Allergies and anaphylaxis

Your body's immune system protects you from harmful substances, such as viruses and bacteria. Sometimes, the immune system develops an exaggerated reaction to a particular substance. This is an allergic reaction. These reactions can vary from a minor irritation to a generalized life-threatening reaction known as anaphylaxis.


The immune system
An allergic reaction is the result of several events occurring within the immune system. Substances that trigger allergic reactions -- such as pollen, mold and animal dander -- are called allergens. If you're predisposed to allergies and come in contact with an allergen for the first time, your body will produce antibodies called immunoglobulin E or IgE. These IgE antibodies attach themselves to certain cells (called mast cells) in the eyes, nose, lungs and gastrointestinal tract. There, they wait for contact with the specific allergen again.
When that contact happens, the IgE antibodies capture the allergen. This causes the release of chemicals such as histamine and leukotriene. In turn, these chemicals cause symptoms such as runny nose, itching, sneezing, wheezing and coughing.

There are many types of IgE antibodies, and each type looks for only one specific allergen. Your body may produce the IgE antibody that recognizes only pollen. Or, you may have multiple types of IgE antibodies and be allergic to multiple allergens, such as pollen, mold and animal dander.


Causes/associated factors
Although anyone can develop allergies at any age -- even to substances you've been exposed to throughout your life -- most experts agree that heredity plays a role. If one or both of your biological parents had allergies, for example, you have a greater risk of developing them yourself. Your allergies may be different than those of your parents, however.
Allergies can develop from many different things, such as:

ragweed, grass or tree pollens
dust
mold
insect venom (from fire ants, bees, wasps or yellow jackets, for example)
cockroaches
pets (such as cats, dogs, hamsters or gerbils)
food (such as peanuts, tree nuts, fish, shellfish, eggs, milk, soy or wheat)
latex (rubber)
medications (such as penicillin, sulfa, asprin or X-ray dye)
Types of allergic reactions include:

contact dermatitis, some forms of atopic dermatitis or eczema, a rash that appears after an allergen exposure
allergic rhinitis (hay fever), a cold-like reaction to an allergen that contacts the lining of the nose and eyes
asthma, a breathing disorder that may be triggered by specific allergens
hives, a rash that's often related to certain medications, foods or infections
anaphylaxis, a severe life-threatening reaction that can be triggered by factors such as certain medications or foods, exposure to latex or insect stings
Allergies can be seasonal (confined to a specific season) or perennial (occur throughout the year). Seasonal allergies, such as hay fever and grass or pollen allergies, occur when the allergen is at a high level in the environment. Of course, these levels can vary significantly from one geographic area to another. Perennial allergies are reactions to indoor allergens such as fungi, cockroaches, dust mites and animal dander.


Signs/symptoms
Allergy symptoms depend on the specific allergen, its concentration and how long you were exposed. Symptoms vary and may include:
red, itchy eyes
itchy nose, throat, ears and, possibly, roof of the mouth
stuffy or congested nose, causing you to breathe through your mouth
watery, clear nasal drainage
postnasal drip that may produce a cough or sore throat
loss of smell and taste
decreased ability to hear
bad breath
itchy skin or hives
chronic, inflamed skin rashes
wheezing
Severe, life-threatening allergic responses are a medical emergency. The first symptom may be a feeling of impending doom. Other symptoms may include:

generalized hives (a sudden bumpy or welt-like, itchy rash)
difficulty breathing
wheezing
swelling of the throat, tongue, lips or eyes
difficulty swallowing
nausea, vomiting, diarrhea or abdominal cramps
chest tightness
seizures
shock
Anaphylaxis is life-threatening. Call 911 immediately for medical assistance! If you have a life-threatening allergic condition, wear a medical identification tag that lists your allergies and any other serious medical conditions. Your doctor may also recommend carrying an emergency epinephrine injection pen (sometimes called an EpiPen) at all times. If you have a serious allergic reaction, an emergency epinephrine shot may save your life by temporarily halting the severe response and giving you time to seek medical attention.


Diagnosis
The doctor will review your medical history and do a physical exam. In some cases, skin testing -- which involves placing a small amount of a specific allergen under your skin -- is needed to pinpoint exactly what you're allergic to. Redness and swelling at the site indicates an allergy to the particular substance. Skin testing can't be done under some circumstances, however, such as when you're taking a medication that may interfere with the results or if you have certain skin conditions.
In these cases, blood tests can be done instead. For example, with a radioallergosorbent test (RAST), a blood sample is combined with particles of specific allergens to determine your response. RAST isn't done routinely because it's more costly than skin testing and may not be as accurate.

Your doctor may recommend keeping a daily diary of symptoms to help determine the source of your allergy.


Treatment
Above all, avoid exposure to the allergen. (See below for specific tips.) If you can't completely avoid the allergen, minimize your exposure as much as possible. Sometimes, you may need to use medication or take other steps to ease your symptoms. Depending on the circumstances, your doctor may refer you to an allergist (a doctor who specializes in the treatment of allergies).
Medications
It's best to discuss the use of allergy medications, both over-the-counter and prescription products, with your doctor. Some are better suited for specific allergies than others. Some may not be appropriate if you have certain medical conditions, such as heart disease, high blood pressure or diabetes. Also discuss potential side effects.

Your doctor may recommend one or more of the following:

Antihistamines: Antihistamines often cause drowsiness. Recently, however, the U.S. Food and Drug Administration (FDA) approved nonsedating antihistamines for over-the-counter use. People who become drowsy after taking antihistamines now have other over-the-counter options. Common antihistamines include diphenhydramine (Benadryl, for example), chlorpheniramine, clemastine, cetirizine (Zyrtec, for example), loratadine (Claritin or Alavert, for example) and fexofenadine (Allegra, for example).
Benefits: Antihistamines help block the histamine effect, such as runny nose, sneezing, and itchy eyes and nose.

