The majority of allergy treatments are designed to ease symptoms of an allergic reaction that has already occurred. There are some treatments, however, designed to prevent allergic reactions in people with known allergies. The goal of such treatments is one or more of the following:

• Prevent the onset of symptoms
• Lessen the frequency of reactions
• Lessen the severity of symptoms resulting from a reaction

The only treatment that can completely prevent an allergic reaction from occurring is the total avoidance of any known allergens (e.g., pollen, dust, pet dander). However, avoiding an allergen is often difficult when the allergen is constantly present or an individual is highly sensitive.

One resource that is very useful to people trying to avoid the airborne allergens common to allergic rhinitis (hay fever) is the pollen and mold report. This report describes the current amount of airborne allergens present in grains per cubic meter of air. Individuals who are sensitive to airborne allergens can use the report to determine when they should remain indoors. The report is divided into four separate counts: tree pollen, grass pollen, weed pollen and mold spores. 

The allergy index is another useful tool. It is a measure of the number of people affected by pollen in a certain region. Based on a scale of 1 to 10, it takes into account both the amount of pollen present in the air and how sensitive most people are to the pollen types present.

Individuals with food allergies should learn to always check food ingredient labels for problematic foods. Oftentimes what seems like a harmless food will actually contain unexpected substances. For example, some types of beer and wine contain egg proteins, which can be dangerous to people with an egg allergy. People with food allergies must also learn what other names their problem food might be listed as. For example, individuals with an egg allergy must avoid extracts such as albumin, globulin and livetin with equal care.

Allergy shots are the only treatment currently available for preventing allergy symptoms over a long period of time. By using this method, also known as immunotherapy, an individual can become gradually desensitized to a specific allergen. 

While many medications are used to treat the symptoms of allergies, some medications can be taken prior to contact with an allergen to prevent or reduce symptoms. These include:

• Leukotriene modifiers. Can be taken preventatively to reduce or completely prevent some allergy symptoms. These medications disrupt the function of leukotrienes (involved with the constriction of airways in the lungs). The immune system produces leukotrienes during an allergic reaction.
  
  
• Antihistamines. Can lessen the severity of an allergic reaction by disrupting the allergic cascade. When antihistamines are present in the bloodstream during an allergic reaction, histamines are released, but are blocked from carrying out their normal functions. This means that the symptoms usually caused by histamines, such as itchiness and runny nose, are lessened or prevented. Because they can effectively prevent allergy symptoms, some people take antihistamines on a daily basis.
  
  
• Corticosteroids. Can be taken preventively to reduce or prevent allergy symptoms by counteracting swelling, inflammation and mucus secretions. For the best results, corticosteroids should be taken every day with regularity, and the drug must remain in the body for at least a week to be effective.

The use of air filters can be very effective at reducing the number of airborne allergens in an enclosed space. High-efficiency particulate air (HEPA) filters are one of the most highly effective kinds of filter currently available. By forcing air through screens with microscopic pores, HEPA filters are capable of filtering out at least 90 percent of all particles larger than 0.3 microns, which prevents their release back into the air. HEPA filters can help to substantially diminish the amount of pollen, airborne mold and dander found in a room.