Quick Answer
Eczema (atopic dermatitis) and psoriasis are both chronic inflammatory skin conditions but have distinct characteristics. Eczema is intensely itchy, begins in childhood, worsens with allergens and irritants, and appears in flexural creases. Psoriasis produces well-defined scaly plaques, is less itchy, appears on extensor surfaces, and is driven by T-cell autoimmunity rather than IgE allergy.
Appearance: How They Look Different
Atopic dermatitis (eczema) presents as erythematous (red), weeping, oozing patches with indistinct borders. In acute phases, vesicles (tiny blisters) and crusting are common. In chronic phases, skin becomes lichenified (thickened with visible skin markings), hyperpigmented, and leathery from chronic scratching. Eczema lesions have soft, irregular edges and a dull, matte appearance.
Psoriasis presents as well-demarcated, raised plaques covered with silvery-white scale — the scale results from accelerated keratinocyte turnover (cells renew every 3–5 days instead of the normal 28). Plaques have sharp, clearly defined borders and a shiny, reflective appearance when scale is present. The Auspitz sign — pinpoint bleeding on removal of scale — is characteristic of psoriasis.
| Feature | Eczema (Atopic Dermatitis) | Psoriasis |
|---|---|---|
| Appearance | Red, weeping, ill-defined patches | Thick, silvery-scaled plaques |
| Location | Flexural creases (elbow, knee) | Extensor surfaces, scalp, nails |
| Itch severity | Intense, distressing | Moderate, sometimes absent |
| Age of onset | Usually infancy–childhood | Young adult to middle age |
| Trigger pattern | Allergens, irritants, S. aureus | Stress, infection, medications |
| IgE involvement | Yes — often elevated | No — T-cell autoimmune |
Location on the Body
Eczema characteristically affects flexural skin — the inner elbow crease, back of the knee, wrists, ankles, and neck — though in infants it often begins on the cheeks and scalp. Flexural distribution results from occlusion and friction in skin folds that worsen barrier damage and sweat retention.
Psoriasis classically affects extensor surfaces — the outer elbows, knees, and shins — as well as the scalp (often with distinct hairline involvement), lower back (sacrum), and nails (pitting, onycholysis, and oil spots are psoriatic nail changes). Inverse psoriasis affects skin folds (armpits, groin, under breasts) and lacks the silvery scale. Genital and nail involvement are more specific for psoriasis.
Causes and Immune Mechanisms
Eczema is part of the atopic march — it has strong IgE immune involvement, elevated total and specific IgE, skin barrier dysfunction (filaggrin deficiency), and Th2-dominant inflammation. It is frequently associated with asthma, allergic rhinitis, and food allergy in the same patient. Environmental allergens (dust mites, pets, pollen) and food allergens trigger flares.
Psoriasis is a T-cell-mediated autoimmune condition driven by Th1 and Th17 lymphocytes rather than Th2/IgE. Triggers include streptococcal infections (Koebner phenomenon), physical trauma, stress, certain medications (beta-blockers, lithium, NSAIDs, antimalarials), and alcohol use. Psoriasis has a strong genetic component (HLA-Cw6 is the strongest risk allele) and is associated with psoriatic arthritis, cardiovascular disease, and metabolic syndrome — conditions not associated with eczema.
Key Takeaways
- Eczema: ill-defined itchy patches in flexural creases; psoriasis: sharply bordered scaly plaques on extensor surfaces.
- Eczema is Th2/IgE-mediated (atopic); psoriasis is Th1/Th17 autoimmune (not IgE-related).
- Psoriasis nails show pitting and onycholysis; eczema does not typically affect nails.
- Eczema is associated with asthma and food allergy; psoriasis is associated with psoriatic arthritis and cardiovascular disease.
- Both conditions can be difficult to distinguish in clinical practice — a dermatologist should diagnose uncertain cases.
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