Allergy Treatment

Once you develop allergies, you cannot prevent them. What you can do is avoid the allergens that cause them.
You should consult with your doctor on the efficacy of getting allergy shots, which are meant to desensitize you to allergens so that you no longer have allergic reactions. There is still some debate over whether such injections work for everyone.
Antihistamines may help suppress symptoms, though most will cause drowsiness. A few such as Claritin seem not to cause this side effect.
Other drugs that can alleviate symptoms are decongestants, nasal sprays and corticosteroids.
If sensitive to outdoor allergens such as pollen, stay indoors during the heaviest concentrations of it or when it's windy. Turn on your air conditioner (making sure that the filters are clean) both in your house and car. Clean your dog or cat after it's been outside as pollen can cling to fur; or give your pet away. Take a shower yourself after being outdoors.
Consider purchasing an air purifier for rooms that you spend the most time in.
If allergic to dust, keep your house clean. Get rid of carpets and other fabrics, such as curtains. Wash clothes and bedding often. Do not use down pillows or comforters.
If you consistently suffer from allergies, regardless of whether it's pollen season or not, it may be that you are allergic to a particular food or food additive. UC Berkeley's The New Wellness Encyclopedia recommends the following for people with mild to moderate allergies: Take your resting pulse (in a 60-second count), then try a little of the food (in as pure a form as possible) you suspect may be causing your allergies. Take your heart rate 15-20 minutes after consumption. If your heart rate is more than 10 beats faster per minute, you're allergic to that food. Eliminate it from your diet. Do not pursue this recommendation if your allergies are severe as anaphylactic shock can result.