Diagnosis of Food Allergy in Atopic Dermatitis

Diagnostic Approach

The American Academy of Dermatology recommends that extensive allergy testing should not be performed without a clear medical history, as positive results may only reflect sensitization rather than true allergy 1, 2
Limited food allergy testing (for milk, eggs, wheat, soy, and peanuts) should be performed in children under 5 years old with moderate to severe and persistent atopic dermatitis despite optimal topical treatment, according to the American Academy of Dermatology 1, 3
The skin prick test is a useful diagnostic tool that measures immediate type I reactions, with a high negative predictive value (>95%) but a lower positive predictive value (40-60%), as stated by the American Academy of Dermatology 2, 4
Specific IgE testing for food allergens can be used as an alternative to skin prick testing, especially in cases with widespread skin lesions or marked dermatographism, as recommended by the American Academy of Dermatology 2, 4

Diagnostic Confirmation

The American Academy of Dermatology advises against starting an elimination diet based solely on the presence of atopic dermatitis or a suspected history, and instead recommends a stepwise approach including initial testing and subsequent dietary elimination and challenge 5, 6
A diagnostic elimination diet should be performed for 4-6 weeks, followed by an oral food challenge under medical supervision to confirm the diagnosis, as suggested by the American Academy of Dermatology 5, 6
The double-blind, placebo-controlled food challenge (DBPCFC) is considered the gold standard for diagnosing food allergy, according to the American Academy of Dermatology 3

Important Considerations

Prolonged and multiple elimination diets can be harmful, leading to weight loss, growth delay, calcium deficiency, and other nutritional deficiencies, as warned by the American Academy of Dermatology 5
Most children with food allergies develop tolerance over time, and regular re-evaluation is necessary, as stated by the American Academy of Dermatology 7
Effective treatment of atopic dermatitis remains skin care and topical therapies, even in the presence of confirmed food allergy, as emphasized by the American Academy of Dermatology 7

Diagnostic Approach for Suspected Food Allergy in Atopic Dermatitis

Initial Testing Strategy

Children under 5 years with moderate-to-severe atopic dermatitis that persists despite optimized topical treatment should be considered for limited food allergy testing, as recommended by the American Academy of Pediatrics 8
Testing is also indicated if there is a reliable history of immediate reaction after ingesting a specific food, according to the American Academy of Pediatrics 8

Critical Next Steps After Testing

An oral food challenge under allergist guidance is essential to confirm the diagnosis, as improvement during elimination may be coincidental or placebo effect, as stated by the Mayo Clinic Proceedings 9

Critical Pitfalls to Avoid

Often, avoidance is prescribed and no treatment for the underlying atopic dermatitis is provided, which is incorrect management, as noted by the Mayo Clinic Proceedings 10
Optimize topical corticosteroid therapy and ensure adequate emollient use before attributing all symptoms to food allergy, as recommended by the Journal of Microbiology, Immunology and Infection 11

When to Refer to Allergist

Referral to an allergist is recommended for longitudinal care, diagnostic testing, formulation of emergency anaphylaxis action plan, and supervised oral food challenges, as stated by the Mayo Clinic Proceedings 9
The allergist will help facilitate proper elimination diets under specialist supervision and prevent unnecessary dietary restrictions, as noted by the Mayo Clinic Proceedings 9 and 10

Diagnostic Approach for Suspected Food Allergy in Atopic Dermatitis

Initial Assessment and Diagnostic Algorithm

The American Academy of Dermatology recommends optimizing topical therapy before attributing symptoms to food allergy, ensuring appropriate-potency topical corticosteroids and adequate emollient use, as many children have inadequately treated atopic dermatitis, not food allergy 12
In children under 5 years with moderate-to-severe atopic dermatitis that persists despite optimized topical treatment, consider limited testing for milk, eggs, wheat, soy, and peanuts, as up to 37% of children younger than 5 years with moderate-to-severe atopic dermatitis have IgE-mediated food allergy 13

Diagnostic Testing and Food Challenge

Allergy testing, such as skin prick testing and food-specific IgE, has poor positive predictive value (40-60%) and only indicates sensitization, not true food allergy, and should be followed by supervised oral food challenge to confirm the diagnosis 14
Food allergy is a potential cause in only 35% of children with moderate-to-severe atopic dermatitis, and effective treatment of atopic dermatitis remains skin care and topical therapies, even in the presence of confirmed food allergy 14

