Allergies

Overview

An allergy is a condition in which the immune system overreacts to substances that are normally harmless. Things like pollen, house dust, certain foods, or pet dander cause no problems in most people. In someone with an allergy, however, the immune system identifies these substances as dangerous and activates its defenses. This response is what causes symptoms.

The immune system's job is to protect the body from real threats such as bacteria and viruses. In an allergy, it triggers a false alarm. Each time the immune system encounters a harmless substance it has become sensitized to, it produces antibodies specific to that substance and releases chemicals; most notably histamine. These chemicals cause symptoms such as a runny nose, itching, rashes, or shortness of breath.

Allergies are extremely common. A significant portion of the world's population experiences at least one type of allergy at some point in their lives. They can range from a mild nuisance to a life-threatening emergency. Most allergies cannot be cured, but with the right management, symptoms can largely be brought under control.

Types of Allergies

Allergies are categorized according to the trigger substance and the part of the body affected.

• Respiratory allergies. This is the most common type. Airborne particles such as pollen, dust mites, mold, and pet dander affect the nose and airways. Allergic rhinitis (hay fever) and allergic asthma fall into this group. Symptoms may be seasonal or may persist throughout the year.
• Food allergies. The immune system overreacts to certain foods. The most common food allergens include peanuts, tree nuts, milk, eggs, wheat, soy, fish, and shellfish. Food allergies can cause reactions ranging from mild digestive symptoms to serious anaphylaxis.
• Skin allergies. Allergic reactions can develop when the skin comes into contact with various allergens, or as a response to certain foods or medications. Eczema (atopic dermatitis), contact dermatitis, and urticaria (hives) fall into this group.
• Drug allergies. Some people develop allergic reactions to penicillin, aspirin, or other medications. Drug allergies can present in many ways, ranging from a rash to anaphylaxis.
• Insect sting allergies. These develop when the immune system overreacts to the sting of a bee, wasp, or ant. Most people experience only local swelling and pain, but in those with an allergy, serious systemic reactions and anaphylaxis can develop.
• Latex allergy. Latex, made from natural rubber, is found in gloves, balloons, and some medical supplies. In some people who are exposed to latex, skin rashes, itching, and in severe cases anaphylaxis can develop.
• Eye allergy (Allergic conjunctivitis). This develops when the membrane covering the eyelids and the white part of the eye reacts to allergens. Itching, redness, watering, and eyelid swelling are common symptoms. It is often seen alongside allergic rhinitis.

Symptoms

Allergy symptoms vary greatly depending on the trigger and the part of the body affected.

• Nose and airway symptoms. Runny nose, nasal congestion, sneezing, nasal itching, and a change in voice are common. In allergic asthma, shortness of breath, wheezing, and coughing are also present.
• Eye symptoms. Itching, redness, watering, and eyelid swelling can occur. These symptoms are particularly noticeable during pollen season.
• Skin symptoms. Itching, redness, hives, and eczema are the most common skin symptoms. In contact allergies, the rash appears only at the site of contact, while in other allergy types it can spread to different parts of the body.
• Digestive symptoms. In food allergies, nausea, vomiting, abdominal pain, and diarrhea may occur. In some people, itching or swelling in the mouth or lips is the first sign.
• Anaphylaxis. This is the most serious and potentially life-threatening allergic reaction. It usually develops within minutes. A drop in blood pressure, rapid heartbeat, severe shortness of breath, a feeling of throat tightening, confusion, and fainting can all occur. Anaphylaxis is a medical emergency and requires immediate intervention with an adrenaline injection.

When to See a Doctor or Go to the Emergency Room

• If symptoms are negatively affecting daily life or disrupting sleep, see an allergist.
• If over-the-counter medications are not controlling symptoms adequately, an evaluation should be done.
• If you experience a serious allergic reaction for the first time, see a doctor.
• If shortness of breath, throat swelling, or a drop in blood pressure develops, call emergency services immediately. These may be signs of anaphylaxis.
• If you have previously experienced anaphylaxis and have an epinephrine injector with you, use it right away and go to the emergency room.

Causes and Risk Factors

Why allergies develop in some people and not others is not fully understood. Genetic predisposition and environmental factors both play a role.

• Family history. Allergies have a strong hereditary component. If one parent has allergies, asthma, or eczema, the child's risk of developing an allergy is higher. If both parents are affected, the risk is even greater. It is worth noting that what is inherited is a general tendency toward allergic reactions, not necessarily the same specific allergy.
• Early exposure. Being exposed to a variety of microbes and environmental factors during the first years of life may help the immune system develop properly. Allergic conditions are thought to be more common in children who grow up in very sterile environments.
• Personal history of allergy or asthma. Having one type of allergy increases the risk of developing others. Children who have eczema or a food allergy are more likely to develop respiratory allergies later in life.
• Environmental factors. Air pollution, exposure to cigarette smoke, and certain chemicals may increase the likelihood of allergic sensitization.
• Age. Allergies can develop at any age but are more common in childhood. Some childhood allergies improve with age, while others persist into adulthood or can reappear later in life.

