Allergy is the immune-response to a foreign substance known as allergen. Allergy is described as a hypersensitivity reaction, an inappropriate immune response to typically harmless substances.

Allergy: Overview

Allergy is a broad topic and speaks to the body’s immune response to foreign substances, known as allergens. This response is described as a hypersensitivity reaction, an inappropriate immune response to typically harmless substances.


When your immune system comes into contact with an allergen, it forms antibodies against it. These will act as a sort of “memory” for your immune system, remembering it as a harmful substance the next time you come into contact with it so it can act quicker and stronger. Reactions develop within a few minutes to approximately two hours after exposure.

When you come into contact with the allergen, these antibodies travel to specific cells that release histamine and other chemicals, which causes inflammation. The response can vary from a minor inconvenience like atopic dermatitis and rhinitis to a severe manifestation like anaphylaxis — a life-threatening emergency.

What Is the ICD 10 Code for Allergies?

The ICD / ICD 10 code for Allergies is "T78.40XA" (Allergy, unspecified, initial encounter).

Allergy: Symptoms

An allergic reaction typically triggers symptoms in the digestive system, skin, airways, sinuses, and nasal passages. Symptoms will vary depending on the cause and the affected area; they can include:

  • A runny nose or sneezing
  • Flushing
  • Coughing, wheezing, or shortness of breath
  • Itchy skin or hives
  • Diarrhea
  • Nausea and vomiting
  • Swollen lips, tongue, and airway
  • Abdominal cramping

Symptoms of Anaphylaxis

Signs and symptoms of anaphylaxis include:

  • Loss of consciousness
  • A drop in blood pressure
  • Shortness of breath
  • Rash
  • Lightheadedness
  • A rapid, weak pulse
  • Nausea and vomiting

Allergy: Causes

An allergy starts when your immune system mistakes a harmless substance for a harmful one and produces antibodies against it. When exposed to the allergen again, these antibodies can trigger the release of several chemicals, such as histamine, that cause allergy symptoms. Some of the most common allergens include:

  • Tree and grass pollen
  • Foods such as peanuts and eggs
  • Animals, particularly dog or cat saliva and dander
  • Insect stings
  • Certain drugs

Allergy: Diagnosis

Your doctor, ideally an allergy specialist, will do a physical exam and take a medical history for which they’ll ask you a series of questions, including but not limited to the following:

  • What symptoms you’re experiencing, and how often
  • When your symptoms began
  • If you ingested anything or made any new changes
  • Prior history of allergic reactions
  • History of allergic rhinitis (hay fever), asthma, or eczema

Allergy testing

Adults and children of any age can be tested for allergies. Both blood and skin allergy tests can detect a patient’s sensitivity to different allergens. Skin testing is the preferred method and is usually the most accurate. Blood tests may be ordered in specific situations.

During skin tests, your skin is exposed to different allergens and is then observed for signs of an allergic reaction. Different types of skin tests are available. A skin prick or scratch test is done using a needle to penetrate the skin’s surface slightly, making several marks and placing a tiny drop of allergen extracts in each one. After 15 minutes, the healthcare provider observes your skin for signs of an allergic reaction. A skin injection or intradermal test uses a needle to inject a small amount of allergen extract into your skin. The skin is examined after 15 minutes to check for signs of an allergic reaction. This test is commonly used to check for penicillin or insect venom allergy. And a patch test is done to see if an allergen is causing skin inflammation. This test can detect delayed allergic reactions that can take several days to develop. For this test, allergens are applied to patches, which are then placed on your skin, you wear them for 48 hours, and then the patches are removed. Irritated skin at the site where the patch was might indicate an allergy.

Blood testing can also be done, but it takes a long time to get the results, and they’re more expensive. There are many types of allergy blood tests, and some are more helpful than others.

A doctor might advise against skin testing if you have had a severe allergic reaction, take medications that interfere with the results, or have certain skin conditions that make it difficult or impossible to perform the test. Some blood tests could be helpful for patients who can’t undergo skin tests.

Skin and blood tests alone are not enough to diagnose an allergy. It must be done with a thorough medical history, ideally by an allergy specialist.

Allergies: Treatment

Allergy treatments include:

  • Allergen avoidance. Identifying and avoiding what triggers your allergies is a crucial first step.
  • Medications. Antihistamines and decongestants are the most common allergy medications. Corticosteroids are also occasionally prescribed.
  • Immunotherapy. Immunotherapy is a preventive treatment for allergic reactions. It involves gradually increasing doses of the allergen to which you’re allergic. The incremental increases in the allergen cause the immune system to become less sensitive to the allergen. There are allergy shots (also known as subcutaneous immunotherapy) and sublingual (under the tongue) immunotherapy.
  • Emergency epinephrine. For a severe allergic reaction like anaphylaxis, an epinephrine shot (Auvi-Q, EpiPen, others) can reduce symptoms until you get emergency treatment.

Types of Allergies

Several types of allergies and allergens that can trigger them exist. The following includes some, but not all, of the most common types and triggers.

Respiratory Allergies

Respiratory allergies are very common and can occur at any age. Allergic asthma and allergic rhinitis (also known as hay fever or seasonal allergies) are the two types of respiratory allergies.

