What is an allergic reaction?
Your immune system is responsible for defending the body
against bacteria and viruses. In some cases, your immune system will defend
against substances that typically don’t pose a threat to the human body. These
substances are known as allergens, and when your body reacts to them, it causes
an allergic reaction. You can inhale, eat, and touch allergens that cause
a reaction. Doctors can also use allergens to diagnose allergies, and can
even inject them into your body as a form of treatment.
Academy of Allergy, Asthma & Immunology (AAAAI) reports that as many as
50 million people in the United States suffer from some type of allergic
What causes an allergic reaction?
Doctors don’t know why some people experience allergies.
Allergies appear to run in families and can be inherited. If you have a close
family member who has allergies, you’re at greater risk for developing
Although the reasons why allergies develop aren’t known,
there are some substances that commonly cause an allergic reaction. People who
have allergies are typically allergic to one or more of the following:
- pet dander
- bee stings or bites from other insects
- certain foods, including nuts or shellfish
- certain medications, such as penicillin or
- certain plants
- pollen or molds
What are the symptoms of an allergic reaction?
The symptoms of an allergic reaction can vary from mild to
severe. If you become exposed to an allergen for the first time, your symptoms
may be mild. These symptoms may get worse if you repeatedly come into contact
with the allergen.
Symptoms of a mild allergic reaction can include:
- hives (itchy red spots on the skin)
- nasal congestion (known as rhinitis)
- scratchy throat
- watery or itchy eyes
Severe allergic reactions can cause the following symptoms:
cramping or pain
or tightness in the chest
of the face
of the face, eyes, or tongue
A severe and sudden allergic reaction can develop within
seconds after exposure to an allergen. This type of reaction is known as
anaphylaxis and results in life-threatening symptoms, including swelling of the
airway, inability to breathe, and a sudden and severe drop in blood pressure.
If you experience this type of allergic reaction, seek immediate emergency
help. Without treatment, this condition can result in death within 15 minutes.
How is an allergic reaction diagnosed?
Your doctor can diagnose allergic reactions. If you
experience symptoms of an allergic reaction, your doctor will perform an exam
and ask you about your health history. If your allergic reactions are severe,
your doctor may ask you to keep a journal that details your symptoms and the substances
that appear to cause them. Your doctor may want to order tests to determine
what’s causing your allergy. The most commonly ordered types of allergy tests
A skin test involves
applying a small amount of a suspected allergen to the skin and watching for a
reaction. The substance may be taped to the skin (patch test), applied via a
small prick to the skin (prick test), or injected just under the skin
(intradermal test). A skin test is most valuable for diagnosing:
pollen, and animal dander allergy
allergy (such as mosquito bites or bee stings)
contact dermatitis (a rash you get from touching a substance)
Challenge testing is
useful in diagnosing food allergies. It involves removing a food from your diet
for several weeks and watching for symptoms when you eat the food again.
A blood test for
an allergy checks your blood for antibodies against a possible allergen. An
antibody is a protein your body produces to fight harmful substances. Blood
tests are an option when skin testing isn’t helpful or possible.
How is an allergic reaction treated?
If you experience an allergic reaction and you don’t know
what’s causing it, you may need to see your doctor to determine what the cause
of your allergy. If you have a known allergy and experience symptoms, you may
not need to seek medical care if your symptoms are mild. In most cases,
over-the-counter antihistamines, such as diphenhydramine (Benadryl), can be
effective for controlling mild allergic reactions.
If you or someone you know experiences a severe allergic
reaction, you should seek emergency medical attention. Check to see if the
person is breathing, call 911, and provide CPR if needed. People with known
allergies often have emergency medications with them such as an epinephrine
auto-injector (EpiPen). Epinephrine is a “rescue drug” because it opens the
airways and raises blood pressure. The person may need your help to administer
the medication. If the person is unconscious, you should:
the person flat on their back.
the person’s legs.
the person with a blanket.
This will help prevent shock.
What is the long-term outlook?
If you have a known allergy, preventing an allergic reaction
will improve your outlook. You can prevent these reactions by avoiding the
allergens that affect you. If you have serious allergic reactions, you should
always carry an epinephrine auto-injector and inject yourself if symptoms
Your outlook will also depend on the severity of your
allergy. If you have a mild allergic reaction and seek treatment, you will have
a good chance for recovery. However, symptoms may recur if you come into
contact with the allergen again. If you have a severe allergic reaction, your
prognosis will depend on receiving quick emergency care. Anaphylaxis can result
in death. Prompt medical care is necessary to improve your outcome.
How can you prevent an allergic reaction?
Once you identify your allergy, you can:
exposure to the allergen.
medical care if you are exposed to the allergen.
medications to treat anaphylaxis.
You may not be able to avoid an allergic reaction completely,
but these steps can help you to prevent future allergic reactions.