Allergies

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Introduction

What are allergies?

Allergies are caused by an exaggerated response by the body’s immune system to a particular substance, called an allergen. Allergies, also called allergic reactions, are common and include food allergies, allergic conjunctivitis, respiratory allergies, insect bite allergies, drug allergies, and skin allergies. Skin allergies are linked to conditions, such as eczema and contact dermatitis. Allergies are also associated with asthma and other respiratory problems.

The immune system is made up of special cells that circulate throughout the body to defend the body against foreign substances, such as viruses and bacteria. If you have allergies, your immune system overreacts when you inhale, swallow or touch normally harmless substances, such as pollen or dust. This results in the release of powerful mediators like histamine, which causes the swelling, inflammation, and itching of affected tissues.

People with allergies are often allergic to more than one substance. Common allergies include those to dust, pollen, mold spores, animal dander, bee stings, and cockroach or dust mite droppings. Some people have allergies to certain plants; medications, such aspirin or penicillin; foods, such as eggs or milk; or chemicals and other substances, such as latex.

A very common type of allergy is hay fever, which is an allergy to pollen. Hay fever and other respiratory allergies, such as allergies to mold and dust, are types of allergic rhinitis. Symptoms of these allergies can mimic the symptoms of a cold and include runny nose and sneezing. Symptoms of other types of allergies can affect the respiratory system, the gastrointestinal system, and the skin.

Diagnosis and treatment of allergies can control symptoms of allergies to a degree that allows you to live a full and active life. Treatment may include a combination of lifestyle changes, medications and other measures.

Allergic reactions can range in severity from mild to life threatening. Seek prompt medical care if you, or your child, have symptoms of allergies, such as sneezing, watery eyes, nasal congestion, rash, or nausea and vomiting after eating certain foods.

An anaphylactic reaction is an immediately life-threatening type of allergic reaction characterized by a swollen tongue (and swelling in general), combined with hives, itching, shortness of breath, and rapid breathing (more than about 16 breaths per minute for an adult). The reaction is sudden, severe and can include respiratory distress. Seek immediate medical care (call 911) if you, or someone you are with, have symptoms of an anaphylactic reaction or other serious allergic reaction, even if there is no history of allergies.

Symptoms

What are the symptoms of allergies?

When a person has allergies, exposure to an allergen can cause a wide variety of symptoms, depending on the specific allergies, the type of exposure, and the severity of the allergies. Symptoms can occur alone or in combination with other symptoms.

Symptoms of allergies can affect the respiratory system, the skin, and the gastrointestinal system. In the most severe cases, symptoms of a type of allergic reaction called anaphylaxis can affect the cardiovascular system. Allergies are also associated with asthma and wheezing.

General symptoms of allergies

Food allergies, respiratory allergies, insect bite allergies, and skin allergies can present with a variety of symptoms that may include:

  • Itchy skin

  • Itchy, water eyes

  • Mild anxiety

  • Mild hives or swelling of a small or contained area of skin

  • Postnasal drip

  • Rash

  • Runny nose and nasal congestion

  • Sinus pressure or pain

  • Sneezing

Symptoms that might indicate a serious or life-threatening condition

Many people with asthma also have allergies. In some cases, an allergic reaction may trigger symptoms of a severe asthma attack. An anaphylactic reaction is an immediately life-threatening type of allergic reaction. An anaphylactic reaction can occur in people with no history of allergies. Seek immediate medical care (call 911) if you, or someone you are with, have any of these symptoms:

  • Change in level of consciousness or alertness, such as passing out or unresponsiveness

  • Chest pain, chest tightness, chest pressure, or palpitations

  • Difficulty breathing, shortness of breath, or wheezing (a high-pitched whistling sound made with breathing)

  • Hives or swelling that is expanding over a large area of skin

  • Inability to swallow

  • Pallor (very pale skin) or cyanosis (bluish discoloration of the lips, nails, and possibly the skin)

  • Restlessness and severe anxiety

  • Sudden swelling of the lips, tongue, mouth or face

Causes

What causes allergies?

