Allergy

What Are Allergies?

Millions of people are affected by allergies, affecting approximately 20-30% of the population according to the American Academy of Allergy, Asthma & Immunology (Opens in a new window). The likelihood of developing allergies or allergic reactions is genetically inherited, meaning allergies often run in families. If you have a personal or family history of allergies and are exposed to certain things, called allergens, in your environment, you may become allergic to some of those substances.

When you have a repeat exposure to one of these substances (through breathing or touching), you may have an allergic reaction which can involve:

• Itching
• Nasal congestion
• Swelling
• Other symptoms

Allergic reactions vary widely in severity from person to person and can also be affected by seasonal and environmental factors.

Most allergies cannot be cured completely, but symptoms can be well controlled. Some children outgrow certain allergies, while environmental and seasonal allergies often persist without treatment

Types

Allergic conditions and allergic reactions occur when the immune system misidentifies harmless foreign substances — called allergens (Opens in a new window) — and reacts to them as if they were harmful. Allergic conditions include:

• Allergic rhinitis
• Allergic asthma
• Anaphylaxis
• Food allergy
• Medication allergy
• Venom allergy

Causes

Allergies and allergic reactions occur when the immune system reacts to nonharmful allergens. Allergies develop when your immune system produce antibodies called IgE that are specific to that allergen. Upon subsequent encounters with the same allergen, the allergen binds to those IgE antibodies on immune cells called mast cells. This triggers the release of histamine and other chemicals, causing allergy symptoms. Risk factors to developing allergies include family history, having eczema, environmental factors such as aur pollution, urban living, preterm birth, etc. While most allergies begin in early childhood, they can develop at any time.

Allergen Exposure

Some people are allergic to many substances. Others are allergic to a few. A person’s allergy is determined by many different factors, including the environment, a person's genes and the way their immune system works.

Common Allergens

• Animals
• Cockroaches
• Dust mites
• Foods
• Insect stings
• Latex
• Medication/drugs
• Mold
• Pollen

At least two exposures to an allergen are required: the primary exposure and the secondary exposure.

Primary Exposure

An allergen, such as mold spores or pollen, enters the body through the mouth or nose or lands on the skin. In a person with allergies, white blood cells (T cells) identify the allergen as foreign and release chemicals in response. These chemicals travel through the blood and instruct another kind of white blood cell (B cells) to produce IgE antibodies. Some of these IgE antibodies attach to the outside of another special type of white blood cell called a mast cell. Mast cells are scattered throughout the skin and respiratory tract. Their purpose is to help mediate the inflammatory response of the immune system. IgE antibodies can remain attached to mast cells for many years.

Secondary Exposure

When the same allergen is encountered again, it binds directly to the IgE antibody attached to the outside of mast cells. This causes the mast cells to become activated and release chemicals, such as histamine. Histamine is an example of a chemical mediator — a special "messenger" chemical that immune cells use to talk to each other.

Histamine is one of the best-known mediators. It is responsible for causing many of the symptoms associated with allergies. Histamine opens small blood vessels, causing them to leak fluid. This results in inflammation: warming and swelling of the skin, itching and watery eyes. Histamine causes sneezing and increased mucus production in the nasal cavity and airways that leads to runny nose, postnasal drip and cough.

Signs and Symptoms

The severity and kinds of allergy symptoms depend on a person's genetics, the allergic condition and the type and amount of allergens involved.

The most common allergy symptoms affect the nose, sinuses, lungs and eyes. However, in some conditions, organs such as the skin, digestive system and blood vessels can be affected as well.

Not all allergic reactions happen the same way. Some allergy symptoms occur immediately after exposure to an allergen, while others take hours or days to occur.

Common Allergy Symptoms

• Cough
• Itchy nose, mouth, or throat
• Itchy or watery eyes
• Itchy, red, or irritated skin (eczema)
• Postnasal drip
• Runny or stuffy nose
• Severe reactions such as trouble breathing, throat tightness, or dizziness (signs of anaphylaxis)
• Skin rashes or hives
• Sneezing
• Stomach pain, nausea, or vomiting (more common with food allergies)
• Swelling of the lips, eyes, or face
• Vomiting
• Wheezing or shortness of breath

Immediate Allergic Reactions

Immediate allergic reactions typically occur within minutes of exposure to an allergen. Allergic reaction time will vary depending on a person's genetics and on the site of the body affected.

Delayed or Late-Phase Allergic Reactions

Delayed or late-phase allergic reactions generally occur 2–6 hours after exposure (and even longer in some people). Signs and symptoms of delayed or late-phase allergic reactions are generally the same as those for immediate allergic reactions.

In the case of allergic asthma, a delayed allergic reaction can cause other problems, such as loss of sleep due to nighttime asthma attacks. There are ways to time allergy and asthma medications to reduce symptoms of a delayed allergic response.

Anaphylaxis

Anaphylaxis is a severe, life-threatening allergic reaction that requires immediate medical care.

