There are many allergies from which people suffer. They all have essentially the same root, however, which is your body's immune system reacting to some form of substance it detects as dangerous. To fight this, it produces substances, including histamines. These cause the symptoms common to allergies such as itching, sinus congestion, rash and others, including in severe cases, anaphylaxis, which can be life threatening.
Food
If you are allergic to any type of food, from eggs to nuts to dairy products, your body's immune system detects these on ingestion and releases chemicals to fight them. Food allergies are more common in children than adults. The Mayo Clinic reports 6 percent to 8 percent of children who are age 3 or younger have food allergies. Approximately 4 percent of adults have them. Children frequently outgrow their allergic reactions to food. Food allergy symptoms can include fainting, a tingling sensation in your mouth, lightheadedness, hives, facial swelling and breathing difficulties. As with all allergies, food allergies also can cause a severe reaction termed anaphylaxis. Some of the symptoms of this are similar to those listed above but also include tightening and construction of your airways, throat swelling that also can make it hard to breathe, a blood pressure drop that is severe as part of shock, an increase in the pulse rate and unconsciousness.
Drugs
Both over-the-counter and prescription-level drugs can cause allergic reactions in some people. Two of the most common are aspirin and penicillin allergies. Again, the most serious of the symptoms of an allergy to a drug is anaphylaxis and emergency treatment is required for any such reaction. Other symptoms may include a rash on the skin or hives, a fever, dizziness, shortness of breath and swelling of the face.
Airborne Allergens and Insects
Allergic rhinitis, commonly known as hay fever, can be caused by anything from pet dander to dust mites to pollen that is airborne. It can be a chronic condition or occur only during a specific season, particularly spring, summer and fall. The reactions in people can vary tremendously, from minor irritation to incapacitation. This type of allergy may produce such symptoms as those similar to a cold--cough, sneezing, a runny nose, nasal congestion and watery eyes--but they do not go away when the typical duration of a cold would end. Other symptoms include itching on the nose, throat or upper part of the mouth, facial pain, pressure in the sinuses and decreases in your ability to taste or smell. Others include irritability, fatigue and insomnia. The bites or stings from insects such as bees also can cause allergic reactions, including anaphylaxis.
