Allergies: What They Are, Causes, Types, Symptoms, Treatment & Relief

Allergies: What They Are, Causes, Types, Symptoms, Treatment & Relief
Adobe Stock

Allergies are a type of hypersensitivity reaction caused by the immune system. There are many types of allergies. You can be allergic to environmental allergens (like pollens and dust mites), certain medications (like antibiotics) or certain foods. 

Different types of allergies can have different symptoms. The role of an allergist is to help understand your allergy symptoms, and to determine if and how they're related to allergies.

The severity of allergy symptoms can vary by type of allergy and from person to person. For example, some people may experience mild seasonal allergies with a mild runny nose. Other people may experience more severe symptoms, including sinus congestion or worsening of their asthma.

Some people may be more prone to allergies due to their genetics. However, we don’t fully understand why some people develop allergies and some don’t. 

Types of allergies 

There are several types of allergies, which vary based on the usual triggers and the symptoms they cause. 

Seasonal/environmental allergies

The major causes of seasonal and environmental allergies include indoor and outdoor allergens. Indoor allergens include things like dust mites, cockroaches and pet dander (like cats and dogs). People can experience allergy symptoms even with “hypoallergenic” pets, as the allergen is present not just in the pet’s fur, but also in the pet’s saliva and urine. 

Outdoor allergens include pollens. The types of pollen vary by season and geographic location. In general, spring tends to have more tree pollen, summer is usually more grass pollen and fall is the peak time for weed pollen

Seasonal and environmental allergies tend to affect the sinus/nasal and respiratory systems, since the allergens are in the air and inhaled. Symptoms of seasonal and environmental allergies can include: 

  • Runny nose

  • Nasal congestion

  • Sinus pressure

  • Itchy and/or watery eyes

  • Wheezing and shortness of breath, especially in those with a history of asthma

Food allergies

Food allergies are a type of hypersensitivity reaction to certain foods. Food allergies have become more common in recent decades, especially among children

The typical symptoms of food allergy occur within a few hours of eating the food and can include:

  • Hives

  • Swelling of the lips, tongue and throat

  • Gastrointestinal upset and diarrhea

  • Nausea

  • Vomiting

  • In some severe cases, lowered blood pressure 

A severe allergic reaction involving multiple systems is called anaphylaxis

Food allergies can range in severity. Some people experience minor or local reactions. Other people may experience severe reactions, including anaphylaxis. If you have a history of a food allergy, your provider may recommend that you carry an epinephrine auto-injector, which is used to treat anaphylaxis.

Many different foods can cause food allergies. Peanuts and tree nut allergies are common, as are allergies to cow’s milk and egg. Shellfish allergy is also common, and tends to develop more frequently in adults. In some cases, you can also become allergic to mammalian meat after experiencing a tick bite (this is known as alpha-gal syndrome). 

Some food allergies persist, while others may be gradually outgrown with time. This varies by the type of allergy and by person. 

Drug allergies 

Drug allergies are a part of a spectrum of hypersensitivity reactions to medications and drugs.  There is a spectrum of hypersensitivity reactions to drugs. Some reactions occur rapidly after taking a medication (immediate-type hypersensitivity). Some other types of reactions can be delayed, occurring days or weeks after a medication is started.

The symptoms of an immediate-type drug allergy usually occur within a few hours of taking a medication, and they include: 

  • Hives

  • Swelling of the lips, face, tongue or throat

  • Difficulty breathing or wheezing

  • In some severe cases, low blood pressure

Many different types of medications can cause a drug allergy. Common causes of drug allergies include antibiotics, chemotherapy drugs and anesthetic agents. 

Other medical products, such as latex, can also cause allergy symptoms, including rash. 

Evaluating for a drug or latex allergy usually requires a consultation with an allergist, who can carefully review your history to better understand your symptoms. Depending on the drug in question and the type of reaction, your allergist may suggest allergy testing for drugs for further evaluation. 

Drug allergies can be persistent, depending on the nature of the reaction. Notably, some drug allergies can be outgrown. For example, many people with a penicillin allergy lose their sensitization to this class of medications with time. A history of a penicillin allergy can be challenging if there is a need for antibiotics in your care. If you have a penicillin allergy, seeing an allergist for further evaluation may be helpful—penicillin allergy testing may be an option to determine if you are still allergic to penicillin.   

Insect sting allergies

Allergies to insect stings involve reactions to stings from certain insects, including wasps, bees, hornets, yellow jackets and fire ants. Proteins in the venom of these species can trigger an allergic reaction.  

In general, insect sting allergy symptoms include:

  • Hives

  • Swelling

  • Difficulty breathing

  • Stomach upset

  • Sometimes low blood pressure or loss of consciousness

Anaphylaxis may be a severe allergic reaction to an insect sting. If you have experienced a severe reaction or anaphylaxis to an insect sting, your doctor may recommend that you carry an epinephrine auto-injector to treat anaphylaxis. 

If you have had an allergic reaction to a sting, it is important to consult with an allergist. Testing for venom allergy may be needed. For those who have had anaphylaxis with venom allergy, venom allergy shots (“venom immunotherapy”) can be considered to reduce the risk of anaphylaxis with future stings. 

What causes allergies?

Allergies are usually caused by having an allergic type antibody called immunoglobulin E (IgE) for certain proteins present in allergens. When the IgE antibody recognizes certain allergenic proteins, this triggers a series of immune responses that activate allergy cells and cause the release of allergic chemicals (such as histamine, leukotrienes and prostaglandins). These cells and chemicals are what cause various allergy symptoms, including hives, swelling, nasal congestion and wheezing.

