Overview
Psoriasis is a chronic inflammatory skin condition causing thickened, scaly, red patches — most commonly on the elbows, knees, scalp, and lower back. It results from an overactive immune response that accelerates skin cell production. About 30% of people with psoriasis develop psoriatic arthritis. It follows a relapsing-remitting course and is associated with cardiovascular disease and metabolic syndrome.
How common is it?
Psoriasis affects approximately 2 to 3% of the UK population — around 1.8 million people. It can start at any age but most commonly presents between 15 and 35 (Type 1) or after 55 (Type 2).
Causes and risk factors
Psoriasis results from T-cell-mediated inflammation causing keratinocyte hyperproliferation. Genetic predisposition is triggered by environmental factors.
Common risk factors
- Genetic: HLA-Cw*0602 allele is the strongest genetic association; 30% familial risk
- Triggers: streptococcal throat infection (especially guttate psoriasis), stress, skin trauma (Koebner phenomenon), alcohol, smoking, beta-blockers, lithium, antimalarials
- HIV infection (dramatically worsens psoriasis)
- