Eczema (atopic dermatitis) guide: causes, triggers, and evidence-based treatment

Atopic dermatitis — commonly called eczema — affects roughly 10–20% of children and 2–10% of adults. It is a chronic, relapsing inflammatory skin disease that is not an allergy and not contagious. Here is the complete evidence-based guide.

What causes atopic dermatitis

The barrier dysfunction model

Atopic dermatitis begins with a defective skin barrier — specifically, loss-of-function mutations or reduced expression of filaggrin (FLG), a structural protein that is essential for:

Corneocyte maturation — filaggrin cross-links keratin fibers to form the compact, flattened corneocytes that make up the stratum corneum
Natural moisturizing factor (NMF) production — filaggrin breakdown products (amino acids, urocanic acid, PCA) are the primary components of NMF, the hygroscopic compounds that hold water inside the stratum corneum
Acid mantle maintenance — NMF components contribute to the acidic pH of the skin surface (optimal ~4.5–5.5) that inhibits pathogen colonization

When filaggrin is reduced or absent:
Corneocytes are poorly formed → gaps in the stratum corneum → increased TEWL (transepidermal water loss)
Reduced NMF → the skin cannot retain water despite adequate hydration
Elevated skin pH → serine proteases overactivate → further barrier degradation → more gaps
Environmental antigens (dust mite proteins, food proteins, microbes) penetrate through barrier gaps → sensitize immune cells in the dermis

The immune dysregulation

Once antigens penetrate the barrier, a Th2-skewed immune response amplifies the inflammation:

IL-4 and IL-13 (Th2 cytokines) drive IgE production and further suppress filaggrin synthesis — creating a self-amplifying cycle where inflammation worsens the barrier defect that drives inflammation
IL-31 directly activates itch-sensing neurons — the primary driver of itch in atopic dermatitis
IL-33 and TSLP from keratinocytes activate type 2 innate lymphoid cells and further amplify Th2 skewing

This is why atopic dermatitis is in the "atopic march" — the same Th2 immune bias underlies atopic dermatitis, allergic rhinitis, asthma, and food allergy. Most children with severe atopic dermatitis develop other atopic conditions.

Staphylococcus aureus colonization

S. aureus colonizes the skin of >90% of atopic dermatitis patients (vs ~20% of healthy skin). It worsens disease through:
Secreting proteases that directly degrade filaggrin and barrier lipids
Producing superantigens that massively amplify T-cell activation
Inducing Th2 skewing through its cell-wall components

Anti-S. aureus treatments (bleach baths) reduce disease severity — confirming the contribution of bacterial colonization to inflammation.

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The itch-scratch cycle

Itch in atopic dermatitis is not secondary to the rash — it is a primary neurogenic symptom driven by IL-31 and pruritogenic neuropeptides acting on itch-specific C-fibers. The cycle:

Neurogenic itch signal → scratching
Scratching → mechanical barrier trauma + increased allergen/antigen entry
More antigen exposure → more Th2 activation → more IL-31 → more itch
Disrupted sleep from nocturnal itch → stress → cortisol elevation → further Th2 skewing

Breaking the itch-scratch cycle is a core treatment goal — not just comfort, but a mechanism that reduces ongoing barrier damage and inflammation.

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Identifying and managing triggers

Atopic dermatitis is a chronic condition with flares triggered by exposures that further disrupt the already-compromised barrier or amplify immune activation:

Environmental:
Dust mites — the most common indoor allergen trigger; encasing mattresses and pillows in allergen-proof covers reduces exposure
Pet dander — cats more than dogs; consider trial pet removal to assess impact
Mold — increases spore count in high-humidity environments; dehumidifiers reduce load
Pollen — particularly in pollen-triggered periorbital or facial eczema

Contact irritants (not allergens — irritant contact dermatitis):
Soaps and detergents with high pH, surfactants, or fragrance
Wool and coarse synthetic fabrics (mechanical irritation)
Sweat (lactic acid and salt; shower promptly after exercise)
Chlorinated pool water (shower immediately and re-apply emollient after swimming)
Drool and food around the mouth in young children

Contact allergens (true type IV delayed hypersensitivity):
Nickel (jewelry, jeans buttons)
Fragrance compounds — patch testing identifies which specific compounds
Preservatives (methylisothiazolinone, formaldehyde-releasers)
Topical antibiotics (neomycin)
Rubber accelerators (latex gloves)

Systemic triggers:
Stress — activates the HPA axis → cortisol → Th2 shift; also reduces sleep
Heat and humidity changes
Infections (particularly S. aureus; also viral URIs in children)

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Treatment hierarchy

Foundation: emollient therapy

The most important treatment in atopic dermatitis — and the most underutilized.

