Allergies are hypersensitive responses from the immune system to substances that either enter or come into contact with the body.

These substances commonly include materials such as pet dander, pollen, or bee venom. Anything can be an allergen if the immune system has an adverse reaction.

A substance that causes an allergic reaction is called an allergen. Allergens can be found in food, drinks, or the environment.

Many allergens are harmless and do not affect most people.

If a person is allergic to a substance, such as pollen, their immune system reacts to the substance as if it was foreign and harmful, and tries to destroy it.

Research indicates that 30 percent of adults and 40 percent of children in the United States have allergies.

Fast facts on allergies

  • Allergies are the result of an inappropriate immune response to a normally harmless substance.
  • Some of the most common allergens are dust, pollen, and nuts. They can cause sneezing, peeling skin, and vomiting.
  • Anaphylaxis is a serious allergic reaction that can be life-threatening.
  • To diagnose an allergy, a clinician may take a blood sample.
  • The symptoms of an allergy can be treated with drugs. However, the allergy itself requires desensitization.
  • Anaphylaxis requires emergency treatment. Epinephrine injectors can help reduce the severity of an anaphylactic reaction.

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Allergies occur when the immune system overreacts to ordinarily harmless substances.

Allergies are a very common overreaction of the immune system to usually harmless substances.

When a person with an allergy comes into contact with an allergen, the allergic reaction is not immediate. The immune system gradually builds up sensitivity to the substance before overreacting.

The immune system needs time to recognize and remember the allergen. As it becomes sensitive to the substance, the immune system starts making antibodies to attack it. This process is called sensitization.

Sensitization can take a few days or several years. In many cases, the sensitization process is not completed. The patient experiences some symptoms but not a full allergy.

Allergies may also be seasonal. For example, hay fever symptoms can peak between April and May, as the pollen count in the air is much higher.

A study published in JAMA Pediatrics reported that food allergies in children cost the U.S. economy nearly $25 billion annually.

The number of people worldwide with allergies is increasing.

An allergic reaction causes inflammation and irritation. The signs and symptoms depend on the type of allergen. Allergic reactions may occur in the gut, skin, sinuses, airways, eyes, and nasal passages.

Allergic reactions may be confused for other conditions. Hay fever, for example, creates similar irritations to the common cold but the causes are different.

Below is a range of various triggers and the symptoms they regularly cause in people who are allergic.

Dust and pollen

  • blocked nose
  • itchy eyes and nose
  • runny nose
  • swollen and watery eyes
  • cough

Skin reactions

  • flaking
  • itching
  • peeling
  • rashes

Food

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

Insect stings

  • wheezing
  • swelling at the site of the sting
  • a sudden drop in blood pressure
  • itchy skin
  • shortness of breath
  • restlessness
  • hives, a red and very itchy rash that spreads across the body
  • dizziness
  • cough
  • chest tightness
  • anxiety
  • possible anaphylaxis

Medication:

  • wheezing
  • swollen tongue, lips, and face
  • skin rash
  • itchiness
  • possible anaphylaxis

Anaphylaxis

Anaphylaxis is a quickly escalating, serious allergic reaction that sets in rapidly. It can be life-threatening and must be treated as a medical emergency.

This type of allergic reaction presents several different symptoms that can appear minutes or hours after exposure to the allergen. If the exposure is intravenous, onset is usually between 5 to 30 minutes. A food allergen will take longer to trigger anaphylactic reaction.

Researchers reported in The Journal of Allergy & Clinical Immunology that the most commonly affected areas in anaphylaxis are the skin and respiratory system.

Symptoms of anaphylaxis include:

  • hives all over the body, flushing, and itchiness
  • swollen tissues
  • a burning sensation
  • swelling of the tongue and throat.
  • a possible blue tint to the skin from lack of oxygen
  • a runny nose
  • shortness of breath and wheezing
  • hoarseness
  • pain when swallowing
  • cough
  • a drop in blood pressure that can speed up or slow down the heart rate
  • abdominal cramps
  • diarrhea
  • vomiting
  • loss of bladder control
  • pelvic pain similar to uterine cramps
  • coronary artery spasm
  • low blood pressure leading to high or low heart rate
  • dizziness and fainting

Recognizing these symptoms can be crucial to receiving timely treatment.

A particular antibody called immunoglobin (IgE) causes allergic reactions. Antibodies are released to combat foreign and potentially harmful substances in the body.

IgE is released to destroy the allergen and causes the production of chemicals that trigger the allergic reaction.

One of these chemicals is called histamine. Histamine causes tightening of the muscles in the airways and the walls of blood vessels. It also instructs the lining of the nose to produce more mucus.

Risk factors

The following can be risk factors for developing allergies:

The most common allergens

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Animal dander is a very common allergen.

Potential allergens can appear almost anywhere.

