and wheat, MyAllergyTest. For other tests you will have to have a doctor’s order and have a blood drawn and sent to a special laboratory. If you are having serious reactions, see an allergist for allergen identification and treatment.

One last tip. The gold standard for diagnosing allergies are the scratch test sets applied in the allergist’s office. Many times, however, you may not want to suffer the reactions you get during testing or you may fear causing a new allergy by sensitizing through your skin to a new substance you are not already allergic to. The allergy doctor may prefer the scratch tests because they are more accurate but you can ask to have the blood test done instead, with subsequent scratch testing if needed, to narrow down the specific allergen from a general group of substances.

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What causes allergies?

To help answer this question, let’s look at a common household example. A few months after the new cat arrives in the house, dad begins to have itchy eyes and episodes of sneezing. One of the three children develops coughing and wheezing, especially when the cat comes into her bedroom. The mom and the other two children experience no reaction whatsoever to the presence of the cat. How can we explain this?

The immune system is the body’s organized defense mechanism against foreign invaders, particularly infections. Its job is to recognize and react to these foreign substances, which are called antigens. Antigens are substances that are capable of causing the production of antibodies. Antigens may or may not lead to an allergic reaction. Allergens are certain antigens that cause an allergic reaction and the production of IgE.

The aim of the immune system is to mobilize its forces at the site of invasion and destroy the enemy. One of the ways it does this is to create protective proteins called antibodies that are specifically targeted against particular foreign substances. These antibodies, or immunoglobulins (IgG, IgM, IgA, IgD), are protective and help destroy a foreign particle by attaching to its surface, thereby making it easier for other immune cells to destroy it. The allergic person however, develops a specific type of antibody called immunoglobulin E, or IgE, in response to certain normally harmless foreign substances, such as cat dander. To summarize, immunoglobulins are a group of protein molecules that act as antibodies. There are five different types; IgA, IgM, IgG, IgD, and IgE. IgE is the allergy antibody.

(In 1967, the husband and wife team of Kimishige and Teriko Ishizaka detected a previously unrecognized type of immunoglobulin in allergic people. They called it gamma E globulin or IgE.)

In the pet cat example, the dad and the youngest daughter developed IgE antibodies in large amounts that were targeted against the cat allergen, the cat dander. The dad and daughter are now sensitized or prone to develop allergic reactions on subsequent and repeated exposures to cat allergen. Typically, there is a period of “sensitization” ranging from months to years prior to an allergic reaction. Although it might occasionally appear that an allergic reaction has occurred on the first exposure to the allergen, there must have been a prior contact in order for the immune system to be poised to react in this way.

Allergies

IgE is an antibody that all of us have in small amounts. Allergic persons, however, produce IgE in large quantities. Normally, this antibody is important in protecting us from parasites, but not from cat dander or other allergens. During the sensitization period, cat dander IgE is being overproduced and coats certain potentially explosive cells that contain chemicals. These cells are capable of causing an allergic reaction on subsequent exposures to the dander. This is because the reaction of the cat dander with the dander IgE irritates the cells and leads to the release of various chemicals, including histamine. These chemicals, in turn, cause inflammation and the typical allergic symptoms. This is how the immune system becomes exaggerated and primed to cause an allergic reaction when stimulated by an allergen.

On exposure to cat dander, the mom and the other two children produce other classes of antibodies, none of which cause allergic reactions. In these non-allergic members of the family, the dander particles are eliminated uneventfully by the immune system and the cat has no effect on them.

What causes allergic reactions

Whether it’s runny, itchy or stuffed, your nose knows what’s bothering it. But do you know what’s wrong with your nasal passages? Understanding allergies isn’t difficult, but it is the first step toward building a healthy alliance with your nose, eyes, lungs, and sinuses.

Allergies are the result of the immune system’s mistaken response to a harmless substance. Normally, the immune system stands guard and defends your body against intruders that can be dangerous to your health, such as viruses and bacteria. When it does its job well, your immune system keeps you from getting sick every time an ill-intentioned germ finds its way into your body.

In some people, however, the immune system has difficulty distinguishing between the good guys (or, at least, the neutral guys) and the bad guys. Like a nervous rookie, it sees danger everywhere and overreacts. A hyperreactive immune system pulls out all the stops for substances that won’t do you any actual harm, such as dust, pollen, and animal dander. These innocuous substances are called allergens.

When people who have allergies encounter an allergen, their immune system produces antibodies, called IgE antibodies, that are specific to that substance — ragweed, for instance, or cat dander.

Thousands of these antibodies bind to the surface of special cells in body tissue called mast cells, which then lie in wait for your next exposure to that specific allergen. While they are waiting, these mast cells absorb many different chemicals from the blood that will aid in the body’s defense; they store these chemicals in tiny granules. When you’re reexposed to the allergen, the allergen binds to the IgE antibodies on the surface of the mast cells, causing the mast cells to release the chemicals. One of the chemicals, histamine, is probably familiar to you. It is one of the biggest players in the allergic response system and causes many of the reactions, such as runny nose, sneezing, and itchy and watery eyes, that we describe as allergies.

Most anti-allergy medications block the histamine from binding to its receptor and are called antihistamines. The allergic reaction can have both an early and a late phase. Typically the early phase may start within a few minutes of exposure, while the late phase may start several hours after the initial exposure. The early phase is caused by the release of those chemicals stored in the granules in the mast cells. The late phase reaction is caused by other inflammatory cells recruited into the area.