Allergies are caused by an overreaction of the body’s immune system to a particular substance, called an allergen. The immune system is made up of special cells that circulate throughout the body to defend the body against foreign substances, such as viruses and bacteria. For people with allergies, the immune system overreacts when the person inhales, swallows or touches normally harmless substances, such as pollen, dust, and certain foods. This results in the release of powerful mediators like histamine, which causes the swelling, inflammation, and itching of tissues that are characteristic of allergies.

Allergens that cause or trigger allergic reactions vary between individuals, and almost any substance can cause an allergic reaction in a person who is allergic to that particular substance. People with allergies are often allergic to more than one substance.

Common allergens include:

  • Animal dander

  • Bee and wasp stings and other insect bites

  • Chemicals, such as latex, fragrances and preservatives

  • Cockroach and dust mite droppings

  • Dust

  • Foods, such as eggs, milk, peanuts and fish

  • Medications, such as aspirin, penicillin, and sulfa drugs

  • Metals, such as nickel, silver and copper

  • Mold spores

  • Plants, such as poison ivy and poison oak

  • Pollen

What are the risk factors for allergies?

Both genetic (inherited) and environmental factors can increase your risk of developing allergies. Not all people who are at risk for allergies will develop allergies. Risk factors include:

  • Eczema

  • Family history of allergies, especially on the maternal side

  • Lack of breast milk as an infant

  • Personal or family history of asthma

  • School-aged child

Reducing your risk of allergies

The reason your immune system overreacts to certain substances resulting in allergies is not well understood, but factors that cannot be controlled, such as genetics and a family history of allergies, play a key role in the potential to develop allergies. You may be able to reduce the risk for some types of allergies in your children by breast-feeding.

Treatments

How are allergies treated?

Allergy treatment plans use a multifaceted approach that is individualized to best address the specific cause and severity of your allergies and your age and medical history. In general, allergies are highly treatable, although they are generally not curable. Allergy treatment includes prevention of symptoms, medications to control symptoms, and lifestyle and dietary changes. Occasionally, the allergy becomes less severe as the child gets older.

Preventing allergy symptoms

Treatment of allergies begins with prevention. This includes diagnosing the specific allergen or allergens and avoiding exposure to them.

Diagnosis may include skin patch testing. In a patch test, small amounts of common allergens are applied methodically to the skin to determine what substances are triggering an allergic response. A blood test called a radioallergosorbent test (RAST) may also be done to help identify the substances that are causing certain allergies. For suspected food allergies, a patient may be asked to keep a log to record the types of foods that trigger an allergic reaction.

Once the allergens are diagnosed, you will need to avoid contact with them to prevent allergy symptoms. For example, if you have a dust allergy, you may need to "allergy proof" your home by having heating vents cleaned on a regular basis, and eliminating carpeting and draperies, which can trap and hold dust. If you have a pollen allergy, treatment may include staying in air-conditioned buildings when pollen counts are high. If you have a food allergy, you will need to read food labels and avoid the food or foods that cause symptoms.

Drug treatment of allergies

Mild to moderate respiratory and skin symptoms of allergies can be treated with a variety of over-the-counter or prescription medications available in pill, liquid, topical, and nasal spray forms. Medications that your health care provider may recommend or prescribe include:

  • Antihistamines

  • Corticosteroids

  • Cromolyn sodium

  • Decongestants

  • Leukotriene modifiers

Allergy injections may be prescribed for people who do not respond readily to oral or topical medications. For anaphylactic reactions, injectable epinephrine is generally used. Allergic asthma may also be treated with bronchodilators inhaled in a mist form.

What are the possible complications of allergies?

Complications of allergies are serious, progressive, and can even become life threatening and fatal. You can reduce the risk of serious complications or delay their development by following the treatment plan you and your health care provider design specifically for you. Complications of allergies can include:

  • Anaphylactic reaction (anaphylaxis), an immediately life-threatening type of allergic reaction

  • Asthma

  • Coma

  • Ear infections

  • Eczema

  • Lung infections

  • Multiple allergies

  • Respiratory arrest from anaphylactic shock

  • Shock

  • Sinusitis

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2018 Nov 14
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