Emollients do not treat inflammation; they restore the barrier that allows inflammation to perpetuate itself. Applied correctly, emollients:
Reduce TEWL by providing an occlusional lipid film
Maintain skin hydration between topical steroid applications
Reduce the frequency of flares requiring steroid use
Are safe for unlimited, indefinite use on all ages

Evidence: A 2014 RCT (Simpson et al.) showed that emollient therapy started in the first 3 weeks of life in high-risk neonates reduced development of atopic dermatitis by 50% at 6 months — demonstrating that barrier repair has a causal role in preventing sensitization.

Optimal emollient formulation: Creams and ointments over lotions (higher oil:water ratio; better occlusion). Products containing ceramides (ceramide NP, AP, EOP), cholesterol, and fatty acids replenish the specific lipids depleted in atopic dermatitis skin. CeraVe, Cetaphil, Vanicream, and prescription barrier repair creams are evidence-supported options.

Application timing: Within 3 minutes of bathing (the "soak and seal" method) — bathing rehydrates the stratum corneum; immediate emollient application traps that water before TEWL can remove it.

Topical corticosteroids (TCS)

Topical steroids remain the first-line anti-inflammatory treatment for atopic dermatitis flares:
Suppress keratinocyte cytokine production and T-cell activation in the dermis
Reduce erythema, itch, and lichenification within days of application
Used for active flares; not maintenance — use is cyclic (flare → TCS → remission → emollient only)

Steroid potency selection:
Mild (hydrocortisone 1%, 2.5%): Face, eyelids, skin folds — areas with high absorption
Moderate (triamcinolone 0.1%, mometasone 0.1%): Body, limbs
Potent (clobetasol 0.05%): Thick lichenified plaques on palms/soles; short courses only

Steroid phobia is the primary reason patients under-treat flares and allow chronic inflammation to produce lichenification and scarring. When used appropriately — correct potency, correct duration, with emollient — TCS are safe. Skin atrophy from TCS occurs with prolonged daily use of potent steroids, not from appropriate flare treatment.

Calcineurin inhibitors (TCI)

Tacrolimus (Protopic) and pimecrolimus (Elidel) — non-steroidal topical anti-inflammatories:
Inhibit calcineurin → block IL-2 and T-cell activation
No skin atrophy risk — appropriate for long-term use on face, eyelids, skin folds
Preferred for sensitive areas where TCS atrophy risk is a concern
Approved for ages 2+; the 2023 FDA label update removed the prior boxed warning (the cancer signal was not substantiated in long-term data)

Phosphodiesterase-4 inhibitors

Crisaborole (Eucrisa): Topical PDE4 inhibitor for mild-moderate atopic dermatitis; modest efficacy; approved 2016.

Roflumilast (Zoryve) 0.15% cream: Newer, more potent PDE4 inhibitor with better efficacy data than crisaborole; approved 2024.

Biologics: dupilumab (Dupixent)

Mechanism: Monoclonal antibody blocking the IL-4Rα subunit — simultaneously inhibits signaling of IL-4 and IL-13 (the central Th2 cytokines). This directly targets the upstream driver of atopic dermatitis.

Efficacy: In Phase 3 trials, ~36–44% of patients achieved clear or almost clear skin at 16 weeks; 50%+ EASI score improvement in ~75% of patients. The most effective systemic treatment available for moderate-severe atopic dermatitis.

Safety profile: Injection site reactions (early weeks), and conjunctivitis (10–15% of patients — likely a class effect related to IL-4/IL-13 role in conjunctival immunity). No meaningful immunosuppression-related infections.

Approved for: Adults and children ≥6 months (weight-based dosing for children). Approved for atopic dermatitis, asthma, eosinophilic esophagitis, and chronic rhinosinusitis with nasal polyps.

Newer biologics and JAK inhibitors

Tralokinumab (Adbry): Anti-IL-13 specific biologic; similar efficacy to dupilumab; SC injection Q2W.

Topical ruxolitinib (Opzelura): JAK1/2 inhibitor cream; approved for mild-moderate atopic dermatitis ages 12+. Rapid itch relief; no systemic exposure at topical doses.

Oral abrocitinib (Cibinqo), upadacitinib (Rinvoq): Oral JAK inhibitors for moderate-severe disease; highly effective but require labs monitoring and carry class-level cardiovascular/malignancy risk warnings.

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Adults vs. children

Children: Atopic dermatitis often presents on the cheeks and extensor surfaces; may improve with age. Emollient therapy and mild-moderate TCS are the foundation. Dupilumab approved from 6 months for severe disease.

Adults: More likely to involve the flexural creases, hands, and face. Often more chronic and lichenified. More likely to have concurrent contact allergies identified by patch testing. Same treatment hierarchy, with biologics and JAK inhibitors appropriate for moderate-severe disease.

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When to see a dermatologist

Atopic dermatitis not controlled with OTC emollients + mild TCS after 4–6 weeks
Frequent flares (3+ per year) requiring TCS
Any involvement of the face, eyelids, or hands that is persistent
Suspicion of contact allergy — patch testing requires a dermatologist
Consideration of prescription calcineurin inhibitors, biologics, or JAK inhibitors

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