Due to genetic factors, some individuals may be more likely to develop some types of allergies. 

A cold vs. allergies: How to tell the difference

A viral upper respiratory tract infection (a cold) and allergic rhinitis (allergy symptoms) can sometimes have similar symptoms, which can make it difficult to know what you are experiencing. Both a cold and allergic rhinitis can cause runny nose, sinus/nasal congestion, sneezing, cough and a scratchy throat. 

Usually, the symptoms of a cold come up suddenly and gradually resolve after about a week or so. A cold can sometimes also cause a fever. In general, symptoms of seasonal and environmental allergies tend to last longer than a week. While some people notice their allergy symptoms make them feel more tired, allergies usually don’t cause fevers. 

Allergy testing: What to expect 

An allergist can order allergy testing to help evaluate allergies. Allergists, such as those at Duke Asthma, Allergy and Airway Center, can determine the appropriate type of allergy testing based on the type of allergy symptoms you’re experiencing. 

For seasonal and environmental allergies, allergists usually test for environmental aeroallergens. These are allergens present in the air that cause allergic rhinitis and allergic asthma symptoms. These include: 

  • Pollens

  • Pet dander

  • Dust mites

  • Molds

  • Cockroach

This is usually done with “skin prick” testing. During skin prick testing, a small plastic applicator is used to gently scratch an extract of allergen onto the top layer of skin. When multiple allergens are tested at once, this can be done on the arm or on the back. It typically takes about 30 minutes for the test. The presence of a small hive or redness at the site indicates a positive test. After the test, the itching and redness usually resolves on its own in a few hours. 

For patient’s whose skin can not tolerate skin prick testing or is not appropriate, blood testing for the presence of the allergy antibody IgE can also help to identify if someone has seasonal or environmental allergies. 

For food allergies, an allergist will usually take a careful history to determine the types of food eaten and the types of symptoms experienced. This is important because there are many types of food intolerances, and food allergy testing is generally only helpful for symptoms caused by IgE-related allergies to foods. Food allergy testing is usually not helpful for nonallergic food intolerances. Testing for food allergies can be done by skin prick or via blood testing for IgE antibody to foods. 

For drug allergies, the approach to testing typically depends on the type of drug and the type of reaction. Skin testing can be helpful for immediate-type reactions to drugs. However, skin testing is not available for all medications. Additionally, for some types of reactions, such as certain delayed reactions, skin testing may not be appropriate or helpful. Your allergist can help determine if and when allergy testing for drugs and medications is appropriate for you.

Allergy relief: What treatments are available 

There are many treatments for allergies. Your allergist can help determine which treatments are most appropriate for you.

For people with seasonal and environmental allergies, medications may help to reduce allergy symptoms. Your doctor may suggest nasal sprays, which can help with nasal congestion and runny nose. These include steroid nasal sprays (such as Flonase, Nasonex, Nasacort or Rhinocort) and antihistamine nasal sprays (such as azelastine nasal spray). Oral antihistamines taken by mouth may also be helpful, such as Zyrtec, Claritin and Allegra. Your allergist can help determine which allergy medications are appropriate for you.

For those experiencing allergy symptoms despite taking medications, allergen immunotherapy (or “allergy shots”) are also an option. Allergy shots are a way to help change your immune system’s response to allergens. Allergy shots involve injections of small quantities of specific allergens in your arm. The initial phase, usually lasting a few months, typically requires weekly visits to increase your dose. After the goal dose is reached, patients usually come in monthly for maintenance shots. Because allergy shots require frequent visits, there is a significant time commitment for this therapy. However, in many patients, allergy shots can provide lasting relief from seasonal and environmental allergy symptoms.

Allergen immunotherapy is also an important treatment for those with venom allergy, called venom immunotherapy. Venom immunotherapy also involves a buildup phase with weekly shots for several months, followed by monthly shots, usually for several years. Venom immunotherapy is very effective in reducing the risk of anaphylaxis associated with future stings. Venom immunotherapy can be particularly important for those with a stinging insect allergy who have a high-risk hobby or occupation (such as those who are bee keepers or work in sanitation management).  

If you have a history of anaphylaxis, usually from food or venom allergies, your provider will likely recommend that you carry an epinephrine auto-injector at all times. The epinephrine auto-injector allows patients to self-administer epinephrine to treat anaphylaxis. 

For food allergies, there are now new treatments to help reduce the risk of anaphylaxis associated with accidental exposures to foods. Omalizumab (Xolair) was recently approved for the prevention of reactions associated with IgE-mediated food allergies. An allergist can help determine if omalizumab therapy may be helpful in reducing your food allergy risk. 

Living with allergies 

For people with seasonal and environmental allergies, it can be helpful to understand what your allergy triggers are by consulting with an allergist. Environmental modifications and lifestyle changes may be recommended, such as: 

  • Having HEPA air filters installed

  • Using dust mite-proof covers for the bed

  • Reducing upholstered surfaces

  • Reducing pet allergen exposure

For food and venom allergy, it's very important to carry the epinephrine auto-injector at all times if your doctor has prescribed it for anaphylaxis. If you have a food allergy, it's also important to make sure that you communicate your food allergy to others (particularly to people who are preparing your food). Reading food labels carefully is also key. When you’re purchasing food products, carefully look at the ingredients. In the United States, the most common food allergens (milk, eggs, nuts, fish, crustaceans, shellfish, wheat, soy and sesame) must be disclosed on the label. 

Ultimately, allergies are diverse, and vary by person. If you're concerned that you may be experiencing allergies or if you are experiencing allergy-like symptoms, talk to your primary care doctor or consult with an allergist.

Related Stories

No stories found.