An allergy develops when your body's immune system initiates an abnormal response to a specific substance, or allergen, such as animal dander, milk products or insect stings. The allergy side effects you experience when exposed to an allergen can vary depending upon the type and severity of your allergy.
Nasal Congestion
Allergens in the air can enter your body through your nasal passages, causing irritation within your nose. If this occurs, your body may begin to produce excess mucus within your nose to prevent the allergen from entering your lungs. This can cause you to develop a stuffy or runny nose. Sneezing can also occur as an allergy side effect, causing you to frequently need to blow your nose.
Skin Irritation
Coming into contact with allergy-inducing substances, such as pets or certain food products, can cause skin irritation to develop in allergic individuals, explains Medline Plus, a medical website provided as a service of the National Institutes of Health. If an allergen manages to get into your blood stream, such as through an insect sting, you can develop hives or welts across your entire body. These skin-related allergy side effects can cause your skin to appear red, irritated or inflamed. Your skin may also become dry, flaky or itchy.
Breathing Difficulties
If you breathe in an airborne allergen, you can develop lung-related side effects due to allergy. Allergens within the lungs can cause irritation and inflammation, which may lead to narrowing of your airway passages. When this happens, it becomes more difficult for oxygen to reach your lungs, which can cause you to experience shortness of breath or breathing difficulties. Allergy patients can also begin to wheeze or cough as a side effect of allergen exposure.
Eye Irritation
Airborne allergens can come in contact with and irritate the sensitive lining of your eyes. If this occurs, you can develop itchy, watery eyes that appear red or bloodshot. Be sure to wash your hands after handling allergen-containing items to prevent spreading these allergens to your eyes or facial skin.
Oral Swelling
If you ingest an allergen, you can develop oral allergy side effects. Such side effects can cause a tingling sensation to occur within your mouth or throat, which may cause itching. Certain people also experience swelling of the lips, tongue or throat after consuming an allergen. These allergy side effects can be severe and may interfere with your ability to breathe normally. Emergency medical help might be required.
Upset Stomach
After eating a food that contains an allergen, you can experience an upset stomach as an allergy side effect, explains the Better Health Channel, a health information website provided by the Australian government. A food allergy can cause nausea, vomiting, stomach cramping or diarrhea to develop shortly after consuming an allergen.
Anaphylaxis
Certain allergens can cause severe, life-threatening allergy side effects to develop in some patients---a condition called anaphylaxis. Side effects of anaphylaxis require immediate emergency medical attention and can include dizziness, decreased heart rate, rash, oral swelling, stomach upset, breathing difficulties and loss of consciousness.
