Allergy
An allergy is a medical condition in which the immune system reacts abnormally to a substance that is usually harmless to most people. These substances are called allergens. When a person with an allergy comes into contact with an allergen, the immune system may produce antibodies and release chemicals such as histamine, leading to symptoms that can affect the skin, nose, eyes, respiratory system, digestive system, or the entire body. Allergies can occur at any age and may be seasonal or present throughout the year. Some allergies cause mild symptoms, while others can cause a severe and potentially life-threatening reaction called anaphylaxis. Common allergens include foods, medicines, insect venom, pollen, mold, dust mites, and animal dander.
Allergy symptoms vary depending on the allergen, the route of exposure, and the severity of the reaction. Common symptoms include:
- Sneezing
- Runny or stuffy nose
- Itchy nose or throat
- Itchy, watery, red, or swollen eyes
- Itchy skin
- Skin rash
- Hives
- Facial swelling
- Swelling at the site of an insect sting
- Swelling of the lips, tongue, face, or throat
- Tingling or itching in the mouth
- Cough
- Wheezing
- Chest tightness
- Shortness of breath
- Difficulty breathing
- Nausea, vomiting, abdominal pain, or diarrhea in some allergic reactions
Anaphylaxis is a severe allergic reaction that can develop rapidly and requires immediate medical attention. It may cause:
- Difficulty breathing or severe shortness of breath
- Wheezing
- Swelling of the tongue or throat
- Tightness in the throat
- Difficulty swallowing or speaking
- Dizziness, fainting, or confusion
- A rapid or weak pulse
- Widespread hives or flushing
- A sudden drop in blood pressure
- Loss of consciousness
Anaphylaxis is a medical emergency. If a person has a prescribed epinephrine (adrenaline) auto-injector, it should be used immediately as directed, and emergency medical care should be sought. A person experiencing a severe allergic reaction should not be left alone.
Allergies occur when the immune system mistakenly identifies a normally harmless substance as a threat. The immune response can then trigger the release of chemicals that produce allergy symptoms.
1. Animal products
Animal dander, saliva, urine, and other animal proteins can trigger allergies, particularly to cats and dogs.
2. Drugs and medicines
Certain medicines can cause allergic reactions. Common examples include some antibiotics, pain relievers, and other medications. Not every unwanted reaction to a medicine is a true allergy.
3. Foods
Common food allergens include:
- Milk
- Eggs
- Peanuts
- Tree nuts
- Fish
- Shellfish
- Wheat
- Soy
- Sesame
Food allergies can cause symptoms ranging from mild itching or hives to severe anaphylaxis.
4. Insect stings
Venom from insects such as bees, wasps, hornets, and fire ants can cause allergic reactions. Local swelling may occur, while some people can develop a serious systemic reaction.
5. Mold
Mold spores can trigger allergy symptoms, particularly affecting the nose, eyes, and respiratory system.
6. Plants
Pollen from trees, grasses, and weeds is a common cause of seasonal allergies, often known as hay fever or allergic rhinitis. Other common environmental allergens include house dust mites and certain occupational substances.
Several factors may increase the likelihood of developing allergies, including:
- A family history of allergies or allergic diseases
- Childhood or previous allergic conditions
- Asthma or allergic rhinitis
- Repeated exposure to certain allergens
- Certain environmental or occupational exposures
Having a family history of allergies does not mean that a person will necessarily develop the same allergy as another family member.
A healthcare professional will usually begin by asking about the person’s symptoms, their timing, possible triggers, medical history, and family history. Depending on the suspected allergy, testing may include:
A small amount of a suspected allergen is placed on or just beneath the skin. The area is then observed for a reaction. This test can help identify sensitivity to specific allergens.
Blood tests can measure specific IgE antibodies associated with particular allergens.
In selected cases, an allergist may recommend additional testing, including a medically supervised oral food challenge. Such testing should only be performed under appropriate medical supervision because it can provoke an allergic reaction.
Treatment depends on the type and severity of the allergy.
The most effective way to prevent many allergic reactions is to identify and avoid the triggering allergen whenever possible.
Depending on the symptoms, a doctor may recommend:
- Antihistamines
- Nasal corticosteroid sprays
- Other nasal allergy medicines
- Eye drops
- Inhaled medicines for allergy-associated respiratory symptoms
- Topical medicines for certain skin reactions
Medicines should be selected according to the individual’s condition and used as directed.
For some allergies, allergen immunotherapy may be recommended. It involves carefully controlled exposure to specific allergens over time to reduce sensitivity. It may be given as allergy shots or, for selected allergens, as tablets under medical supervision.
People who are at risk of anaphylaxis may be prescribed an epinephrine (adrenaline) auto-injector. They should be taught how and when to use it and should follow their doctor’s emergency action plan.
Although not all allergies can be prevented, the risk of reactions can often be reduced by:
- Identifying known allergens with the help of a healthcare professional
- Avoiding known triggers
- Reading food and medicine labels carefully
- Informing restaurants, schools, workplaces, and caregivers about serious food allergies
- Keeping prescribed emergency medicines readily available
- Following an allergy action plan
- Keeping indoor environments clean and reducing exposure to known environmental allergens
- Using appropriate protective measures when exposure to occupational allergens cannot be avoided
People with a history of severe allergic reactions should discuss an emergency plan with their doctor.
Consult a healthcare professional if allergy symptoms are frequent, persistent, interfere with daily activities, or are difficult to control. Medical evaluation is particularly important when the cause of a reaction is unclear or when symptoms involve breathing difficulties. Seek emergency medical care immediately if severe symptoms such as difficulty breathing, throat or tongue swelling, fainting, or signs of anaphylaxis occur.
Depending on the symptoms and suspected cause, the following specialists may be involved:
- Allergist
- Immunologist
- Pulmonologist, when significant respiratory symptoms are present
- Dermatologist, when allergic skin problems require specialist evaluation
An allergist/immunologist is the primary specialist for evaluating and managing many types of allergies.
An allergy is an abnormal immune response to a normally harmless substance known as an allergen.
Common triggers include foods, medicines, pollen, mold, animal dander, dust mites, and insect venom.
Yes. Some allergic reactions can cause coughing, wheezing, chest tightness, and shortness of breath. Severe reactions can cause life-threatening airway and breathing problems.
No. An allergy involves the immune system, whereas many food intolerances do not involve an immune reaction. For example, lactose intolerance is different from a milk allergy.
Yes. Allergies can develop at any age, even if a person previously tolerated a particular substance without problems.
Some allergies may become less troublesome over time, while others persist. Treatments such as allergen immunotherapy can reduce sensitivity to certain allergens, but they are not appropriate for every allergy.
Anaphylaxis requires immediate emergency treatment. If you have been prescribed an epinephrine auto-injector, use it according to your emergency plan and seek emergency medical care immediately.
