An allergy describes the body's reaction after being exposed to a substance to which it is allergic.
What triggers allergies?
The substance that triggers the allergic reaction is called an allergen. An allergen may be harmless to most people, but lead to severe allergic reactions in others.
There are many different allergens, but the most common are pollens (such as grass or trees), dust mites, mold spores, foods (egg, milk, nuts, seafood), pet dander (cats, dogs or birds) insect stings, latex, and medications.
A person can be allergic to many different allergies.
Some allergy symptoms occur year round (perennial allergies). These include those triggered by indoor allergens, such as dust mites and mold. Others allergies occur only at certain times of year (seasonal allergies). These are usually due to allergens that come and go with the season, such as pollens.
What are the symptoms of allergies?
Allergy symptoms vary depending on the part of the body that is affected, but allergies almost always involves itching.
When the eyes react to allergens, it is called allergic conjunctivitis ("eye allergies"). The eyes may start to itch, turn red and produce excessive tears.
When the nasal passages (nose and sinuses) react to allergens, it is called allergic rhinitis. The symptoms include itching, nasal congestion and increased mucus production (runny nose).
Allergy symptoms may also arise on the skin in the form of itching, red patches called hives (urticaria).
Allergies can also trigger an asthma attack in those with underlying asthma. This is called allergic asthma and results in coughing, wheezing and difficulty breathing.
What causes allergies?
There are different types of allergic reactions, but the allergies that most people suffer, are due to a type of allergic response called a type 1, or “immediate hypersensitivity”. The symptoms develop immediately after exposure to the allergen. During a type 1 allergic reaction, cells in the immune system release a chemical signal called histamine that rapidly leads to swelling and itching. The immune cells also create a specific type of immunoglobulin called IgE that is designed to rid the body of the allergen. (see allergy tests).
Other types of allergies, such as allergic contact dermatitis, involve a different type of immune reaction called type 4 or “delayed-type hypersensitivity”. Symptoms of this type of allergic reaction take longer to develop. For instance, the rash that develops following contact with poison oak or ivy can take 2-3 days to develop.
How are allergies diagnosed?
Itching, and the rapid onset of symptoms are suggestive of a possible allergy. If necessary, allergy tests can be performed to distinguish allergies from other medical conditions.
Depending on the severity and duration of symptoms, it may be helpful to identify the specific allergen to which someone is allergic. This can be performed through skin allergy tests or blood tests (RAST).
How are allergies treated?
Allergies are best treated by eliminating exposure to the allergen. This might include measures to create an allergen-free home that reduces exposure to dust mites, mold or pet dander.
However, this may not be feasible for those with pollen, mold, and other allergens.
There are fortunately a variety of allergy medications available that can provide safe and effective control of allergy symptoms for many people.
Categories of allergy medications include the following:
- Antihistamine, oral. Antihistamines block the “histamine’ that leads to swelling and itch. Antihistamines are most effective when started before peak allergy season or at the earliest signs of allergy symptoms. Commonly used antihistamines, such as diphenhydramine (Benadryl) or chlorpheneramine are notorious for causing drowsiness. A group of nonsedating antihistamines (fexofenadine, loratadine and others) are available but they are more expensive.
- Anthistamine, nasal spray. These may be recommended to control symptoms of allergic rhinitis and to avoid exessive use of oral antihistamines.
- Antihistamine, ophthalmic. These eye drops are used to control symptoms of allergic conjunctivitis.
- Corticosteroid, nasal sprays. These are an effective alternative to antihistamines for those with specific symptoms of allergic rhinitis (hay fever).
- Corticosteroid, ophthalmic. These eye drops may be used for symptoms of allergic conjunctivitis.
- Cromolyn, nasal spray (Nasalcrom®). This over-the-counter medication for nasal allergies must be used before exposure to an allergen.
- Decongestants, nasal (oxymetazoline). Nasal sprays are intended for short-term relief only. They can result in increased nasal congestion if used for more than three days without a break.
- Decongestants, oral (phenylephrine and pseudoephedrine). Decongestants may be used for immediate relief of nasal congestion that occurs with allergic rhinitis. Side effects from oral decongestants can include insomnia, high blood pressure, and a racing heart rate. Consult your health-care provider before using these medications if you have high blood pressure, a history of stroke, or heart disease.
Your doctor or health care provider will prescribe or recommend one or more allergy medications depending on several variable, including the severity and duration of symptoms, response to past treatments, and the presence of other medical conditions.
Immunotherapy may be considered for those who do not get sufficient relief of their allergy symptoms from safe doses of allergy medications.
Immunotherapy (Allergy shots)
Allergen immunotherapy, or "allergy shots”, may be recommended to decrease a person’s sensitivity to specific allergens. Allergy shots involve injecting increasing amounts of an allergen to a patient over several months or years. Each shot contains a tiny amount of the allergen, just enough to stimulate the body’ immune system, but not enough to cause a full-blown allergic reaction.
The allergy shots must be developed for each person depending on the substances to which he or she is allergic. Allergy shots are usually reserved for people with allergy symptoms that significantly impact their lives, cannot avoid the allergen, and are not sufficiently controlled with allergy medications.
Risk of Anaphylaxis
Some people with allergies are at risk of developing a severe, life-threatening allergic reaction, called anaphylaxis.
People with latex allergies, bee sting allergy, food allergies (peanuts, shellfish), or medication allergies (penicillin) are more likely to develop severe allergic reactions after exposure to the allergen. However, anaphylaxis can develop in response to nearly any allergy.
People at risk of developing anaphylaxis may be advised to have access to injectable epinephrine, such as Epipen® or Twinject® auto-injectors, and to wear a medical bracelet with information about their allergies.