Allergy Testing for Eczema: When and Why You Might Need It

Eczema can be a debilitating condition that affects every area of a person’s life. And because triggers aren’t always easy to identify, patients can feel overwhelmed and frustrated with constantly having to rely on topical steroid prescriptions.

Eczema is often mistaken for dermatitis. However, it’s actually a specific type of dermatitis, which is a general term for skin inflammation. Eczema involves inflammatory, non-infectious skin reactions caused by various factors along with a person's increased genetic sensitivity. It is marked by fluid build-up between cells in the skin's outer layer, causing these cells to separate.

Certain types of eczema are caused or worsened by allergies; it’s important for clinicians to be able to identify allergy-related causes of eczema to properly diagnose and treat their patients.

In this article we’ll discuss subtypes of eczema that are caused or worsened by allergies including how to identify them through a patient’s symptoms and order the appropriate lab work. Then, we’ll cover how to interpret lab results for the most effective treatments.

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The Connection Between Eczema and Allergies

Atopic dermatitis is a specific type of eczema that is associated with immune dysregulation. It is closely linked to allergies, and it’s considered part of the “allergic triad,” which also includes asthma and allergic rhinitis.

Eczema and Atopic Dermatitis

Atopic dermatitis is a form of eczema that is closely linked to allergies. It’s characterized by a chronic, itchy, inflammatory skin condition along with immune dysregulation. It most commonly affects children but can also occur in adults.

It typically involves a relapsing pattern, characterized by periods of flare-ups and remissions. Atopic dermatitis is often associated with elevated immunoglobulin E (IgE) levels and may co-occur with other allergic conditions like asthma and allergic rhinitis.

It is also associated with other conditions including eosinophilic esophagitis, or allergic inflammation of the esophagus, an increased risk of infections, some mental illnesses like anxiety and depression, and cardiovascular disease.

People with atopic dermatitis often have a genetic predisposition that makes their immune system overreact to common allergens like pollen, dust mites, or certain foods. This overreaction leads to inflammation and itchy, irritated skin, characteristic of eczema.

Overview of the Atopic Triad: Eczema, Allergic Rhinitis, and Asthma

The atopic triad includes eczema (atopic dermatitis), allergic rhinitis (hay fever), and asthma, which commonly occur together due to shared genetic and immune factors causing hypersensitivity.

This progression, known as the “atopic march,” typically begins with atopic dermatitis in infancy, followed by food allergies, allergic rhinitis, and asthma, involving skin barrier dysfunction and immune dysregulation.

The Role of Allergens in Triggering or Worsening Eczema Symptoms

In sensitive (genetically susceptible) people, allergens can play a significant role in triggering or worsening eczema symptoms.

When someone with eczema comes into contact with allergens such as pollen, pet dander, or certain foods, their immune system may react strongly, causing inflammation, redness, and itchiness in the skin.

Histamine release is triggered by allergens and leads to itch-scratch cycles, which further aggravate eczema.

‍Specific allergens commonly linked to atopic dermatitis include wheat, egg, peanut, soy, dairy, cockroach or dust mite antigens, as well as house cat dander. Interestingly, early life microbial exposures such as endotoxin exposure, contact with farm animals, and dog ownership might offer protection against developing atopic dermatitis.

Other eczema triggers include emotional or physical stress; irritants such as certain fabrics, detergents, and shampoos; excessive sweating; contact with chlorine and other chemicals in swimming pools.

It is likely that exposure to multiple triggers simultaneously (e.g., dust, pets, and cold weather) is more likely to lead to eczema flare-ups.

When to Consider Allergy Testing for Eczema

While allergy testing is not always necessary to understand the root cause of eczema, in certain settings the right allergy testing can provide a shortcut to an improved quality of life for patients.

Persistent or Worsening Eczema Despite Standard Treatment

If eczema doesn't improve with conventional treatments (like moisturizers or topical steroids), allergy testing may identify specific allergens that are causing or worsening the condition, leading to more targeted and effective management.

Eczema with Clear Seasonal Patterns or Related to Environmental Exposure

Allergy testing is helpful when eczema flares occur at certain times of the year or in specific environments. These patterns indicate a link to airborne allergens (e.g., pollen or dust), which can exacerbate symptoms.

History of Allergic Reactions or Sensitivities Alongside Eczema

Patients with a history of allergic reactions (like hives, respiratory issues, or food allergies) are more likely to have eczema linked to these allergies. Testing can help confirm this connection for personalized care.

Cases Where Food Allergies or Contact Allergens are Suspected as Triggers

If there's a suspicion that certain foods or substances (such as soaps, fragrances, or metals) are causing eczema flare-ups, allergy testing can confirm the specific allergens involved.