Diagnosis

Allergy diagnosis is based on a combination of medical history, physical examination, and testing.

• Detailed medical history. This is the foundation of the diagnosis. When and under what circumstances symptoms appear, what substances the patient has been in contact with, and family history are all assessed.
• Skin prick test. This is the most commonly used allergy test. Small amounts of various allergens are applied to the forearm or back, and the skin's reaction is evaluated after 15 to 20 minutes. A positive result indicates sensitivity to that substance. The test is quick, reliable, and allows multiple allergens to be assessed at the same time.
• Blood test (Specific IgE test). This measures the level of IgE antibodies against specific allergens in the blood. It is used when a skin test cannot be performed or to support the skin test results.
• Elimination diet. When a food allergy is suspected, specific foods are removed from the diet and any changes in symptoms are monitored. If symptoms resolve after elimination and return when the food is reintroduced, this supports the diagnosis.
• Provocation test. A small amount of the suspected allergen is given under controlled conditions. It is used particularly for food and drug allergies and is carried out under medical supervision.

Treatment

There is no definitive cure for allergies. However, avoiding triggers, medication, and immunotherapy can bring symptoms largely under control.

• Avoiding triggers. This is the most fundamental and effective approach. Knowing which substances cause an allergic reaction and staying away from them as much as possible significantly reduces symptoms. Complete avoidance is not always possible, however.
• Antihistamines. These are the most commonly used allergy medications. They block the effect of histamine (the chemical that drives the immune response) and relieve symptoms such as itching, runny nose, and watery eyes. Newer-generation antihistamines do not cause drowsiness and are suitable for daily use.
• Corticosteroids. These are powerful medications that suppress inflammation. They are available as nasal sprays, eye drops, creams, or tablets. They are widely used in allergic rhinitis and skin allergies.
• Decongestants. These are used to relieve nasal congestion. They are appropriate for short-term use.
• Epinephrine auto-injector (EpiPen). This is an emergency medication that people at risk of anaphylaxis must always carry. When anaphylaxis begins, it should be used immediately, followed by a visit to the emergency room.
• Immunotherapy (Allergy shots). This offers a long-term and potentially lasting solution. Gradually increasing doses of the trigger allergen are given at regular intervals, either by injection or as sublingual drops. Over time, the immune system becomes less reactive to the substance. Full effect generally develops over 3 to 5 years. It is successfully used for pollen, house dust mite, pet dander, and insect sting allergies.

Living with Allergies

Allergy is a chronic condition. Identifying triggers and taking the right precautions, however, can make a significant difference to daily quality of life.

• Learn your triggers. Which substances set off your symptoms? Tracking when and in which environments symptoms appear helps identify triggers. Allergy tests can provide important guidance here.
• Adjust your home environment. For those with dust mite allergies, washing bedding regularly, choosing hard flooring instead of carpets, and keeping humidity levels low can all help. For pet allergies, keeping animals out of bedrooms and ventilating frequently are useful measures.
• Take precautions during pollen season. On days when pollen counts are high, limiting time outdoors, showering after coming inside, and keeping windows closed can reduce symptoms.
• Be careful with food allergies. Read labels, inform restaurant staff about your allergy, and be aware of the risk of cross-contamination. People with serious food allergies should always carry an epinephrine injector, given the risk of anaphylaxis.
• Take your medications consistently. For those with seasonal allergies, starting medication before symptoms begin is far more effective than waiting until they appear.

Preparing for Your Appointment

What you can do:

• Note when and under what circumstances symptoms occur.
• List the substances you think may be triggering your symptoms.
• Mention any family history of allergies, asthma, or eczema.
• List all medications and supplements you are taking.
• Bring any previous allergy test results if available.
• Write your questions down in advance.

Questions you can ask your doctor:

• Which substances am I allergic to?
• How can I avoid my triggers?
• Is immunotherapy right for me?
• Should I carry an epinephrine injector?
• Which medications should I use to control my symptoms?
• How often do I need to be monitored?

Your doctor may ask you:

• When did the symptoms start and how often do they occur?
• Under what circumstances do they appear?
• Is there a family history of allergies or asthma?
• Have you ever had a serious allergic reaction?
• Do you have any pets?
• Are you exposed to dust, moisture, or chemicals at home or at work?
• What medications are you taking?