Topical Psoriasis Therapy: Vitamin D Analogues, Steroids and the Classics
Psoriasis is a skin that is trying to heal a wound that was never there. The epidermis renews itself at a frantic pace, driven by an inflammatory signal it cannot switch off, and the result is the thick, silvery, stubborn plaque every clinician learns to recognise on sight. For most patients the first — and often the whole — answer is not a pill or an infusion but a cream. The topical shelf is old and new at once: vitamin D analogues that slow the racing skin, potent steroids that quiet the inflammation, and century-old tars and dithranol that still earn their place. Knowing which to reach for, and why, is the foundation on which every later escalation is built.
A 34-year-old man rolls up his sleeves reluctantly. On both elbows, across his knees, and hidden in his scalp are well-demarcated red plaques capped with thick silvery scale; scratch one and it flakes like candle wax, and a few pinpoint bleeding points appear beneath. He has had them for years and has tried "every moisturiser in the pharmacy." His disease covers perhaps four percent of his body — limited, by the numbers — but the plaques itch, crack, and embarrass him at work. He does not need an infusion or an immunosuppressant that demands blood monitoring. He needs the right combination of creams, used correctly, and a clear plan for what happens if they are not enough. In him you can see the whole logic of topical therapy: match the drug to the biology of the plaque, respect the limits of the skin you are treating, and know in advance the ladder you will climb if the disease outgrows the cream.
What a plaque actually is
Two things go wrong at once: the skin proliferates too fast, and an immune signal keeps driving it. In normal skin, a keratinocyte born in the basal layer takes about a month to travel up and shed. In a psoriatic plaque that journey collapses to a matter of days. The epidermis thickens (acanthosis), the cells never fully mature, and their nuclei are still visible in the surface scale (parakeratosis) — which is why the scale is so abundant and loose. But the runaway proliferation is a downstream effect, not the root cause. The engine is inflammation. Dendritic cells release IL-23, which drives a population of T-helper-17 (Th17) cells to pour out IL-17 and, alongside TNF-α, this cytokine storm is what commands the keratinocytes to multiply. Hold that axis in mind — IL-23 → Th17 → IL-17/TNF — because it is exactly the pathway the systemic biologics in the later Psoriasis chapters are built to interrupt. Topicals work further downstream, on the skin itself, but the same fire is what they are trying to put out.
Think of the plaque as a factory production line that has jammed on maximum speed. Vitamin D analogues walk over to the line's own controller and turn the speed dial back down — telling the keratinocytes to slow their division and finish maturing properly. Corticosteroids, meanwhile, don't touch the dial at all; they storm into the room and switch off the alarm bells — the inflammatory shouting — that were driving the line to run flat out in the first place. That is why the two work so beautifully together: one calms the machine, the other silences the signal ordering it to race.
First-line for limited plaques: vitamin D analogues
A vitamin, re-engineered into a proliferation brake. The vitamin D analogues — calcipotriol (calcipotriene), calcitriol, and tacalcitol — are the modern first-line topical for limited plaque psoriasis. They bind the vitamin D receptor (VDR) inside keratinocytes, a nuclear receptor that switches gene transcription; the effect is to slow the excessive proliferation, push the cells to differentiate and mature normally, and dampen the local T-cell inflammation. In other words they attack the plaque's core abnormality directly, without the baggage of a steroid. They are clean, do not thin the skin, and can be used long-term. Their two limits are worth remembering: they irritate — a stinging, red reaction, especially on the face and in flexures — and because they engage the same receptor as natural vitamin D, overuse can raise serum calcium. That link to calcium homeostasis and the VDR is developed fully in the Endocrine chapter; here it simply sets a ceiling on how much cream a patient may apply each week.
