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An allergic reaction is a response of the immune system to a trigger, known as an allergen. The immune system is designed to fight harmful substances. But sometimes the system can overreact causing allergy symptoms. A serious allergic reaction is known as anaphylaxis.
Medicines are a common cause of allergic reactions. Allergic reactions may also result from pollen, food, pets, insect stings, and other causes. Depending on the body’s response, an allergic reaction may be mild or severe. In most cases, allergic reactions are mild and can be treated with over-the-counter medications.
Severe allergic reactions can be life-threatening and need immediate medical treatment. Families should know the symptoms of an allergic reaction and have an action plan for emergencies. It is important to avoid what caused the allergic reaction to prevent another reaction in the future.
|Mild Allergic Reaction||Severe Allergic Reaction|
|Runny or stuffy nose||Swelling of mouth, tongue, lips, throat, or eyes|
|Sneezing||Low blood pressure|
|Itching||Dizziness or fainting|
|Watery eyes||Trouble swallowing or breathing|
|Skin redness or rash||Nausea or vomiting|
Any type of medicine can cause a reaction. However, some medicines have a higher risk of drug allergy. These include:
The most common symptoms of a drug allergy are rash, hives, itching, wheezing, or swelling. A more severe allergic reaction may occur, called anaphylaxis. Symptoms of anaphylaxis include facial swelling, throat swelling, trouble swallowing, trouble breathing, nausea or vomiting, low blood pressure, and dizziness or fainting.
Anaphylaxis can sometimes cause the body to go into shock. This results in a lack of blood flow, and cells cannot get the oxygen they need. Anaphylactic shock can be fatal if the person does not receive immediate medical treatment.
Most allergic reactions occur within hours of taking the drug. But in more rare cases, allergic reactions can occur later. Sometimes it can be hard to identify the cause of a reaction. The care team may look at factors such as the timing of the reaction, whether the drug is known to cause a reaction, what happened when the drug was stopped or taken again, and whether there are other possible reasons for the symptoms.
A person may be at higher risk for a drug allergy based on certain factors such as:
Yes, it is possible for an allergic reaction to develop at any time. The timing of when an allergic reaction occurs is different for each person. Some may experience a reaction after the first dose of a drug. Other people may experience a reaction after taking the drug multiple times.
In addition, the first time you a take a drug, you may have no allergic reaction. This is because your body is processing the drug and preparing its response. Your body identifies the drug as a harmful invader and develops a substance called an antibody. Later, when you take the drug again, the antibody senses the drug and tells your body to fight which leads to the allergic reaction symptoms.
Yes, drug allergies can change over time. For example, many people who are allergic to penicillin eventually outgrow this drug allergy. A doctor or pharmacist can answer questions about drug allergy status and whether this might change. A patient with a previous history of drug allergy should be evaluated by an allergist or immunologist before using the medicine again.
Pharmacists are trained to educate patients about drug allergies.
It is essential to prepare and have an action plan in place to manage a severe allergic reaction. A severe allergic reaction needs urgent medical care as soon as possible. Do not wait to see if an allergic reaction improves or worsens. Call 911 immediately. A severe allergic reaction can lead to death.
After a severe allergic reaction, symptoms can return. Patients may need medical care and monitoring for a period of time to make sure that the reaction has fully resolved.
The following guide can help during and after an allergic emergency:
S — Seek immediate medical help.
A — Identify the allergen. What may have caused the reaction?
F — Follow up with a specialist. An allergist or immunologist is a doctor who specializes in allergies.
E — Carry epinephrine for emergencies.
Reviewed: December 2019