Overview
Allergies are common and chronic conditions that are intertwined with immune system function.[1] The immune system is the body’s defense network, which normally fights off unwanted invaders like viruses, bacteria, and other infectious agents. During most allergic reactions, the immune system is responding to a false alarm and treats a generally harmless substance, like pollen, as a threat.
There are different types of allergies, including asthma, atopic dermatitis, and food allergies, but it is not uncommon for people who have allergies to be sensitive to more than one stressor.
Causes
The causes of allergies are complex, as both genetics and environmental factors contribute to their development. If you have a family history of allergies, you have an increased risk of developing allergies, but that does not mean you will develop them.
Allergic reactions can be caused by:
Contact (foods, latex, poisonous plants)
Injection (insect bites and stings)
Ingestion (drugs, foods, supplements)
Inhalation (dust, mold, pet dander, smoke, pollen)
Symptoms
Allergies can manifest in many ways, including asthma, itching, rashes, runny nose, sneezing, and swelling, and in varying degrees of severity, from mild irritation to anaphylaxis — a life-threatening reaction requiring immediate medical treatment.
The way allergies manifest depends on the exposure pathway, as shown below.
| EXPOSURE TYPE | SYMPTOMS |
|---|---|
Contact | Skin exposure: hives, rash, itching, blistering
|
Injection | Symptoms can vary widely, depending on the insect. Reactions can range from redness, general pain, swelling, and itching, to severe chest pain, throat swelling, and rash. |
Ingestion | Food exposure: Upset stomach, diarrhea, nausea, vomiting, metallic taste, coughing, wheezing, nasal congestion, trouble breathing, hives, tingling, itching, redness.
|
Inhalation | Sinus irritation, stuffiness, itching, cough, mucus. |
Diagnosis
Blood test
When the immune system perceives a threat, it produces antibodies called immunoglobulin E (IgE). A blood test can measure the amount of IgE antibodies present in the body. A small amount is normal, but a large amount can indicate an allergy.
Two types of IgE blood tests are commonly used: total and specific.
High total IgE levels can indicate you have an allergy.
The specific IgE test helps identify the specific allergen you are sensitive to.
Sometimes a complete blood count (CBC) test is used to measure eosinophil white blood cell levels. Eosinophil levels, which are normally under 500 cells per microliter (cells/mcL), can be elevated if you have allergies.
Skin test
An allergy skin test (scratch, skin prick, or patch test) is used to determine which specific allergens are causing an allergic reaction. The test involves exposing skin to the specific allergen using one of these methods:
Scratch/prick test, in which a liquid drop containing the allergen is placed on the skin. A light scratch or prick through each drop is administered to better expose the body to the allergen.
Intradermal test, in which a small amount of the allergen is injected just below the surface of the skin.
Patch test, in which an adhesive patch is worn on the skin for 48–96 hours, after which the medical provider removes the patch and checks for rashes and reactions.
An allergy to the tested substance may exist if the site of the skin test becomes red or swells during any of the above tests. The larger the reaction, the more likely there is an allergy. Commonly tested allergens include pollen, dust, molds, and some drugs. Food allergies are typically not diagnosed with skin tests, as they are more likely to cause anaphylactic shock.
Oral food challenge
Oral food challenges (OFCs) can be used to confirm the presence of a specific food allergy or to determine whether the allergy has resolved. The test involves eliminating the foods being tested from the diet for a period of time, followed by a medically supervised refeeding of the eliminated foods.
There are three main types of OFCs:
Open, in which both the participant and observer know what food is being tested.
Single-blind, in which only the observer knows what food is being tested. In these trials, the tested food may be concealed in a capsule and a placebo capsule may or may not be used as a control.
Double-blind and placebo-controlled, the gold-standard in food allergy diagnostics, in which both the participant and observer are blinded to the food being tested. At least two feedings occur and neither party knows which food is being tested in which feeding.
Unproven tests and misdiagnosis
Mail-order lab tests that can be shipped right to your door which claim to help you identify food allergies (i.e. causes an immune reaction) and intolerances (i.e. causes a digestive reaction) have become increasingly popular. However, many such tests rely on an unproven method — IgG blood tests, not to be confused with IgE blood tests, discussed above.
The Canadian Society of Allergy and Clinical Immunology (CSACI),[2] the European Academy of Allergy and Clinical Immunology (EAACI),[3], the National Institute of Allergy and Infectious Diseases (NIAID),[4] and the American Academy of Allergy, Asthma & Immunology (AAAI)[5] recommend against such tests, as they have not been shown to reliably or accurately identify food allergies or intolerances.[6]
Caution is also advised for the following tests and treatments for allergies, as they are either unproven or disproven.[4]
Applied kinesiology (muscle testing)
Basophil histamine release/activation
Cytotoxicity assays
Electrodermal test
Endoscopic allergen provocation
Facial thermography
Gastric juice analysis
Hair analysis
Lymphocyte stimulation
Mediator release assay (MRT-LEAP diet)
Provocation neutralization
Pulse testing
Another form of misdiagnosis can come from confusing flu and cold symptoms for allergies caused by airborne particles (pollen, dust, pet dander). While these symptoms share many similarities, the chart below can help you tell the differences.
| SYMPTOMS | COLD | FLU | AIRBORNE ALLERGY |
|---|---|---|---|
Fever | Rare | Usual, high (100–102 °F), sometimes higher. Lasts 3–4 days. | Never |
Headache | Uncommon | Common | Uncommon |
General Aches, Pains | Slight | Usual; often severe | Never |
Fatigue, Weakness | Sometimes | Usual, can last up to 3 weeks | Sometimes |
Extreme Exhaustion | Never | Usual, at the beginning of the illness | Never |
Stuffy, Runny Nose | Common | Sometimes | Common |
Sneezing | Usual | Sometimes | Usual |
Sore Throat | Common | Sometimes | Sometimes |
Cough | Common | Common, can become severe | Sometimes |
Chest Discomfort | Mild to moderate | Common | Rare, except for people with allergic asthma |
Adapted from NIH News in Health. Cold, Flu, or Allergy? Know the Difference for Best Treatment.
Treatments
An allergy treatment plan will vary based on allergy type and severity, but commonly includes medicines (antihistamines, bronchodilators, corticosteroids, allergy shots, nasal sprays, creams, and eye drops), avoiding the allergen, and lifestyle changes.
People who are at high risk of anaphylactic shock should take additional precautions, such as carrying epinephrine at all times. Consider discussing a specific treatment plan with your physician.
The table below displays an analysis of human studies and indicates which supplements may or may not affect allergies. While there is no cure-all supplement, some may aid in allergy control or symptom relief.