Many people first get allergic rhinitis when they are children or young adults, and are lifelong. Symptoms can improve or worsen over time. Some people have symptoms seasonally, but some have symptoms last all year. Year-round symptoms are usually caused by:

  • Insects, such as dust mites and cockroaches
  • Animals, such as cats and dogs
  • Mold spores

Allergic Rhinitis Symptoms

Symptoms of allergic rhinitis include:

  • Sneezing
  • Runny, stuffy, or itchy nose
  • Watery, red, itchy, or swollen eyes

Seasonal Allergies

Seasonal allergies can be prevented if the timing of your symptoms is predictable. Some people can prevent the symptoms by starting their medicine a week or two before the time of the year that they usually get them.

Other prevention methods include staying inside during the times of the year when you have symptoms, keeping the car and house windows closed, taking a shower before bed to rinse pollen off hair and skin, and wearing a dust mask when being outside.

Allergic asthma is a type of asthma in which exposure to an allergen causes the bronchi (airways) to constrict and trigger wheezing, coughing, and other classic asthma symptoms.

Food Allergies

Eight types of food cause 90% of allergic reactions: eggs, milk and dairy, peanuts, tree nuts, fish, shellfish, wheat, soy, and sesame. They can develop at any age, but most will appear in early childhood.

Most symptoms occur within two hours of ingestion and often start within minutes. In rare cases, the reaction may be delayed by four to six hours or longer. A food allergy can cause:

  • Tingling in the mouth
  • Swelling of the tongue
  • Pale or blue coloring of the skin
  • Hives
  • Anaphylaxis
  • Itching
  • Nausea and vomiting
  • Stomach cramps
  • Shortness of breath or wheezing
  • Repetitive cough

Skin Allergies

Contact dermatitis is a reaction that appears when the skin comes in contact with an irritant – a substance that directly damages the outer layer of skin – or an allergen. This reaction usually occurs within a few hours or days of exposure. Symptoms include a rash, blisters, itching, and burning. Nickel is used in jewelry and is a common cause of contact dermatitis. Other things that can cause contact dermatitis include soaps, laundry detergents, fabric softeners, shampoos, adhesives, nail polish, topical medications, plants (like poison ivy, oak, and sumac, all of which contain urushiol), and latex gloves.

The ideal solution is to avoid contact with the irritants or allergens that trigger your symptoms, and your skin will eventually clear up. However, if this is impossible or your skin doesn’t clear up on its own, you may also be advised to use emollients such as petrolatum ointment or topical corticosteroids.

Drug Allergies

A drug allergy is a bad reaction to a drug or medicine. Like in other types of allergies, the immune system responds to a drug as if it were harmful and tries to fight it off. A drug allergy is not the same as a drug side effect.

There are a few different types of drug allergies. One type of allergy is called an "immediate" allergy because it starts quickly after taking a drug (usually within an hour). It usually happens with drugs a person has taken before without any problem. Symptoms can include hives, itchy skin, flushing, swelling of the face, hands, feet, or throat, throat tightness, hoarse voice, wheezing, trouble breathing, nausea, vomiting, belly pain, and feeling lightheaded. If you keep taking the drug, this type of allergy can become anaphylaxis.

Another type of drug allergy, called a "delayed" allergy, is much more common. It causes a rash that begins after a few days of taking a drug. Sometimes it is itchy, but not always, and it doesn’t involve the same symptoms as the “immediate” type of drug allergy, such as swelling and trouble breathing.


Dr. Erika RM Von Mutius: KOL #1 for Allergies

According to KOL's technology, Dr. Erika RM von Mutius is the top ranking Key Opinion Leader (worldwide) for Allergies. You can see Dr. Erika RM von Mutius's KOL resume and other concepts for which they rank #1 worldwide.

Erika RM von Mutius
Helmholtz Zentrum München, Institute of Environmental Medicine (IEM), Neusässer Straße 47, 86156 Augsburg, Germany
KOL #1 (worldwide) for: Allergies

Erika von Mutius completed her internship and residency training in the Department of General Pediatrics, Neonatal and Pediatric Intensive Care at the Dr. von Hauner Children’s Hospital at LMU Munich. After her residency, she spent a year as a research fellow at the University of Arizona, Respiratory Science Center, with Professor Fernando Martinez, where she caught fire for science.

She added a Master of Science Degree in Epidemiology at Harvard School of Public Health to her medical training. As a senior physician and professor of pediatric allergology and pneumology, Erika von Mutius heads the Department of Asthma and Allergy at the Dr. von Hauner Children’s Hospital and, since 2017, also the Institute of Asthma and Allergy Prevention at Helmholtz Munich.

Under Erika von Mutius leadership, numerous interdisciplinary, multicenter population-based studies have investigated the role of genetic and environmental risk and protective factors for childhood asthma and allergic diseases, both nationally and internationally. The most prominent studies are the so-called farm studies in which she and her team unravel the relevant exposures and underlying mechanisms conferring such strong protection from asthma and allergies. Erika von Mutius is furthermore Member of the Board of Directors of the German Centre for Lung Research (DZL), Director of the Munich site (CPC-M) of the DZL and coordinator of the Disease Area Asthma & Allergy within DZL.

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