Signs of anaphylaxis may include:

• Dizziness or fainting
• Hives over large areas of the body
• Rapid heartbeat
• Swelling of the lips, tongue, or throat
• Trouble breathing
• Vomiting or diarrhea

Use epinephrine right away if you suspect anaphylaxis, then call 911. People with a history of anaphylaxis should carry an epinephrine auto-injector at all times.

Diagnosis

To diagnose allergies, or allergic disease, allergists evaluate a person’s clinical history and family history. They also perform a physical examination, skin tests and laboratory tests. These tests serve to confirm the diagnosis of allergic disease and to identify potential allergic triggers, knowledge that is useful to guide allergen avoidance strategies. Because allergy symptoms can overlap with asthma, infections, food intolerances and other conditions, evaluation by a board-certified allergist helps ensure the diagnosis is accurate and the test results are interpreted correctly.

Allergy Tests

Skin Prick Testing

Skin prick tests help identify sensitivities to pollen, mold, dust mites, animals, insect stings, and certain foods. A small amount of allergen is placed on the skin, which is then gently pricked. A raised, itchy bump indicates a possible allergy.

Skin Intradermal testing

Intradermal testing is a form of allergy skin testing in which a small volume of diluted allergen is injected into the dermis using a fine needle, typically on the forearm. It is primarily used as a second-line test when skin prick testing is negative but clinical suspicion for allergic sensitization remains high.

Specific IgE Blood Testing

Blood tests measure IgE antibodies to specific allergens. These may be used if skin testing is not possible—such as in the presence of severe eczema, certain medications, or higher risk of reaction.

Treatment

Allergy symptoms can be successfully relieved through a combination of allergen avoidance and allergy treatment options, including allergy medications and immunotherapy.

The primary strategy of treating allergies is the careful identification of what a person is allergic to and staying away from those things. If that is not possible, medications are used to treat the symptoms of allergy. Additionally, immunotherapy is used to control symptoms of moderate to severe allergies if avoidance and medications are not working.

Medications

Many medications are available to treat the various allergy symptoms.

Antihistamines

Antihistamines are often the first medications used to treat allergy symptoms because they directly block the effects of histamine — the chemical responsible for itching, sneezing, watery eyes, and runny nose. These medications can be taken by mouth or used in nasal sprays and eye drops. Modern, non-sedating antihistamines tend to cause less drowsiness and are safe for long-term use when taken as directed. Antihistamines help control day-to-day symptoms, but they work best when taken before or at the earliest sign of an allergic response.

Anti-IgE Therapy (Biologics)

Anti-IgE therapy is a type of biologic treatment reserved for people with severe allergic asthma or difficult-to-control environmental allergies. This therapy works by targeting IgE — the antibody involved in allergic reactions — and preventing it from triggering inflammation in the lungs and airways. Anti-IgE treatment is given as regular injections under medical supervision. For individuals who qualify, biologics can significantly reduce asthma flare-ups, improve breathing, and lessen the need for oral steroids. Your allergy specialist can determine whether biologic therapy is appropriate based on your symptoms, test results, and overall treatment response.

Immunotherapy

Allergy shots

Subcutaneous immunotherapy (commonly called allergy shots) is a form of treatment to reduce an allergic reaction to allergens. Allergy shots consist of a series of injections (shots) with a solution containing the allergens that cause your symptoms. There are usually two phases: buildup and maintenance. Treatment buildup begins with a weak solution given once or twice a week. The strength of the solution is gradually increased with each dose. Once the strongest dosage is reached in a few months, the injections are slowly spaced apart until they reach a frequency of once a month. At that point, sensitivity to the allergens has been decreased and a person has reached a maintenance level. Monthly doses are recommended to continue for at least 3-5 years.

Though not a cure for everyone, allergy shots can significantly reduce allergy symptoms in people who are unable to avoid allergens and who do not respond well to other medications.

Allergy shots should always be given at your health care provider's office since there is a risk of a severe reaction.

Research has shown that allergy shots can reduce symptoms of:

• Allergic rhinitis (hay fever)
• Allergic asthma
• Animal dander allergy
• Dust mites allergy
• Grass, weed and tree pollen allergies
• Insect sting allergy

Allergy shots are less effective against molds and are not a useful method for the treatment of food allergies.

Six months to a year of allergy shots may be required before you notice any improvement in symptoms. If your symptoms do not improve after this time, ask you allergist to review your overall treatment program. In general, allergy shots should be stopped if they are not effective within 2-3 years.

If the treatment is effective, the shots often continue for at least 3-5 years, until the person is symptom-free or until symptoms can be controlled with mild medications. After stopping, some individuals may have a return of symptoms. You should discuss this with your allergist to design an individual treatment program that optimizes your goals.

"Rush Immunotherapy"

"Rush immunotherapy" is a series of allergy shots given over 2-3 consecutive days. This "rushes" the initial buildup phase of the treatment. Increasing doses of allergen extract are given every 30 minutes to hourly instead of every few days or weeks. There is an increased risk of a reaction with this procedure. Therefore, rush immunotherapy should only be done in a hospital or high-risk procedure area under very close supervision.