The workhorse: potent steroids and the fixed combination
Potent topical corticosteroids act fast: they suppress the inflammatory cytokines, constrict the dilated vessels that redden the plaque, and calm the itch. Used alone they are excellent at inducing remission but carry the familiar penalties of prolonged potent-steroid use — skin atrophy, telangiectasia, striae, and, on abrupt withdrawal, a rebound flare that can be worse than the original. The general principles of steroid potency, quantity (the fingertip unit), and safe tapering are set out in the Topical Corticosteroids chapter and apply here in full. The elegant solution that dominates real-world practice is the fixed combination of calcipotriol plus betamethasone dipropionate in a single once-daily gel, foam, or ointment. The two are genuinely synergistic and, better still, each offsets the other's main flaw: the steroid suppresses the calcipotriol-induced irritation, while the vitamin D analogue counters the steroid's tendency to thin the skin and lets clinicians use it for longer with less atrophy. It clears plaques faster than either component alone and has become the default workhorse for limited-to-moderate plaque psoriasis.
Vitamin D analogues: calcipotriol (Dovonex), calcitriol (Silkis), tacalcitol (Curatoderm). Fixed combination: calcipotriol + betamethasone dipropionate (Dovobet / Enstilar foam). Potent-to-superpotent steroids used in psoriasis: betamethasone dipropionate, mometasone, clobetasol propionate (Dermovate) for thick or scalp plaques. Topical retinoid: tazarotene (Tazorac). Classic agents: coal tar (many strengths and vehicles), dithranol/anthralin (short-contact). Keratolytic adjunct: salicylic acid, often compounded into a tar or steroid base to lift scale.
- Psoriasis = hyperproliferative epidermis driven by IL-23 → Th17 → IL-17/TNF inflammation.
- Vitamin D analogues (calcipotriol, calcitriol, tacalcitol) bind the VDR to slow proliferation and normalise differentiation — first-line for limited plaques.
- Their limits: local irritation and — with overuse — hypercalcaemia.
- Potent steroids act fast on inflammation but risk atrophy, telangiectasia, and rebound on withdrawal.
- The calcipotriol + betamethasone fixed combination is the workhorse — synergistic, and each offsets the other's main downside.
- Emollients underpin every regimen — they soften scale, reduce itch, and improve penetration of active drugs.
The classics that still earn their place
Long before receptors were named, dermatology treated psoriasis with tar and dithranol, and both survive because they work. Coal tar is anti-proliferative and anti-inflammatory; it slows the epidermal turnover and calms the plaque, and it remains genuinely useful — especially for the scalp and as a shampoo. Its drawbacks are cosmetic more than medical: it is messy, smells of the road, and stains clothes and skin, so adherence is the real enemy. Dithranol (anthralin) is even older and more effective for thick, stable plaques; it generates free radicals that inhibit keratinocyte proliferation. But it burns and inflames normal skin and stains everything a stubborn brown-purple, which is why it is used as short-contact therapy — applied to the plaque for a limited time then washed off, sparing the surrounding skin. Tazarotene, a topical retinoid, normalises keratinocyte differentiation through retinoic-acid receptors; it is effective but irritating, and is often paired with a steroid to make it tolerable. None of these is glamorous, but for the right plaque in the right place they remain valuable, steroid-sparing options.
Getting the drug in: keratolytics and emollients
The thickest plaque is a wall the active drug cannot cross. A dense cap of scale does two things: it looks and feels awful, and it physically blocks vitamin D analogues and steroids from reaching the living epidermis beneath. This is where keratolytics earn their keep. Salicylic acid dissolves the intercellular cement holding the corneocytes together, lifting the scale away; strip that barrier and the active drugs penetrate far better. It is often compounded into a tar or steroid preparation for exactly this reason — though note that salicylic acid can inactivate calcipotriol, so the two are not mixed in the same application. Underneath everything sits the humble emollient, the true foundation of all psoriasis care. Regular greasy moisturisers soften scale, relieve the itch and cracking, reduce the visible redness, and improve how well the medicated products work. Patients often underrate them, but an emollient used generously is doing real pharmacological work by restoring the barrier and reducing the irritant reactions that make active treatments hard to tolerate.