Food-Triggered Eczema Flares

Pathophysiology and Diagnosis

Food can directly trigger eczema flares in a subset of patients, particularly in young children with moderate-to-severe disease, though this occurs in only about 35% of affected children and is less common in adults 15
The American Academy of Dermatology recommends considering limited food allergy testing only when a child is under 5 years old with moderate-to-severe atopic dermatitis, disease persists despite optimal topical management and adequate emollient use, and there is a reliable history of immediate allergic reaction after food ingestion 15
Immediate hypersensitivity (type I) reactions to foods can occur in patients with eczema, ranging from contact urticaria to anaphylaxis 16, 17
The American Academy of Dermatology suggests keeping a food diary to identify consistent correlations between symptoms and food intake, and to look for immediate reactions versus delayed effects occurring 2-4 days after exposure 15
A diagnostic elimination diet (4-6 weeks) can be used to confirm the diagnosis of food-triggered eczema flares, but only if there is consistent correlation of symptoms with or without positive testing 15
Supervised oral food challenge is essential to confirm diagnosis, as improvement during elimination may be coincidental or placebo effect, and to evaluate skin status with an established score (SCORAD or EASI) at 24 hours and later 15

Management and Prevention

The American Academy of Dermatology recommends avoiding multiple dietary restrictions and long-term avoidance without documented, clinically relevant food allergies, as this leads to weight loss, poor growth, calcium deficiency, hypovitaminosis, and kwashiorkor 15
Referral to an allergist is essential for longitudinal care, formulation of emergency anaphylaxis action plan, supervised oral food challenges, and prevention of unnecessary dietary restrictions, although this is not directly cited, the previous fact about the academy's recommendation is 15

Diagnostic Approach for Suspected Food Allergy in Atopic Dermatitis

Initial Assessment and Screening

The American Academy of Dermatology recommends asking parents to keep a food diary for one month to establish temporal correlation between food intake and eczema flare-ups in children with atopic dermatitis 18
The American Academy of Dermatology suggests performing limited testing for common allergens such as cow's milk, eggs, wheat, soy, and peanuts using skin prick testing or specific IgE levels in children under 5 years with moderate-to-severe atopic dermatitis 19

Diagnostic Testing

Skin prick testing or specific IgE levels have high negative predictive value (>95%) but poor positive predictive value (40-60%), meaning negative results effectively rule out food allergy, but positive results only indicate sensitization, not true allergy, according to the American Academy of Dermatology 19
The Mayo Clinic recommends avoiding broad panel allergy testing without clear clinical history, as positive results may only reflect sensitization rather than true allergy, and avoiding prescribing avoidance without treating the underlying atopic dermatitis 18

Prevalence and Referral

Food allergy is relevant in only 35% of children with moderate-to-severe atopic dermatitis, according to the Mayo Clinic Proceedings 18

Diagnostic Confirmation of Food Allergy in Atopic Dermatitis

Interpretation of IgE and Skin Prick Test Results

Positive food‑specific IgE (≥ 0.35 kU/L) or a skin‑prick test wheal (≥ 3 mm) must be correlated with the patient’s clinical history and confirmed by a supervised oral food challenge; the tests alone do not establish true allergy. 20
According to the National Academies consensus report (2017), equating a “positive test result” with the presence of a food allergy is a serious misconception and should be avoided. 21

Optimizing Dermatologic Therapy Before Allergy Evaluation

The American Academy of Dermatology advises that, prior to attributing dermatitis symptoms to food allergy, children should receive optimized topical therapy, which includes the use of appropriate‑potency corticosteroids and adequate emollient application. (Evidence from a 2005 Journal of Allergy and Clinical Immunology study) 22

Requirements for Supervised Oral Food Challenge

A supervised oral food challenge must be performed under allergist guidance with emergency equipment on hand; the protocol starts with minute amounts of the suspect food and is stopped at the first appearance of symptoms. (2005 JACI) 22
The same source states that the supervised oral food challenge is the only definitive method to confirm the clinical relevance of a suspected food allergy in patients with atopic dermatitis. 22