Search Menu
Search entire library by keyword
Choose by letter to browse topics
A B C D E F G H I J K LM N O P Q R S T U V W X Y Z 0-9
(A-Z listing includes diseases, conditions, tests and procedures)

Allergy Overview

Allergies: What You Need to Know

  • An allergy is a reaction caused when the immune system mistakenly thinks a normally harmless substance is damaging to the body.

  • Allergens can be breathed or swallowed, or they can enter through the skin.

  • Allergies can affect anyone, no matter their age, gender, race or socioeconomic status.

  • To diagnose an allergy, your health care provider will give you an exam, take your medical health record and do blood and skin tests.

  • The three most effective ways to treat allergies are avoidance, allergy shots and medicine.

What are allergies?

Allergies are problems of the immune system. Most allergic reactions happen when the immune system reacts to a “false alarm.” Normally, the human body defends itself against harmful things, such as viruses or bacteria. But sometimes the immune system attacks mild things like dust, mold or pollen.

The immune system makes large amounts of the antibodies called immunoglobulin E (IgE). This is a complex chemical weapon that attacks and destroys the invading substance (i.e., dust, mold, pollen, etc.) Each IgE antibody exactly targets a specific allergen or substance that causes the allergy. In this way, inflammatory chemicals, such as histamines, cytokines and leukotrienes, are made and given off. This causes the person to experience unpleasant or even life-threatening symptoms.

What causes allergies?

Allergens are substances that can be breathed in or swallowed or that come in contact with the skin. Common allergic reactions, such as hay fever, certain types of asthma and hives, are linked to IgE. A person can be allergic to one type of pollen but not another. When a sensitive person is exposed to an allergen, the body starts making a large amount of matching IgE antibodies. When the person is exposed to the same allergen at a later point, he or she may have a reaction. Symptoms of an allergic reaction will differ based on the type and amount of allergen you have come in contact with. It also depends on how the body’s immune system reacts to that allergen.

The most common allergens are:

  • Pollen

  • Mold

  • Household dust, dust mites and dust mite waste

  • Animal dander, urine or oil from skin

  • Food

  • Medicine

  • Feathers

  • Bug stings

  • Cockroaches and their waste

  • Latex

Who is at risk for allergies?

Allergies can affect anyone, no matter their age, gender or race. Allergies are often more common in children, but a first-time event can happen at any age or come back after many years of remission.

There’s a tendency for allergies to run in families, although the exact family links that cause it aren’t yet understood. In sensitive people, things like hormones, stress, smoke, perfume or other environmental irritants may also play a role in making existing allergy symptoms worse.

Symptoms of Allergies

An allergic reaction can happen anywhere in the body. This includes the skin, eyes, lining of the stomach, nose, sinuses, throat and lungs. These are the places where immune system cells are found to fight off germs that are breathed in or swallowed or have come in contact with the skin. Often, the symptoms of allergies grow slowly over a period of time.

Allergy sufferers may become used to constant symptoms like sneezing, nasal congestion or wheezing. They may not think that their symptoms are unusual. These symptoms can often be stopped or controlled with the help of an allergist. Allergic reactions can cause:

  • A stuffy or runny nose, sneezing, itching and/or itching in the ears or roof of the mouth

  • Red, itchy, watery eyes

  • Red, itchy, dry skin

  • Hives or itchy welts

  • Itchy rash

  • Asthma symptoms, such as shortness of breath, coughing and wheezing

Latest Antidotes for Nasal Allergy Woes

Johns Hopkins allergist Dr. Sandra Lin answers questions about sublingual immunotherapy. She provides information on how it is used and the advantages of using it instead of other allergy treatments.

More Information about Sinusitis from Johns Hopkins Medicine

Dan in his home

Dan’s Story: Sinus Surgery and Sublingual Therapy

Desperate after numerous unsuccessful sinus surgeries to treat an aggressive nasal infection, Virginia-resident Dan found the Johns Hopkins Sinus Center. After sinus surgery by Dr. Andrew Lane and sublingual immunotherapy allergy treatment by Dr. Sandra Lin, Dan is now infection free and no longer taking decongestants.

Read more.

Allergy Testing

To diagnose an allergy, your health care provider will give you an exam and take your medical health record. He or she may also perform the following tests:

  • Skin test : The skin test is a way of measuring a person’s level of IgE antibodies to certain allergens. Using diluted solutions of certain allergens, the health care provider either gives you a shot with the solutions or puts them directly on the skin by making a small puncture. A raised red area on the skin of a certain size means that the person had a reaction.