Any food can theoretically cause an allergy. Specific components of food can also trigger allergic reactions, such as gluten, the protein found in wheat. The eight foods most likely to cause allergies are:

  • eggs, especially egg-white
  • fish
  • milk
  • nuts from trees
  • peanuts
  • wheat
  • soy
  • shellfish

Other allergens include:

  • animal materials, such as dust mite excrement, wool, fur, dander, or skin flakes, as well as Fel d 1, a protein found in cat saliva
  • medications, such as penicillin, salicylates, and sulfonamides
  • foods such as corn, celery, pumpkin, sesame, and beans
  • insect stings, including wasp and bee sting venom, mosquito stings, and fire ants.
  • insect bites from horseflies, blackflies, fleas, and kissing bugs
  • cockroaches, caddis and lake flies, midges, and moths
  • plant pollens from grass, trees, and weeds
  • household chemicals
  • metals, such as nickel, cobalt, chromium, and zinc
  • latex

The doctor will ask the patient questions regarding symptoms, when they occur, how often, and what seems to cause them. They will also ask the person with symptoms whether there is a family history of allergies, and if other household members have allergies.

The doctor will either recommend some tests to find out which allergen is causing symptoms or refer the patient to a specialist.

Below are some examples of allergy tests:

  • Blood test: This measures the level of IgE antibodies released by the immune system. This test is sometimes called the radioallergosorbent test (RAST)
  • Skin prick test: This is also known as puncture testing or prick testing. The skin is pricked with a small amount of a possible allergen. If the skin reacts and becomes itchy, red, and swollen, it may mean an allergy is present.
  • Patch test: A patch test can identify eczema. Special metal discs with very small amounts of a suspected allergen are taped onto the individual's back. The doctor checks for a skin reaction 48 hours later, and then again after a couple of days.

The American College of Allergy, Asthma and Immunology can help you find a certified allergist.

Even if the patient knows what triggers the allergy, the doctor will carry out tests to determine which particular substance is causing symptoms.

The most effective treatment and management of an allergy is avoidance of the allergen.

However, sometimes it is not possible to completely avoid an allergen. Pollen, for example, is constantly floating in the air, especially during hay fever season.

Medications

Drugs can help treat the symptoms of an allergic reaction, but they will not cure the allergy. The majority of allergy medications are over-the-counter (OTC). Before taking a particular type of medication, speak to a pharmacist or doctor.

  • Antihistamines: These block the action of histamine. Caution is recommended, as some antihistamines are not suitable for children.
  • Decongestants: These can help with a blocked nose in cases of hay fever, pet allergy, or dust allergy. Decongestants are short-term medications.
  • Leukotriene receptor antagonists, or anti-leukotrienes: When other asthma treatments have not worked, anti-leukotrienes can block the effects of leukotrienes. These are the chemicals that cause swelling. The body releases leukotrienes during an allergic reaction.
  • Steroid sprays: Applied to the inside lining of the nose, corticosteroid sprays help reduce nasal congestion.

Immunotherapy

Immunotherapy is also known as hyposensitization. This type of therapy rehabilitates the immune system. The doctor administers gradually increasing doses of allergens over a period of years.

The aim is to induce long-term tolerance by reducing the tendency of the allergen to trigger IgE production.

Immunotherapy is only used to treat severe allergies.

Treatment for anaphylaxis

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The EpiPen is one example of an epinephrine injector. They can be vital for stopping anaphylactic reactions.

Anaphylaxis is a medical emergency. The patient may require resuscitation, including airway management, supplemental oxygen, intravenous fluids, and close monitoring.

The person experiencing anaphylaxis will need an injection of adrenaline into the muscle. Antihistamines and steroids are often used alongside the adrenaline injection.

After the patient has been stabilized, doctors may recommend remaining in hospital under observation for up to 24 hours to rule out biphasic anaphylaxis. Biphasic anaphylaxis is the recurrence of anaphylaxis within 72 hours with no further exposure to the allergen.

Patients who have had severe allergic reactions should carry an epinephrine autoinjector with them, such as the EpiPen, EpiPen Jr, Twinject, or Anapen.

Many doctors and health authorities advise patients to wear a medical information bracelet or necklace with information about their condition.

How to prevent allergies

There is no way to prevent an allergy. However, it is possible to limit symptoms.

Even though treatments can help alleviate allergy symptoms, patients will need to try to avoid exposure to specific allergens. In some cases, this is not easy. Avoiding pollen in late spring and summer is virtually impossible, and even the cleanest houses have fungal spores or dust mites.

If you have friends or family with pets, avoiding them might be difficult. Food allergies can be challenging to manage because traces of allergens can appear in unlikely meals. However, being vigilant about checking food packages can be a key way to avoid consuming certain allergens.

Make sure you receive proper allergy testing and know what substances to avoid.