What Causes Allergies

The substances that cause allergic disease in people are known as allergens. “Antigens,” or protein particles like pollen, food or dander enter our bodies through a variety of ways. If the antigen causes an allergic reaction, that particle is considered an “allergen” – and antigen that triggers an allergic reaction. These allergens can get into our body in several ways:

Inhaled into the nose and the lungs. Examples are airborne pollens of certain trees, grasses and weeds; house dust that include dust mite particles, mold spores, cat and dog dander and latex dust.

Ingested by mouth. Frequent culprits include shrimp, peanuts and other nuts.

Injected. Such as medications delivered by needle like penicillin or other injectable drugs, and venom from insect stings and bites.

Absorbed through the skin. Plants such as poison ivy, sumac and oak and latex are examples.
What Makes Some Pollen Cause Allergies, and Not Others?

Plant pollens that are carried by the wind cause most allergies of the nose, eyes and lungs. These plants (including certain weeds, trees and grasses) are natural pollutants produced at various times of the year when their small, inconspicuous flowers discharge literally billions of pollen particles.

Because the particles can be carried significant distances, it is important for you not only to understand local environmental conditions, but also conditions over the broader area of the state or region in which you live. Unlike the wind-pollinated plants, conspicuous wild flowers or flowers used in most residential gardens are pollinated by bees, wasps, and other insects and therefore are not widely capable of producing allergic disease.

What is the Role of Heredity in Allergy?

Like baldness, height and eye color, the capacity to become allergic is an inherited characteristic. Yet, although you may be born with the genetic capability to become allergic, you are not automatically allergic to specific allergens. Several factors must be present for allergic sensitivity to be developed:

The specific genes acquired from parents.
The exposure to one or more allergens to which you have a genetically programmed response.
The degree and length of exposure.
A baby born with the tendency to become allergic to cow’s milk, for example, may show allergic symptoms several months after birth. A genetic capability to become allergic to cat dander may take three to four years of cat exposure before the person shows symptoms. These people may also become allergic to other environmental substances with age.

On the other hand, poison ivy allergy (contact dermatitis) is an example of an allergy in which hereditary background does not play a part. The person with poison ivy allergy first has to be exposed to the oil from the plant. This usually occurs during youth, when a rash does not always appear. However, the first exposure may sensitize or cause the person to become allergic and, when subsequent exposure takes place, a contact dermatitis rash appears and can be quite severe. Many plants are capable of producing this type of rash. Substances other than plants, such as dyes, metals, and chemicals in deodorants and cosmetics, can also cause a similar dermatitis.

What Causes Allergies? – Discussion

Having allergies can be such a drain on your body, and figuring out what causes allergies can be a constant quest.

Physically, you may feel as though you are constantly blowing your nose or sneezing, and mentally, you may find yourself afraid to get anywhere near the known culprits.

If a friend has a cat, for example, you may find yourself making excuses for not going to her house due to the reaction you get every time you visit. It’s a terrible way to live, and often times, getting to the root of the cause can be helpful and aid in explaining just why this is happening to you.

Some people suffer from all sorts of allergies their whole life through, while others never get a sniffle from them a day in their life. So what causes allergies? Why do some people suffer from childhood while others never have to think about allergies whatsoever?

Who is to Blame? What Causes Allergies?

Rather than blaming the culprits or allergens themselves, look further. The root cause of many allergies is actually your very own immune system. Hard to believe, but it’s true. Your immune system mistakes the known allergens as a serious threat and attacks them – the result is an allergy that can cause you to suffer for years and years.

Although it is not a certainty, there is a great likelihood for being pre-disposed to allergies if you have a genetic history of them. If you come from parents who are allergy sufferers, you are at a much higher risk of developing them at some point in your life.

Technically speaking, what causes allergies? Allergic reactions themselves are triggered by a chemical within your body called histamine, and though initial or limited exposure to a given allergen may not present any problems, at some point your body will react.

Many people develop allergies later on in their life, after years of being exposed to the culprit, and they cannot figure out why. It can take one exposure when you have a weakened immune system, and then out of the blue you are now a known allergy sufferer. This can be frustrating and troublesome for many adults, but the problem may have always been there, and it just took one exposure to bring it about.

Making the Right Choices

Consider the immune system to be the gatekeeper of sorts – when it’s down, anything can happen, and that one exposure can turn into an allergy that you have to battle your whole life through. Add to it any genetic predisposition, and you have found the underlying reasons for what causes allergies and why you may be suffering from them day in and day out.

The good news is, although a genetic predisposition can make allergies more likely, there are steps you can take to prevent allergies from ruling your life, and even heal the condition.

Environment and diet play a vital role in all health conditions, and this holds true for what causes allergies as well. If you live in an atmosphere full of chemicals and breathe these in day in and day out, there is certainly a likelihood that this will either bring on or amplify allergies within your body. Learning to keep your house clean and to handle such needs with the most natural supplies which are as free of chemicals as possible is a great start. It’s also imperative to keep a healthy diet.

Consuming foods that are processed, fried, or full of preservatives can contribute to the likelihood of allergies or flare ups. Ensuring that you eat a diet that is not only rich in nutrients but free of preservatives and other additives used in processed foods can help in the prevention and even the cure of allergies.