  • Blood test : The blood test is used to measure the patient’s level of IgE antibodies to specific allergens. One common blood test is called radioallergosorbent test, or RAST.

Allergy Treatment

Your health care provider will figure out the best treatment for you based on:

  • Your age

  • Your overall health and medical history

  • How well you can handle specific medications, procedures or therapies

  • How long the condition is expected to last

  • Your opinion or preference

Immunotherapy is a type of treatment for allergic patients with rhinitis (hay fever), conjunctivitis or asthma. It is also used for patients with a stinging bug allergy. A mixture of the allergens the patient is allergic to is made.

  • Allergy shots are injected into the patient’s arm on a weekly basis until a maximum dose is reached.

  • Allergy drops are placed under the tongue on a daily basis until a maximum dose is reached.

Most patients get better with allergy shots or drops. It often takes six to 12 months before a clear reduction in allergy symptoms is noticed. In some patients, a reduction in symptoms is evident in as soon as six to eight months. A full course of immunotherapy is typically three to five years.

Allergy shots or drops are only part of the treatment plan for allergic patients. Since it takes time for allergy shots to become effective, you will need to stay on your allergy medication, as prescribed by your heath care provider. It is also important to keep on getting rid of allergens (such as dust mites) from your surroundings.

Medicine: There are many medicines that work well for people who suffer from allergies. Antihistamines are used to calm or stop the symptoms of allergic rhinitis (hay fever) and other allergies. Decongestants are used to treat stuffiness in the nose and other symptoms linked to colds and allergies. The use of medicines for asthma or breathing symptoms from allergies is tailored for each person based on the severity of the symptoms.

Talk with your health care provider for more information about allergy medicines.

More Information About Environmental Allergy Treatment from Johns Hopkins Medicine

Woman sneezing

Could allergy drops be the key to allergy relief?

Rather than suffer through allergy season, many people are choosing to fight back using immunotherapy, a treatment that works to boost your immune system and change the way your body responds to allergens. This treatment involves gradually introducing small amounts of what you’re allergic to.

Learn more.

What are the complications of allergies?

Anaphylactic shock or anaphylaxis can happen in extreme cases. Anaphylaxis is a serious, life-threatening reaction to certain allergens. Body tissues may swell, including tissues in the throat. Anaphylaxis can also cause a sudden drop in blood pressure. Although each person may feel symptoms differently, these are the most common symptoms of anaphylaxis:

  • Itching and hives over most of the body

  • Swelling of the throat and tongue

  • Difficulty breathing

  • Dizziness

  • Headache

  • Stomach cramps, nausea or diarrhea

  • Shock

  • Loss of consciousness

Anaphylaxis can be caused by an allergic reaction to a drug, food, serum, bug venom or allergen extract. Some people who are aware of their allergic reactions or allergens carry epinephrine to counteract severe allergic reactions.

More Information About Environmental Allergies from Johns Hopkins Medicine

Man sneezing

Allergies: Answers from Allergy Expert Dr. Sandra Lin

About 45 million Americans suffer from environmental allergies. Dr. Sandra Lin, a Johns Hopkins otolaryngologist (ENT) and allergy expert, answers some of the most commonly asked questions about treating environmental allergies.

Learn more.

Living with Allergies

Avoidance is a very effective way to treat allergies. Ideas for avoiding allergens are:

  • Staying indoors when the pollen count is high and on windy days

  • Dust-proofing your home, particularly the bedroom:

  • When possible, get rid of carpeting, Venetian blinds, down-filled blankets or pillows and unused clothes.

  • Wash bedding, curtains and clothing often and in hot water to get rid of dust mites.

  • Keep bedding in dust covers when possible.

  • Using air conditioning instead of opening windows

  • Putting a dehumidifier in damp parts of the home (remember to clean it often)

  • Wearing a face mask when working in the yard

  • Choosing a vacation by the beach during the heaviest part of the pollen season

Your health care provider will also have suggestions for avoiding allergens that cause reactions.

For information about food allergies please visit the following pages:

More Information About Environmental Allergies in the Health Library

Find a physician at another Johns Hopkins Member Hospital:
Connect with a Treatment Center:
Find Additional Treatment Centers at: