Psoriasis: Types, Triggers, and Evidence-Based Treatments

What Is Psoriasis?

Psoriasis is a chronic, relapsing-remitting inflammatory skin disease driven by dysregulated immune activity. T-cells and dendritic cells produce an excess of cytokines — particularly TNF-α, IL-17, and IL-23 — that accelerate the skin cell cycle from the normal 28–30 days down to 3–5 days. Immature keratinocytes accumulate faster than they can be shed, forming the characteristic thick, scaly plaques.

Psoriasis affects approximately 2–3% of the global population (around 125 million people) and is not merely a skin condition. It is a systemic inflammatory disease associated with psoriatic arthritis, cardiovascular disease, metabolic syndrome, depression, and reduced quality of life.

Types of Psoriasis

• Plaque psoriasis (psoriasis vulgaris) — 80–90% of cases. Well-demarcated, raised, red plaques covered with silvery-white scales, typically on the scalp, elbows, knees, and lower back.
• Guttate psoriasis — Small, drop-shaped lesions scattered over the trunk. Often triggered by streptococcal throat infection; more common in children and young adults.
• Inverse psoriasis — Smooth, shiny red patches in skin folds (groin, axillae, under breasts). The scale is minimal because friction keeps skin moist.
• Pustular psoriasis — Pus-filled blisters (sterile) surrounded by red skin. Can be localised (palms/soles) or generalised — the generalised form is a medical emergency requiring hospitalisation.
• Erythrodermic psoriasis — Widespread redness covering most of the body surface. Rare but serious; causes temperature dysregulation and protein loss.
• Nail psoriasis — Affects up to 50% of patients: nail pitting, onycholysis (nail detachment), oil spots, and subungual hyperkeratosis. Strongly associated with psoriatic arthritis.

Common Triggers

Psoriasis has a genetic basis (over 80 associated genetic loci, including HLA-Cw6), but triggers provoke flares:

• Stress — psychological stress is the most commonly reported trigger
• Infections — especially streptococcal throat infection (guttate psoriasis), and HIV
• Medications — lithium, beta-blockers, antimalarials, NSAIDs, rapid steroid withdrawal
• Skin injury (Koebner phenomenon) — cuts, burns, tattoos, sunburn can produce new lesions at injury sites
• Alcohol — heavy consumption worsens psoriasis and reduces treatment response
• Smoking — significantly increases severity and is linked to palmoplantar pustular psoriasis
• Obesity — adipose tissue produces pro-inflammatory cytokines; weight loss improves disease and treatment response

Assessment: The PASI Score

The Psoriasis Area and Severity Index (PASI) quantifies disease extent and severity (scale 0–72). A PASI >10 with significant quality-of-life impairment generally warrants systemic therapy. The Dermatology Life Quality Index (DLQI) captures psychosocial impact.

Treatment: Topical Therapy (Mild–Moderate)

• Corticosteroids — first-line; reduce inflammation and cell proliferation. Potency selected by body site (avoid high-potency on face/flexures).
• Vitamin D analogues (calcipotriol, calcitriol) — slow keratinocyte proliferation; often combined with steroids for synergistic effect
• Calcineurin inhibitors (tacrolimus, pimecrolimus) — second-line for facial and flexural psoriasis; no skin atrophy risk
• Coal tar — older but effective antipruritic and antiproliferative agent; useful for scalp psoriasis
• Tazarotene — topical retinoid; effective but irritating; used with steroids to improve tolerability

Treatment: Phototherapy (Moderate)

Narrowband UVB (NB-UVB) is the preferred phototherapy modality — administered 3× weekly in a phototherapy unit. Effective in 70–80% of patients. PUVA (psoralen + UVA) is more potent but increases skin cancer risk with long-term use.

Treatment: Systemic Therapy (Moderate–Severe)

• Methotrexate — weekly oral/subcutaneous anti-metabolite; effective and inexpensive; requires LFT monitoring (hepatotoxicity risk)
• Ciclosporin — fast-acting for acute flares; limited to short courses due to nephrotoxicity and hypertension
• Acitretin — oral retinoid; especially useful for pustular and erythrodermic psoriasis; teratogenic (contraceptive requirement)
• Apremilast — oral PDE4 inhibitor; well tolerated (no monitoring required); moderate efficacy; good for difficult-to-treat areas

Treatment: Biologics (Severe / Refractory)

Biologics are targeted therapies that block specific cytokines driving psoriasis inflammation. They achieve PASI 90 (90% clearance) in 50–70% of patients:

• TNF-α inhibitors (adalimumab, etanercept, infliximab, certolizumab) — first-generation biologics; effective for both skin and joints
• IL-12/23 inhibitor (ustekinumab) — durable responses with 12-weekly maintenance dosing
• IL-17 inhibitors (secukinumab, ixekizumab, bimekizumab) — currently the fastest and most complete clearance; bimekizumab (IL-17A/F dual block) achieves PASI 90 in ~90% at 16 weeks
• IL-23 inhibitors (guselkumab, risankizumab, tildrakizumab) — highly selective; durable responses; some maintain remission after drug holiday

Psoriatic Arthritis

Up to 30% of people with psoriasis develop psoriatic arthritis (PsA) — inflammatory joint disease causing pain, stiffness, and progressive joint damage. Nail psoriasis, scalp psoriasis, and inverse psoriasis are the strongest skin predictors. Early rheumatology referral is critical to prevent irreversible joint damage. Biologics treat both the skin and joint components simultaneously.