What causes eczema and can food allergies trigger it?

Causes of Eczema and the Role of Food Allergies

Food allergies can trigger or worsen eczema in susceptible individuals, particularly in children, but they are not the primary cause of eczema for most patients. 1

Understanding Eczema (Atopic Dermatitis)

Eczema, also known as atopic dermatitis, is a chronic, relapsing, pruritic inflammatory skin condition that develops through complex interactions between:

1. Genetic factors:

   • Skin barrier dysfunction genes (including SPINK5 variants) 1
   • Immune system regulation genes (including IL13 variants) 1

2. Environmental triggers:

   • Allergens (food and aeroallergens)
   • Irritants (soaps, detergents, household cleaners)
   • Climate factors (humidity, temperature)
   • Pollution and tobacco smoke exposure 1
   • Infections

3. Immune dysregulation:

   • Epithelial barrier disruption
   • Release of inflammatory cytokines (IL-25, IL-33, thymic stromal lymphopoietin) 1

Food Allergies and Eczema: The Connection

Prevalence and Association

• A fair number of children with eczema have food allergies, particularly those with:

  • Younger age
  • More severe disease 1
  • Early-onset eczema (before 3 months of age) 2

• Research shows that infants with eczema are:

  • 6 times more likely to have egg allergy
  • 11 times more likely to have peanut allergy compared to infants without eczema 2

Mechanism of Food-Induced Eczema Flares

Food allergies can trigger eczema flares through two main mechanisms:

1. IgE-mediated reactions (immediate, within 2 hours)
2. T-cell mediated responses (delayed, typically 6-48 hours later) 1, 3

Age-Related Patterns

• Infants and young children: Cow's milk and hen's eggs are common triggers
• Older children, adolescents, and adults: Aeroallergens and pollen-related foods become more important 3

Diagnostic Approach for Food-Related Eczema

When food allergies are suspected in a patient with eczema:

1. Consider testing when:

   • Child under 5 years has moderate to severe eczema that persists despite optimized management
   • There's a reliable history of immediate reaction after food ingestion
   • Both of the above are present 1

2. Appropriate testing includes:

   • Skin prick testing (SPT)
   • Serum-specific IgE testing
   • Note: Negative tests are helpful to rule out food allergy (>95% negative predictive value), but positive results only indicate sensitization and require clinical correlation 1

3. Avoid broad panel testing without clinical history of reactions, as this leads to overdiagnosis 1

Important Caveats

• Not all eczema is triggered by food allergies - many patients with eczema have no food allergies
• Positive allergy tests alone are insufficient for diagnosis - clinical correlation is essential 1
• Skin barrier dysfunction may be the primary mechanism allowing allergen sensitization (dual allergen exposure hypothesis) 1
• Food allergies may coexist with eczema without directly causing flares 1

Management Implications

For patients with confirmed food-triggered eczema:

• Targeted elimination of specific trigger foods
• Maintenance of skin barrier with emollients and appropriate bathing
• Topical anti-inflammatory treatments as needed
• Education about avoiding identified triggers

Conclusion

While food allergies can trigger eczema flares in some patients, particularly young children with moderate-to-severe disease, they are just one of many potential triggers. The relationship between eczema and food allergies is complex, with eczema itself being a risk factor for developing food allergies through compromised skin barrier function. Proper diagnosis requires careful clinical correlation of symptoms with test results rather than relying on allergy testing alone.