What is Eczema (Atopic Dermatitis)?
Eczema, synonymous with atopic dermatitis (AD), is a chronic, intensely pruritic inflammatory skin disease characterized by recurrent eczematous lesions, epidermal barrier dysfunction, and immune dysregulation, most commonly beginning in early childhood but potentially affecting individuals throughout their lifespan 1, 2.
Core Disease Characteristics
Atopic dermatitis manifests as a relapsing-remitting condition with several defining features:
- Pruritus is the hallmark symptom - the itch is often severe enough to create a self-perpetuating itch-scratch cycle that significantly impacts quality of life 1, 3
- Skin barrier dysfunction - disrupted epidermal integrity leads to increased water loss and susceptibility to irritants and allergens 2, 4
- Immune dysregulation - predominantly type-2 T-cell driven inflammation (Th2/Tc2), though multiple immune pathways including Th1, Th17, and Th22 are involved 2, 5
- Elevated IgE levels - often present with IgE-mediated sensitization to food and environmental allergens 1, 6
Clinical Presentation
The morphology varies by age and chronicity:
Acute lesions present with erythematous papules and vesicles, excoriations, oozing, and crusting 1, 6. The acute phase shows spongiosis histologically with overproduction of hyaluronic acid 5.
Chronic lesions demonstrate lichenification (thickened, leathery skin), hyperpigmentation, and xerosis (dry skin) 1, 6, 5. Chronic changes involve dermal fibrosis mediated by periostin 5.
Key morphological features include the "eczema triangle" describing polymorphism - composition of erythema, papules, seropapules, vesicles, scales, and crusts arising from multiple pinpoint foci 5.
Epidemiology and Natural History
- 60% develop disease in the first year of life, 90% by age 5 years 1
- Onset typically occurs between 3-6 months of age 1
- While most cases resolve by adulthood, 10-30% persist into adulthood, and some patients first develop symptoms as adults 1
- Affects approximately one in 10 people during their lifetime 3
- Represents the leading cause of global burden from skin disease 2
Pathophysiology
The disease arises from complex interactions:
Genetic factors - Strong genetic predisposition with mutations in filaggrin (a key epidermal differentiation protein) identified in early-onset and severe AD 2, 6. The epidermal differentiation complex on chromosome 1q21 contains multiple susceptibility loci 6.
Barrier dysfunction - Epidermal gene mutations and environmental factors disrupt the skin's mechanical barrier function against toxins, UV light, and water loss 7, 4.
Immune dysregulation - Type-2 mechanisms dominate but increasing evidence shows multiple immune pathways contribute to inflammation 2.
Associated Conditions and Comorbidities
Patients face increased risk of multiple comorbidities:
- Atopic comorbidities: food allergy, asthma, allergic rhinitis (the "atopic march") 2, 7
- Nonatopic comorbidities: autoimmune conditions, mental health disorders (anxiety, depression, sleep disturbance), cardiovascular disease 2, 7, 5
- Infectious complications: increased susceptibility to bacterial (particularly Staphylococcus aureus) and viral superinfections due to barrier dysfunction 7, 6
Diagnosis
Diagnosis is made clinically based on history, morphology, distribution of lesions, and associated signs 1. The 1980 Hanifin and Rajka criteria require 3 of 4 major criteria plus 3 of 23 minor criteria, though this is unwieldy for clinical practice 1. The UK Working Party distilled these into a more practical core set for clinical use 1.
Disease Burden
The psychosocial impact is substantial:
- Significant sleep disturbance from nocturnal pruritus 7, 8
- Social stigmatization and relationship difficulties 4
- Anxiety, hyperactivity, and depression 4
- Profound impact on patient and family quality of life 1, 8
Important Clinical Pearls
Common pitfall: Assuming all children outgrow AD - while many do improve, a significant minority (10-30%) continue to have disease into adulthood 1, 7.
Recognition in skin of color: Clinicians should recognize that rash morphology may differ in patients with darker skin tones, presenting with variations beyond classic dermatitis patterns 7.
Family history matters: A notable predictor of AD is family history of atopic disease, which should be elicited during evaluation 7.