Allergies: causes, diagnosis and treatment


An allergic reaction occurs when a person’s immune system becomes hypersensitive to certain substances, such as food, pollen, drugs, or bee venom.

A substance that causes an allergic reaction is called an allergen. Many allergens are everyday substances that are harmless to most people. However, anything can be an allergen if the immune system has a specific type of adverse reaction.

One of the roles of the immune system is to destroy harmful substances in the body. If a person is allergic to a substance, their immune system will react as if the substance is harmful and try to destroy it.

More than 50 millions in the United States, people have an allergic reaction every year. This reaction can lead to symptoms such as swelling. If the swelling affects the airways, it can be fatal.

In this article, learn about the risk factors, symptoms and treatments associated with allergies.

Allergies develop when a person’s immune system overreacts to substances that are usually harmless.

The first time a person is exposed to an allergen, they usually do not experience a reaction. It often takes time for the immune system to develop sensitivity to the substance.

Over time, the immune system learns to recognize and remember the allergen. In doing so, it begins to make antibodies to attack it when exposure occurs. This accumulation is called sensitization.

Some allergies are seasonal. For example, hay fever symptoms can peak between April and May, when the number of tree and grass pollens in the air is higher. A person may experience a more severe reaction as the number of pollen increases.

Is it an allergy or an intolerance? Check out the differences here.

An allergic reaction causes inflammation and irritation. However, the specific symptoms will depend on the type of allergen. For example, allergic reactions can occur in the intestine, skin, sinuses, respiratory tract, eyes, or nasal passages.

Below are some triggers and the symptoms they can cause in people with allergies.

Dust and pollen

  • a stuffy or congested nose
  • itchy eyes and nose
  • a runny nose
  • puffy and watery eyes
  • a cough


  • vomiting
  • a swollen tongue
  • tingling in the mouth
  • swelling of the lips, face and throat
  • stomach cramps
  • shortness of breath
  • rectal bleeding, mainly in children
  • itching in the mouth
  • diarrhea

Insect bites

  • wheezing
  • severe swelling at the bite site
  • a sudden drop in blood pressure
  • itchy skin
  • shortness of breath
  • commotion
  • hives, or a red, very itchy rash that spreads throughout the body
  • dizziness
  • a cough
  • chest tightness


  • wheezing
  • swelling of the tongue, lips and face
  • a rash
  • itching

If symptoms worsen, anaphylaxis may develop.

Anaphylaxis is the most serious form of allergic reaction. This is a medical emergency and can be life threatening. Anaphylaxis can develop rapidly, with symptoms appearing within minutes or hours of exposure to the allergen.

Research suggests that anaphylaxis most often affects skin and respiratory system.

Some symptoms include:

  • hives, flushing and itching
  • difficulty in breathing
  • wheezing
  • swelling
  • Low blood pressure
  • changes in heart rate
  • dizziness and fainting
  • loss of consciousness

Recognizing these symptoms can be crucial to receiving timely treatment.

Learn more about the symptoms of anaphylactic shock here.

When an allergic reaction occurs, the allergens bind to antibodies the body makes called immunoglobin E (IgE). Antibodies fight foreign and potentially harmful substances in the body.

Once the allergen binds to IgE, specific types of cells, including mast cells, release chemicals that trigger the symptoms of the allergic reaction.

Histamine is one of these chemicals. It causes tightening of the muscles of the airways and the walls of blood vessels. It also causes the lining of the nose to produce more mucus.

People may have a higher risk of allergies if they are under 18 or have a personal or family history of asthma or allergies.

Some researchers suggested that people born by cesarean section may also have a higher risk of allergies, as they do not have exposure to the mother’s microbiome during childbirth.

Potential allergens can appear almost anywhere.

In theory, a person can be allergic to any food. Specific components, such as gluten, the protein found in wheat, can also trigger reactions.

The eight foods probably cause allergies are:

  • eggs, especially the whites
  • fish
  • milk
  • peanuts
  • nuts
  • shellfish
  • wheat
  • soy

Learn more about food allergies here.

