An allergy occurs when the immune system reacts to a substance that is usually harmless to most people. These substances, known as allergens, can include pollen, dust mites, pet dander, foods, insect venom and some medicines.
The reaction can affect the nose, eyes, skin, airways or digestive system. Symptoms range from mild irritation to a severe reaction known as anaphylaxis, which can be life-threatening.
What causes allergies?
During an allergic reaction, the immune system mistakenly identifies a normally harmless substance as a threat and mounts a response against it.
Common allergens include pollen, house dust mites, animal dander, certain foods, insect stings and some medicines. The symptoms and their severity can vary from one person to another.
Hay fever, also called allergic rhinitis, is one common form of allergy. It can cause sneezing, a runny or blocked nose, itchy or watery eyes and coughing.
Allergies can also contribute to asthma symptoms in some people. But not every case of asthma or sinusitis is caused by an allergy.
How can you tell if you have an allergy?
Allergy symptoms can include sneezing, a runny or blocked nose, itchy or watery eyes, skin rashes or hives, coughing, wheezing, shortness of breath and, in some cases, stomach cramps, vomiting or diarrhoea.
Having one or more of these symptoms does not necessarily mean you have an allergy. Other conditions can produce similar symptoms, so a healthcare professional may need to assess the person’s medical history and symptoms before making a diagnosis.
Doctors may ask when the symptoms occur, what the person has been exposed to and whether particular foods, medicines, animals, pollen or other substances appear to trigger a reaction.
Allergy testing may also be used. Common tests include skin-prick testing and blood tests that look for specific IgE antibodies. Test results need to be interpreted alongside a person’s symptoms and medical history because a test result alone does not necessarily establish that an allergen is responsible for the symptoms.
How are allergies treated?
The first step in managing an allergy is usually to identify and avoid the substance that triggers the reaction where possible.
Treatment depends on the type and severity of the allergy. Medicines such as antihistamines and nasal sprays may help control some symptoms. For some people with persistent or severe allergies, doctors may recommend immunotherapy, which gradually exposes the person to controlled amounts of a specific allergen under medical supervision.
People with dust-mite allergies may benefit from measures that reduce exposure, including regularly washing bedding and reducing dust in the home. A vacuum cleaner with a HEPA filter can also help reduce airborne particles.
For people with pollen allergies, reducing exposure during periods of high pollen can help. Keeping windows and doors closed when pollen levels are high, cleaning after spending time outdoors and regularly vacuuming can reduce exposure.
Saline nasal sprays or rinses may also help some people with nasal allergy symptoms by clearing mucus and irritants from the nose.
When should you see a doctor?
People with recurring symptoms they believe may be caused by an allergy should speak with a healthcare professional, particularly if symptoms are interfering with daily activities or do not improve with usual treatment.
A specialist in allergies and immune-system disorders, known as an allergist, may be involved when the cause is unclear, symptoms are difficult to control, or a person has had a serious allergic reaction.
What is a severe allergic reaction?
Some allergies can cause anaphylaxis, a severe reaction that can develop rapidly after exposure to an allergen.
Symptoms can include difficulty breathing, swelling of the throat or tongue, dizziness or fainting, a rapid or weak pulse, hives and a sudden drop in blood pressure. Common triggers include certain foods, medicines and insect stings.
Anaphylaxis requires emergency medical treatment. Epinephrine, also called adrenaline, is the first-line treatment, and anyone experiencing a severe allergic reaction should receive emergency medical care. Even when symptoms improve after epinephrine, further medical assessment is needed because symptoms can return.
Can allergies be prevented?
There is no single way to prevent all allergies. Once a person’s triggers are identified, avoiding them where possible can reduce the likelihood of a reaction.
People trying to identify their triggers can keep a record of when symptoms occur and what they were exposed to at the time. This information can help a healthcare professional determine whether allergy testing or other investigations are appropriate.
Allergies are common, but they are not something that should be self-diagnosed solely from a symptom or an allergy-test result. Proper assessment can help distinguish an allergy from other conditions and determine the appropriate treatment.