Types of Allergy Tests for Eczema

Atopic allergies can be assessed in a variety of ways, generally by testing for IgE responses to specific allergens.

Skin Prick Test and Intradermal Testing

Skin prick tests are used to identify IgE-mediated allergens by introducing small amounts of allergens into the skin through tiny pricks. They are effective for detecting immediate hypersensitivity reactions to common allergens like pollen, pet dander, or dust mites.

These tests are recommended when allergic triggers are suspected to worsen eczema or when standard treatments fail. They provide quick results with minimal discomfort.

However, skin prick tests may not detect non-IgE mediated allergies or delayed-type hypersensitivity, which can also affect eczema. Intradermal testing is more sensitive, involving allergen injections under the skin, but it carries a higher risk of systemic reactions including anaphylaxis.

Blood Tests (Specific IgE Testing)

RAST (radioallergosorbent test) and ImmunoCAP are commonly used to measure the level of IgE antibodies in the blood that react to specific allergens. These tests measure the presence and amount of IgE antibodies that are specific to particular allergens, helping to identify potential triggers.

ImmunoCAP is considered a next-generation version of RAST, offering improved sensitivity, specificity, and a broader range of allergen testing capabilities.

Blood tests are useful when skin tests are impractical or risky, and they’re not affected by antihistamines. However, blood tests can be inaccurate in up to 60% of cases, necessitating interpretation by a healthcare professional.

Total IgE blood testing is also available. This assesses the total amount of IgE present, but it does not reveal specific allergens.

Patch Testing for Contact Allergens

Patch testing is used to identify allergens that cause delayed allergic reactions, which might be linked to eczema flare-ups. Typical allergens tested include nickel, fragrances, preservatives including formaldehyde, and other chemicals commonly found in personal care products and jewelry.

Small patches containing various allergens are applied to the skin, usually on the back, and left in place for 48 hours. The skin is then monitored for reactions by a dermatologist for an additional 24-72 hours.

Elimination Diets for Food Allergies

Elimination diets involve removing specific foods from the diet to identify which ones might be triggering eczema symptoms. Foods are systematically removed from the diet and then gradually reintroduced while closely monitoring the skin for changes in symptoms.

However, eczema symptoms can fluctuate naturally, making it difficult to identify specific food triggers. A flare-up may occur due to reasons unrelated to diet, or due to multiple factors including non-dietary environmental triggers, leading to misconceptions about food-related causes.

Guidance from a dietitian or allergist is advisable to ensure nutritional needs are met and to accurately interpret the results of the elimination diet.

How to Prepare for Allergy Testing

Stopping Antihistamines Before Testing

Antihistamines must be stopped before skin prick tests because they can suppress allergic reactions and lead to false-negative results. Typically, they should be discontinued one week before testing.

Antihistamines do not interfere with serum IgE testing or patch testing, as these tests do not depend on mast cell degranulation.

What to Expect During Each Test Type

Each test differs in what they test and the procedure to test:

Serum IgE Testing

A blood sample is taken to measure IgE antibodies using ELISA technology. This test is relatively non-invasive, no preparation is needed, and it’s unaffected by antihistamines. Serum IgE testing is suitable for those who can't undergo skin testing.

Skin Prick Testing

Allergens are applied to the skin, which is pricked to introduce them. Controls are used for accuracy.

Results are available in 15-20 minutes. Positive reaction appears as a red, raised wheal. Minor discomfort is possible. Antihistamines must be stopped one week before testing.

Intradermal Testing

Allergens are injected just under the skin using higher concentrations than skin prick tests.

Positive reactions cause wheals. This is more sensitive than skin prick tests but may cause more discomfort and it has a higher risk of anaphylaxis.

Patch Testing

Allergens on patches are placed on the back for 48 hours, then checked for delayed reactions.

Patch testing identifies delayed hypersensitivity allergens. Avoid wetting the area or sweating. Antihistamines do not affect results.

Elimination Diet

An elimination diet is a short-term dietary plan designed to identify food sensitivities and intolerances by removing specific foods that commonly cause reactions such as wheat, dairy, eggs, soy, peanuts, eggs, tree nuts, and shellfish.

The elimination diet is typically done in two phases:

Elimination Phase: suspect foods are removed from the diet for 4-6 weeks. This allows the immune system to calm an excessive response to these foods and reduces symptoms. During this phase, foods known to be inflammatory like processed foods, alcohol, and excess sugar, are also avoided.