Immunotherapy Without Injections

Sublingual immunotherapy is a treatment method to treat allergies without injections. Small doses of allergens are introduced under the tongue to reduce allergic symptoms. Currently, the U.S. Food and Drug Administration (FDA) has approved only four sublingual products. Two are directed at different kinds of grass pollen, one is for short ragweed, and one is for house dust mite. The two grass pollen allergy tablets are: Oralair® (Stallergenes), which applies to five kinds of northern grass pollen, and Grastek® (ALK), which applies to Timothy Grass pollen. The short ragweed allergy tablet is called Ragwitek® (ALK). The house dust mite tablet is called Odactra® (ALK).

Leukotriene Modifiers

Leukotriene modifiers help block chemicals called leukotrienes, which contribute to inflammation in the airways. These medications are often used for people who have both allergic rhinitis and asthma, since they can help reduce wheezing, nighttime symptoms, coughing, and congestion. They are taken orally once daily and may be used alone or in combination with other allergy medications. Leukotriene modifiers are especially helpful when allergies trigger asthma symptoms or when nasal sprays and antihistamines do not provide enough relief.

Nasal Corticosteroids

Nasal corticosteroid sprays are considered one of the most effective treatments for allergic rhinitis. They reduce swelling and inflammation inside the nasal passages, helping relieve congestion, runny nose, postnasal drip, and sinus pressure. These sprays work gradually, so consistent daily use is important. While nasal corticosteroids are generally safe, they should be used at the lowest dose needed to control symptoms. With regular use, many patients experience fewer flare-ups and better overall control of seasonal or year-round allergies.

Topical Steroids

Topical steroids, available as creams, ointments, or lotions, are commonly used to treat allergic skin conditions. These medications reduce redness, swelling, and itching by calming inflammation directly at the affected area. Different strengths are available, and your doctor will help select the right formulation for the part of the body being treated. When used as directed, topical steroids are safe and effective, although long-term use on sensitive areas may require special guidance from a clinician.

Lifestyle Management

Lifestyle changes play a key role in managing allergies and reducing day-to-day symptoms. While medications and immunotherapy can be very effective, avoiding triggers and improving your home and work environments often provides additional relief. The prevention strategies below can help reduce exposure to common allergens, support long-term symptom control, and complement the treatment plan recommended by your allergist.

Control Dust Mites

Dust mites thrive in warm, humid environments and often trigger year-round allergy symptoms. Prevention focuses on minimizing mite exposure in the bedroom, where most contact occurs. This can include using allergen-proof covers for mattresses and pillows, washing bedding weekly in hot water, vacuuming with a HEPA-filter vacuum, and reducing indoor humidity to below 50%. Removing heavy curtains, stuffed animals, or thick carpets in the bedroom may also help.

Avoid Tobacco Smoke

Tobacco smoke can worsen allergy symptoms and increase irritation of the airway and nasal passages. Avoiding exposure to both active smoking and secondhand smoke is an important part of managing symptoms, especially for children.

Watch for Mold

Mold grows in damp areas such as bathrooms, kitchens, basements, and around leaky pipes. Reducing moisture is the most important prevention step. Use exhaust fans in bathrooms and kitchens, fix plumbing leaks promptly, clean visible mold with appropriate solutions, and consider a dehumidifier in humid spaces. Keeping indoor humidity below 50% can slow mold growth.

Prevent Insect Stings

People with stinging insect allergies must take extra precautions outdoors. Prevention includes wearing closed-toe shoes, avoiding sweet foods or drinks outside, keeping trash cans covered, and not wearing strong fragrances that attract insects. If you have a history of severe reactions, carry epinephrine with you at all times and review your action plan with your clinician.

Avoid Pet Allergens

Proteins found in a pet’s dander, saliva, and urine can cause allergies. While avoiding exposure is most effective, many people choose to live with pets and need ways to limit allergens. Strategies include keeping pets out of the bedroom, using HEPA air cleaners, bathing and grooming pets regularly, and cleaning floors, furniture, and bedding often. Discuss with your allergist whether additional medications or immunotherapy might help if symptoms remain uncontrolled.

Reduce your Exposure to Pollen

Pollen from trees, grasses, and weeds is one of the most common triggers of seasonal allergies. Symptoms often worsen outdoors on dry, windy days or during high-pollen seasons. You can reduce exposure by keeping windows closed, using air conditioning, and checking local pollen forecasts. Showering after outdoor activities and using a HEPA filter inside your home can also help remove pollen from skin, hair, and indoor air.

Clinical Trials

Clinical trials help determine new treatment options for diseases and conditions. Patients with allergies have access to clinical trials and should speak with their physician to determine what trials might work best for them.

When to See a Specialist

It’s important to be evaluated by a board-certified allergist if you or a loved one:

• Has allergy symptoms
• Would like to improve your current treatment of allergies

At National Jewish Health in Denver, Colorado, we treat thousands of adults and children with allergies each year. Learn about our adult allergy treatment program and our pediatric allergy treatment program or use the button below to make an appointment.