Some other common allergens include:

  • animal fur, dander, skin flakes, or saliva
  • mold and mildew
  • medications, such as penicillin
  • insect stings and bites
  • cockroaches, caddisflies, midges and moths
  • plant pollens
  • Household chemicals
  • metals, such as nickel, cobalt, chromium and zinc
  • latex

If a person thinks they have an allergy, their doctor can help them identify the cause of the reaction.

The person should be prepared to explain:

  • all the symptoms they noticed
  • when and how often they occur
  • what seems to be causing them
  • any family history of allergies
  • whether or not other household members have a similar reaction

The doctor may recommend tests or refer the person to a specialist.


Here are some examples of allergy tests:

  • Blood tests: These measure the levels of IgE antibodies directed against specific allergens in the immune system.
  • Skin tests: A doctor will prick the skin with a small amount of a possible allergen. If the skin reacts and becomes itchy, red, or swollen, the person may have an allergy.
  • Patch tests: To check for contact eczema, a doctor may stick a metal disc with a small amount of a suspected allergen on the person’s back. They will check for a skin reaction 48 hours later and then again after 2 days.

the American College of Allergy, Asthma and Immunology can help a person find a certified allergist.

The best way to deal with an allergy is to avoid the allergen, but that’s not always possible. In these cases, medical treatment can help.


Medicines do not cure an allergy, but they can help a person manage the symptoms of a reaction.

A lot treatments are available at the counter. Before using any medication, however, a person should speak with a pharmacist or doctor.

The options include:

  • Antihistamines: These block the action of histamine, which the immune system releases during a reaction.
  • Decongestants: These can help relieve a stuffy nose.
  • Corticosteroids: These are available as a pill, cream, nasal spray, or inhaler. They help reduce inflammation.
  • Immunotherapy: It can help a person develop long term tolerance. A person will take gradually increasing doses of the allergen, either as a tablet or as an injection.
  • Leukotriene receptor antagonists (antileukotrienes): These can help with some allergies if other treatments haven’t worked. Medicines block some of the chemicals that cause swelling.

Anaphylaxis is a life-threatening medical emergency that may require hospitalization.

If a person has difficulty breathing as a result of exposure to an allergen, they will need immediate treatment. This will usually be in the form of an auto-injector.

Using an auto-injector

the Food and Drug Administration (FDA) recommend that people at risk of anaphylaxis carry two epinephrine auto-injectors with them at all times. If one dose does not work, the person will need the second.

Use an auto-injector to give a measured dose of epinephrine (adrenaline) within minutes of the onset of severe symptoms. Someone should also call emergency services.

EpiPen is a common auto-injector. When using an EpiPen, the FDA advises people to:

  1. Hold the injector with one fist with the orange end facing down.
  2. Remove the blue safety release with the other hand, without bending, twisting or making lateral movements.
  3. Swing and push the orange end firmly against the outside of the thigh, at a right angle to the leg. There will be a click when the needle comes out of the orange end.
  4. Hold the needle in place for at least 3 seconds.
  5. After activation, the orange end will cover the needle and the window will be blocked. If the tip of the needle is still visible, do not reuse it.

Do not use your thumb to remove the blue safety trigger. Always use both hands to prepare the injector.

Improper removal of the safety device may result in premature release of its contents from the injector. Therefore, there may be no medication in the device when a person needs it.

The EpiPen is only one type of injector; there are many different versions. All injectors have the same effect, but the ways of using them may differ.

The links below contain instructions on how to use the different types:

Learn more about allergy medications here.

There is no way to prevent or cure an allergy, but it is possible to prevent a reaction or manage symptoms if a reaction occurs.

People at risk of an allergic reaction should:

  • Take measures to avoid exposure to known allergens.
  • Take two auto-injectors and know how to use them correctly.
  • Inform your friends, relatives, colleagues and others about the allergy and the use of the auto-injector.
  • Consider wearing a medical ID bracelet with allergy details.
  • Do allergy tests to find out which substances to avoid.

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