Risks: Antihistamines don't help much with congestion.


Decongestants: Decongestants can be taken orally, as nasal sprays or as eyedrops. Pseudoephedrine (Sudafed, for example) is a common oral decongestant. Common nasal sprays include phenylephrine (Neo-Synephrine, for example) and oxymetazoline (Afrin, for example). Nasal sprays should only be used for up to a few days. When used longer, they can actually increase nasal congestion and cause dependency.
Benefits: Decongestants help narrow the blood vessels in the nose, leading to less mucus production and therefore less congestion.

Risks: Decongestants can increase heart rate, and cause anxiety and difficulty sleeping.


Cromolyn products: Cromolyn products work in various ways to minimize allergy symptoms. Available by prescription in inhalant or tablet form, these products work best when taken before allergy symptoms develop. Often, they must be taken three to four times a day. Cromolyn sodium spray (Nasalcrom, for example) is also available over the counter as a nasal spray for people older than age 2.
Benefits: Cromolyn products help prevent mast cells from releasing histamine, reducing symptoms such as runny nose, sneezing, and itchy eyes and nose.

Risks: Cromolyn products have few side effects, but can cause cough due to irritation.


Leukotriene modifiers: Leukotriene modifiers are used more commonly for people who have asthma. Montelukast (Singulair, for example) is one of the newer antileukotriene medications used to prevent asthma and allergy symptoms.
Benefits: Leukotriene modifiers help block the effect of leukotriene. They help with early responses to allergens, such as itching and sneezing, as well as the later responses, such as congestion.

Risks: A few side effects are possible.


Corticosteroids: Corticosteroid medications are most effective with regular use. They can be injected, inhaled, taken by mouth, or taken as a nasal spray, cream, ointment or eyedrop. With the exception of milder skin creams, corticosteroids are available by prescription only.
Benefits: Corticosteroids are often very effective but reserved for more severe symptoms or when antihistamines aren't effective.

Risks: Side effects depend on which form you take and for how long. Again, discuss potential side effects with your doctor.


Nasal saline sprays: Nasal saline sprays relieve dry, inflamed membranes in the nose. These products are often available without a prescription.
Immunotherapy (allergy shots)
If avoidance and medication don't adequately control your symptoms, your doctor may recommend immunotherapy, or allergy shots. With these shots, small amounts of a known allergen are injected into your system. To help you build immunity, the amount of allergen increases with each shot. A full course of immunotherapy often requires regular injections over three to five years or even longer.

Immunotherapy has been shown to be helpful for people with allergic rhinitis, allergic conjunctivitis, allergic asthma and hypersensitivity to stinging insects. Clinical trials have not supported immunotherapy for people who are sensitive to certain foods.

Benefits: Immunotherapy may provide continued improvement for years after therapy ends.

Risks: Reactions at the injection site or throughout the body are possible. Rarely, anaphylaxis may occur.

Although immunotherapy isn't a cure for allergies and improvement isn't guaranteed, it may decrease your sensitivity to a specific allergen. If you're severely allergic to bee stings, for example, allergy shots can reduce the threat of a severe reaction, as well as relieve the probable anxiety associated with being outdoors.


Complications
People who have allergic rhinitis may develop secondary bacterial infections such as sinusitis (an infection of the nasal sinuses) or otitis media (an infection of the middle ear).

Pregnancy-specific information
Pregnancy does not increase the risk of developing allergies. If your allergies flare up during pregnancy, your doctor may recommend different treatments than those described above.

Senior-specific information
Growing older is not a risk factor for developing allergies. In fact, some allergies may improve as you age.

Prevention
If you have allergies, ask your doctor for suggestions on specific ways to avoid the allergens that affect you. Here are some general recommendations:
Pollens

Keep windows and doors closed (including vehicle windows). Avoid window and attic fans that draw in air from outside. Use air conditioning.

Pay attention to high pollen counts, and avoid being outside if possible. Different pollens have different peak pollen times. For example, ragweed peaks in the late morning and grasses in the afternoon.

After being outdoors, take a bath or shower and change your clothes. Don't hang clothes outside to dry.
Outdoor molds and fungi

Don't walk through uncut fields, rake leaves, or work with compost or dry soil.

Keep windows and doors closed (including vehicle windows). Avoid window and attic fans that draw in air from outside. Use air conditioning.
Indoor molds and fungi

Try to reduce indoor humidity to less than 50 percent by using an air conditioner and dehumidifier.

Clean moldy surfaces, and fix all water leaks in the house.

Use exhaust fans in the bathroom and kitchen to remove moisture. Vent the clothes dryer outside.
House dust mites

Cover your mattress, box springs and pillow with microporous or polyurethane-coated covers. Wash bedding in hot water (130°F) every week.

Try to reduce indoor humidity to less than 50 percent by using an air conditioner and dehumidifier.

Minimize dust by limiting upholstered furniture, carpets or rugs on the floor and other dust-collecting items, such as stuffed toys.

Consider a high-efficiency particulate absorption (HEPA) filter to remove allergens from the air.
Animals

Keep your pet out of the bedroom, and keep the bedroom door closed.

Keep your pet off upholstered furniture and, if possible, the carpet and rugs.
Food

Read product labels carefully, and ask about ingredients when someone else prepares your food. Many foods contain ingredients that may not be readily apparent.
Medication

Remind all members of your health care team about your allergies, including your pharmacist.