Causes of Eczema (Atopic Dermatitis)
Eczema results from a complex interaction between genetic skin barrier defects, immune system dysregulation, and environmental triggers—not from a single cause. 1
Primary Genetic and Structural Causes
Two risk factors are consistently and strongly associated with developing atopic dermatitis: family history of atopy and loss-of-function mutations in the filaggrin (FLG) gene. 2 Approximately 70% of AD patients have a family history of atopic disease. 2
- Filaggrin mutations cause severe barrier dysfunction by increasing trans-epidermal water loss, altering skin pH, and promoting dehydration. 3
- These genetic changes fundamentally compromise the skin's ability to function as a mechanical barrier against toxins, UV light, and water loss. 4
- The pathophysiology involves barrier dysfunction combined with alterations in cell-mediated immune responses and IgE-mediated hypersensitivity. 3
Immune Dysregulation
The imbalance of Th2 to Th1 cytokines creates alterations in cell-mediated immune responses and promotes IgE-mediated hypersensitivity. 3
- This immune dysregulation interacts with epidermal gene mutations to disrupt the epidermis, causing intensely pruritic skin lesions. 5
- The disease involves both innate and adaptive immune pathway responses. 3
Environmental Triggers and Exacerbating Factors
Chemical and Irritant Exposures
Soaps and detergents strip natural lipids from already compromised skin, worsening dryness. 1
- Harsh alkaline detergents unfavorably alter the skin's pH, causing downstream changes in enzyme activity and triggering inflammation. 3
- Airborne formaldehyde, harsh detergents, fragrances, and preservatives can trigger disease. 3
- Environmental pollutants trigger responses from both innate and adaptive immune pathways. 3
Physical and Climate Factors
Extremes of temperature and irritant fabrics (such as wool) exacerbate symptoms. 1
- Patients living in humid climates or developing countries may manifest AD only after changing locale or following onset of respiratory allergies. 2
- In Taiwan, where warm and humid climates dominate, fungi represent a major risk factor for AD among aeroallergens. 2
Infectious Triggers
Bacterial colonization/infection, particularly Staphylococcus aureus, causes deterioration with crusting and weeping. 1
- Secondary bacterial infections represent a common complication requiring antistaphylococcal antibiotics. 5
Allergen Exposures
Food allergens represent the major allergic triggers of AD in early life, after which environmental aeroallergens play a critical role. 2
- Aeroallergens affect both occurrence and severity of AD. 2
- Food allergies affect approximately 11% of adults with atopic dermatitis. 1
Maternal and Prenatal Factors
Tobacco smoke exposure during pregnancy and early childhood is associated with increased risk of AD. 2
- Elevated maternal work stress and long working hours during pregnancy increase the risk of AD in young children. 2
- Exposure to perfluorinated chemicals and phthalates is positively correlated with serum IgE levels and AD development. 2
Common Pitfalls in Understanding Causation
- Do not assume a single cause: The development and phenotypic expression depend on complex interactions between genetic factors, environmental allergen exposure, and nonspecific adjuvant factors such as pollution, infections, and climate. 2
- Recognize heterogeneity: The disease shows great complexity in its heterogeneous presentation, clinical signs, and longitudinal trajectory, with or without comorbid conditions. 6
- Understand the itch-scratch cycle: Repeated scratching triggers a self-perpetuating cycle that significantly impacts quality of life, but this is a consequence rather than a primary cause. 5