Atopic Dermatitis: The Topical Ladder and Flare Control

Two broken things at once: barrier and immune fire

Atopic dermatitis is not one disease but two failures that reinforce each other. The first failure is structural. The outermost layer of skin, the stratum corneum, is a brick wall — dead cells as bricks, lipids as mortar — and its integrity depends heavily on a protein called filaggrin, which helps flatten and glue the cells together and generates natural moisturising factors. Many patients carry loss-of-function mutations in the filaggrin gene, so the mortar is thin from birth. The wall leaks: transepidermal water loss rises, the skin dries and cracks, and allergens, irritants and microbes get in. The second failure is immunological. Behind that leaky wall sits a type-2 immune response driven above all by two cytokines, IL-4 and IL-13, which further degrade the barrier, drive the switch to IgE-mediated allergy, and — crucially — signal directly to nerves to produce itch. The two failures lock together: a poor barrier lets in triggers, the triggers stoke IL-4/IL-13, and IL-4/IL-13 damage the barrier further. This is the same type-2 axis that the Systemic Eczema chapter targets from the inside with dupilumab; here we fight it from the outside.

Two more players complete the picture. Itch is not a symptom bolted on to the disease — it is central to it. The itch-scratch cycle turns a mild flare into a chronic, thickened, lichenified plaque: scratching breaks the barrier, releases more inflammatory mediators, and provokes more itch, so the patient scratches more. And the broken, moist skin is readily colonised by Staphylococcus aureus, whose density rises with disease severity; its toxins act as superantigens that further inflame the skin and can tip a simmering eczema into frank infection. Keep these four elements in view — barrier, type-2 inflammation, itch, and microbes — because every rung of the topical ladder is aimed at one or more of them.

Rung one: emollients, the non-negotiable foundation

Nothing above this rung works well without it. Emollients (moisturisers) are the base of the entire ladder and the one therapy every patient uses every day, flare or no flare. Mechanistically they do two things: they occlude the surface to cut transepidermal water loss, and they deliver lipids and humectants that help re-point the barrier's mortar. Applied generously and frequently — far more than most patients think, in the order of hundreds of grams a week for widespread disease — they reduce flare frequency and the amount of steroid ultimately needed. The classic technique is "soak and seal": a short lukewarm bath or shower to hydrate the skin, then apply the emollient within a few minutes onto still-damp skin to trap that water in. Just as important is what to remove: ordinary soaps and detergents strip the remaining lipids and raise skin pH, so soap substitutes and fragrance-free washes replace them. As a rule, ointments (greasiest, most occlusive) suit dry, thickened skin; creams are more cosmetically acceptable for daytime and flexures; lotions are weakest. This foundation is the Foundations-of-the-barrier principle in action, and it never comes off the regimen — even when higher rungs are added.

Rung two: topical corticosteroids for the flare

When inflammation is active — redness, oozing, intense itch — emollients alone will not put out the fire. Topical corticosteroids are the first-line anti-inflammatory: they bind the glucocorticoid receptor and broadly suppress inflammatory gene transcription, calming the type-2 response, reducing itch, and letting the barrier heal. The art is matching potency to site and severity. Potency runs from mild (hydrocortisone) through moderate and potent up to very potent (clobetasol propionate). Thin, high-absorption skin — the face, eyelids, genitals, and flexural folds — takes only mild agents for short bursts, because that is exactly where atrophy, striae and telangiectasia appear if potent steroids are overused. Thick skin such as palms, soles and lichenified plaques needs potent or very potent agents to work at all. The clinical rhythm is: apply a sufficiently strong steroid once daily until the flare is genuinely controlled, then step down — to a weaker agent or to intermittent use — rather than stopping abruptly, which invites rebound. Used this way, in defined courses, topical steroids are remarkably safe; the harm comes from the extremes of either over-use on delicate sites or, far more commonly, the under-treatment driven by steroid phobia. The potency ladder and its adverse effects are covered fully in the Topical Corticosteroids chapter.

Rungs three and four: steroid-sparing topicals

For delicate sites and long-term maintenance, non-steroid anti-inflammatories fill the gap. Some skin cannot tolerate repeated steroids — the face, eyelids and flexures above all — and some patients need to hold disease down for months. Here the steroid-sparing rungs come in. Topical calcineurin inhibitors, tacrolimus and pimecrolimus, block calcineurin in T cells, preventing the dephosphorylation of NFAT and so shutting down transcription of the very type-2 cytokines that drive the disease. Critically, they cause no skin atrophy, which makes them ideal precisely where steroids are riskiest: the face and skin folds. Their characteristic downside is a transient burning or stinging on application in the first days, which usually settles. Newer non-steroids target the same fire by different routes: crisaborole is a topical PDE4 inhibitor — by blocking phosphodiesterase-4 it raises intracellular cyclic AMP and damps pro-inflammatory cytokine output — useful for mild-to-moderate disease. And ruxolitinib is a topical JAK inhibitor: because IL-4 and IL-13 signal through the JAK-STAT pathway, blocking JAK interrupts the type-2 signal right at the receptor, giving fast itch relief. The mechanistic detail of these classes is developed in the Calcineurin, PDE4 and JAK inhibitors chapter; what matters here is where they sit on the ladder — as the steroid-sparing options for sensitive sites and for keeping control once a flare is broken.

Proactive maintenance: treating the calm skin

The old model was reactive: wait for a visible flare, then treat it. The better model for recurrent disease is proactive maintenance. Certain sites flare again and again in the same place because subclinical inflammation persists there even when the skin looks calm. Proactive therapy applies a topical anti-inflammatory — a moderate steroid, or a calcineurin inhibitor — to those known trouble spots twice a week (often called "weekend therapy"), on top of daily emollients, to suppress that smouldering inflammation before it erupts. This markedly lengthens the flare-free interval and, counter-intuitively, reduces total steroid exposure over a year compared with repeatedly chasing full-blown flares. It is the topical embodiment of a principle that runs through chronic inflammatory disease: it is easier and safer to keep a fire out than to keep putting it out.

Adjuncts: wraps, microbes, and the itch itself

Around the core ladder sit several supporting measures — and one commonly misused drug class. For severe, resistant flares, wet-wrap therapy layers a diluted topical steroid or emollient under damp then dry bandages: the occlusion boosts drug penetration, cools and soothes the skin, and physically stops scratching, often breaking a bad flare over a few days. On the microbial side, overt bacterial infection (weeping, honey-crusting, sudden worsening) needs antibiotics against S. aureus, and for patients with frequent infective flares, dilute bleach baths (sodium hypochlorite) can lower staphylococcal density and reduce flares. One infection deserves special fear: eczema herpeticum, a disseminated herpes simplex infection over eczematous skin — monomorphic punched-out erosions, often with fever and a very unwell patient — which is a dermatological emergency needing prompt systemic aciclovir, not more steroid. These infections tie directly to the Skin Infections chapter. Finally, the itch. It is worth being clear-eyed about antihistamines: because atopic itch is driven largely by IL-4/IL-13 and neural pathways rather than histamine, non-sedating antihistamines do little for it. Their only real role is the sedating ones (for example at night) to help a scratching child sleep — a comfort measure, not a treatment of the itch mechanism. The genuine way to stop the itch is to fix what causes it: restore the barrier and quiet the type-2 inflammation.