Reintroduction Phase: in this phase, foods are gradually reintroduced one at a time over a few days while monitoring for any adverse symptoms including allergic responses and eczema flare ups. If symptoms arise, the problematic food is eliminated again for 3-6 months before attempting reintroduction.

Elimination diets should be implemented as temporary interventions, ideally under the guidance of healthcare professionals, to avoid nutritional deficiencies and ensure balanced nutrition.

Managing Anxiety or Concerns

Preparing mentally for the test can help, especially for children. Explaining what will happen in simple terms, bringing a favorite toy or book, and using relaxation techniques can ease anxiety during the procedure.

Understanding Allergy Test Results

The results will each have specific meanings:

Positive Reactions vs. Non-Reactions

A positive reaction on a skin prick test appears as a raised, red bump, indicating sensitivity to a particular allergen. A non-reaction suggests no sensitivity.

Blood tests measure the level of specific IgE antibodies, with higher levels indicating possible allergies.

Considering Results Alongside Medical History and Symptoms

Test results should be interpreted within the context of the patient’s medical history. Allergy test results are more meaningful when combined with medical history and current symptoms to confirm whether an allergen truly triggers eczema.

Tailoring an Eczema Management Plan

Dermatologists or allergists will use the results to create a personalized treatment plan which may include avoiding certain allergens, using specific medications, or other therapies to manage and reduce eczema flare-ups.

How Allergy Testing Can Influence Eczema Treatment

Allergy testing can provide targeted therapies to help tailor an individual’s eczema treatments.

Avoidance Strategies

Positive allergy tests help identify specific triggers to provide targeted avoidance, such as using dust mite covers or switching to hypoallergenic products.

However, guidelines do not recommend strict avoidance of common allergens (such as dust mites, pet dander or certain foods) unless specific sensitivities have been confirmed through testing and are shown to exacerbate atopic dermatitis.

Immunotherapy

Immunotherapy can reduce sensitivity to identified allergens, potentially improving eczema symptoms over time.

However, while both sublingual and injection immunotherapy (allergy shots) for managing eczema have shown some benefit, particularly in patients sensitized to dust mites, they are not routinely recommended at this time.

Dietary Changes

Some children with moderate to severe atopic dermatitis may have food allergies, although this is less common in adults; the connection between food allergies and eczema symptoms remains unclear. However, many functional medicine practitioners help their patients reduce flare ups using nutrition and other therapies.

Guidelines advise against avoiding foods without clear evidence of an allergy. Elimination diets should be used for confirmed, clinically relevant food allergies under the guidance of a medical professional.

These diets can help manage eczema but must be supervised to avoid nutritional deficiencies. Guidance and suitable replacement foods are necessary to avoid nutritional deficiencies while avoiding symptom-triggering foods.

If there's a history of food allergy or if standard treatments fail, testing for common allergens (milk, egg, wheat, soy, peanuts) is advised, particularly in children under five with persistent, moderate to severe eczema. Suspected allergies should be confirmed through controlled food challenges or short-term elimination diets (4-6 weeks).

Limitations of Allergy Testing for Eczema

While allergy testing has its place in eczema management, it also has some limitations.

Not All Cases Are Allergy-Related

Negative allergy tests do not rule out other possible triggers for eczema, such as stress or irritants.

False Positives

Allergy tests can show false positives in up to 60% of cases, leading to unnecessary restrictions that might not actually improve eczema.

A Holistic Approach Is Often Needed

Clinicians may combine test results with other treatment strategies including simple diet and lifestyle changes for effective eczema management.

For example, the following factors may help reduce the severity of eczema:

An anti-inflammatory diet rich in omega-3 fatty acids and antioxidants such as the Mediterranean diet may protect against asthma and atopic conditions, including eczema.

Reduce processed food intake: an analysis involving over 15,000 participants linked processed food consumption with a higher risk of atopic dermatitis.

Reduce stress: stress can cause or exacerbate eczema flare-ups.

Mindfulness and self-compassion: people with eczema who used mindfulness and self-compassion exercises for 13 weeks showed significantly greater improvements in skin disease-specific quality of life scores compared to the control group.

When to Talk to Your Doctor About Allergy Testing

People living with confusing or overwhelming eczema flare ups should consider allergy testing with their doctor.

Indications for Testing

Consider allergy testing if eczema flare-ups are unexplained or frequent; if they seem related to specific exposures; or if known allergens are present.

When Standard Treatments Fail

If conventional eczema treatments are not providing sufficient relief, testing might uncover hidden allergens that are contributing to symptoms.

Starting the Conversation

Ask your dermatologist or allergist about allergy testing options if you suspect certain triggers or if current treatments are not fully effective.