What is an allergic reaction? Causes, symptoms, diagnosis and treatment

Posted by Master, Doctor Mai Vien Phuong - Department of Examination & Internal Medicine - Vinmec Central Park International General Hospital

It is not clear why some people develop allergies. However, the condition is often familial and inherited. If you have a family member with allergies, you are more likely to develop an allergy.

The immune system is responsible for protecting the body against bacteria and viruses that cause disease. However, in some cases the immune system will fight off substances that are not dangerous to humans. These substances are called allergens, and when the body reacts to them, it causes symptoms of an allergic reaction.
The patient can inhale, ingest, and touch the allergens that cause reactions. As a result, your doctor will likely use allergens to diagnose allergies and even inject them into your body as a treatment.
2. What causes an allergic reaction? It's not clear why some people develop allergies. However, the condition is often familial and inherited. If you have a family member with allergies, you are more likely to develop an allergy.
Although the reason why allergies are not known, there are certain substances that commonly cause allergic reactions. People with allergies are usually allergic to one or more of the following substances:
Pet dander Bee stings or other insect bites Certain foods, including nuts or shellfish Some medications, such as penicillin or aspirin Certain plants Pollen or mold

3. What are the symptoms of an allergic reaction? Symptoms of an allergic reaction can vary from mild to severe. In the event that you are exposed to an allergen for the first time, the symptoms may be mild. But with repeated exposure, it can get worse.
Symptoms of a mild allergic reaction include:
Rash (itchy red bumps on the skin) Itching Nasal congestion (known as rhinitis) Itchy throat Watery eyes or itchy eyes Serious allergic reaction including These include:
Abdominal cramps or pain Chest pain or tightness Diarrhea Difficulty swallowing Dizziness Fear or anxiety Flushing face Nausea or vomiting Fast heartbeat Swelling of face, eyes or tongue Fatigue Wheezing Shortness of breath Fainting Severe and sudden allergic reactions can appear within seconds of exposure to an allergen. This reaction is called anaphylaxis and leads to life-threatening symptoms, including swelling of the airways, difficulty breathing, and a sudden drop in blood pressure.
If this type of allergic reaction is experienced, seek emergency medical help. If not treated in time, this condition can lead to death for the patient.
4. How are allergic reactions diagnosed? If you experience symptoms of an allergic reaction, your doctor will examine you and ask about your medical history. If you have a severe allergic reaction, your doctor may ask you to keep a detailed record of your symptoms and triggers.
Also your doctor will order tests to determine the cause of the condition including:
Skin prick test Checking your body for antigens Blood test Skin prick test done by applying Apply a small amount of the suspected allergen to the skin and then monitor for a reaction. This substance can be applied to the skin (patch test) or applied through a small prick in the skin or injected just under the skin.
The most valuable skin test for diagnosing an allergy is:
Food allergy Mold, pollen and animal dander allergy Penicillin allergy Venom allergy Allergic contact dermatitis Blood test aimed at target for antibodies against the allergen. Antibodies are a type of protein that the body produces to fight harmful substances. Blood testing is done when skin testing is not diagnostic or cannot be performed.

5. How are allergic reactions treated? If you're having an allergic reaction and don't know what's causing it, you may need to see your doctor to determine what's causing your allergy. If you have a known allergy and have symptoms, you may not need to see a doctor if your symptoms are mild.
In most cases, over-the-counter antihistamines are used to control mild allergic reactions. However, if you have a severe allergic reaction, urgent medical attention should be sought.
People with known allergies often carry emergency medication, such as an epinephrine auto-injector (EpiPen).
6. How can an allergic reaction be prevented? If you already have an allergy, preventing an allergic reaction will improve your outlook. You can prevent these reactions by avoiding your allergen. If you have severe allergic reactions, you should always carry an EpiPen and inject yourself if symptoms occur.
Once you have determined your allergy, you should:
Avoid contact with the allergen. Seek medical attention if you come into contact with an allergen. Bring medication to handle anaphylaxis. You may not be able to avoid an allergic reaction completely, but these steps can help you prevent future allergic reactions.

References:
Allergy overview. (2016). my.clevelandclinic.org/health/articles/overview-of-allergies Allergic reactions. (n.d.). aaaai.org/conditions-and-treatments/library/at-a-glance/allergic-reactions.aspx Delves PJ. (n.d.). Overview of allergic reactions. merckmanuals.com/home/immune-disorders/allergic-reactions-and-other-sensitive-disorders/overview-of-allergic-reactions Mayo Clinic Staff. (2014). Allergy skin tests: What you can expect. mayoclinic.org/tests-procedures/allergy-tests/basics/what-you-can-expect/prc-20014505