Causes of Eczema (Atopic Dermatitis)
Atopic dermatitis results from a complex interaction between genetic skin barrier defects, immune system dysregulation, and environmental triggers—not from a single cause. 1
Core Pathophysiologic Mechanisms
The disease arises from three interconnected pathways that work together to create the clinical picture of eczema:
Genetic Barrier Dysfunction
- Loss-of-function mutations in filaggrin (a key protein in skin barrier formation) are the most well-established genetic cause, leading to increased water loss, pH alterations, and skin dehydration 2, 3
- Multiple genes in the epidermal differentiation complex on chromosome 1q21 contribute to impaired barrier function 3, 4
- This barrier impairment allows allergens and irritants to penetrate more easily, perpetuating inflammation 4
Immune Dysregulation
- Imbalance favoring Th2 over Th1 immune responses drives the inflammatory cascade 2
- Elevated IgE levels and hypersensitivity reactions to environmental and food allergens result from this immune skewing 1, 2
- This immune dysfunction is central to both disease initiation and the chronic inflammatory state 4
Environmental Factors
- Soaps and detergents strip natural lipids from already compromised skin, worsening dryness 1, 5
- Harsh alkaline cleansers alter skin pH, triggering downstream enzyme changes and inflammation 2
- Environmental pollutants (airborne formaldehyde, fragrances, preservatives) activate both innate and adaptive immune pathways 2
- Extremes of temperature and irritant fabrics (wool) exacerbate symptoms 1
Specific Trigger Categories
Allergen-Mediated Triggers
- Food allergens (cow's milk, eggs, wheat, soy, peanuts in young children; tree nuts, shellfish, fish in older children) can trigger flares, particularly in children under 5 with moderate-to-severe disease 5
- Aeroallergens (house dust mites, pollens, animal dander, fungi) trigger flares especially in moderate-to-severe cases, often causing worse eczema on exposed surfaces 5
Infectious Triggers
- Bacterial colonization/infection (particularly Staphylococcus aureus) causes deterioration with crusting and weeping 1, 5
- Viral infections (herpes simplex) present as grouped, punched-out erosions 1, 5
Associated Comorbidities (Not Causes, But Related)
While not causative, these conditions share underlying mechanisms:
- Asthma occurs in 24.8% of adults with AD, with 3-fold increased risk compared to general population 1
- Allergic rhinitis frequently coexists, though the "atopic march" theory (AD leading sequentially to other atopic diseases) remains unproven 1
- Food allergies affect approximately 11% of adults with AD 1
Critical Clinical Pitfall
The most common mistake is assuming eczema has a single identifiable cause in an individual patient. 1, 2 The reality is that genetic predisposition creates vulnerability, immune dysfunction maintains inflammation, and multiple environmental factors act as triggers—all simultaneously. Treatment must address barrier repair, immune modulation, and trigger avoidance rather than searching for one "root cause" to eliminate.