The single most common reason a "correct" topical regimen fails is not the drug — it is the site and the adherence. Psoriasis loves the awkward places: the scalp, where hair blocks creams and demands foams, gels, and tar shampoos; the flexures and face, where the skin is thin and potent steroids or calcipotriol sting and atrophy, so mild agents or calcineurin inhibitors are borrowed instead; and the nails, where almost nothing topical penetrates the plate reliably, making them notoriously hard to treat. Before you escalate to a systemic drug, always ask whether the patient was actually able to use the cream — messy, twice-daily, greasy regimens on visible skin fail on human nature long before they fail on pharmacology.
When topicals are not enough
Topical therapy has a hard ceiling. It is realistic only for limited disease — roughly a few plaques over a small body surface area. Once psoriasis becomes extensive, or lands in disabling sites like the palms, soles, and nails, or brings joint disease (psoriatic arthritis), creams alone become impractical and inadequate: no patient can meaningfully apply ointment to half their skin twice a day, and topicals do nothing for the joints. That is the trigger to escalate. The next rung is usually phototherapy (narrowband UVB) or a conventional systemic — methotrexate, ciclosporin, or acitretin — and beyond them the targeted biologics that block the very cytokines named at the start of this chapter: TNF-α inhibitors, and the newer, cleaner agents against IL-17 and IL-23. Those systemic and biologic strategies are the subject of the next Psoriasis chapters, where the IL-23/Th17 axis introduced here becomes the direct drug target. Topicals never disappear, though; even in patients on a biologic, they remain the tool for the last few stubborn plaques.
- Coal tar is anti-proliferative and anti-inflammatory — messy but effective, especially for the scalp.
- Dithranol (anthralin) is potent for thick plaques but burns and stains — used as short-contact therapy.
- Salicylic acid lifts scale to improve penetration but can inactivate calcipotriol if co-applied.
- Tazarotene (topical retinoid) normalises differentiation but irritates — often paired with a steroid.
- Site matters: scalp needs foams/gels, face and flexures need mild agents, nails resist topicals.
- Extensive disease, disabling sites, or joint involvement trigger escalation to phototherapy, systemics, and biologics.
- Using a potent or superpotent steroid continuously without a plan — leading to skin atrophy, telangiectasia, tachyphylaxis, and a rebound flare when it is stopped abruptly.
- Exceeding the weekly limit on vitamin D analogues or slathering them over large areas — risking hypercalcaemia from a drug patients assume is "just a vitamin."
- Applying an active drug onto thick scale and calling it a treatment failure — without a keratolytic and emollient first, the drug never reaches its target.
A patient with limited plaque psoriasis on the elbows and knees needs a topical that can be used long-term to control the plaques without thinning the skin, while limiting the irritation of a vitamin D analogue used alone. Which choice best fits?
- Psoriasis is a hyperproliferative epidermis driven by IL-23 → Th17 → IL-17/TNF inflammation; topicals are first-line for limited plaque disease.
- Vitamin D analogues (calcipotriol, calcitriol, tacalcitol) bind the VDR to slow proliferation and normalise differentiation — irritation and, if overused, hypercalcaemia are the limits.
- Potent steroids act fast but risk atrophy and rebound; the calcipotriol + betamethasone fixed combination is the synergistic workhorse where each offsets the other's downside.
- Coal tar, dithranol, salicylic acid, tazarotene and emollients still matter; extensive disease, hard sites, or joint involvement escalate to phototherapy, systemics, and IL-17/IL-23/TNF biologics.
- Rook's Textbook of Dermatology — Psoriasis: topical therapy.
- Wolverton SE. Comprehensive Dermatologic Drug Therapy — Vitamin D analogues, topical corticosteroids, tar and anthralin.
- Katzung BG. Basic & Clinical Pharmacology — Dermatologic pharmacology.
- NICE guideline CG153. Psoriasis: assessment and management.
- Menter A, et al. Joint AAD–NPF guidelines of care for the management of psoriasis with topical therapy. Journal of the American Academy of Dermatology.
- British National Formulary (BNF) — Topical preparations for psoriasis.
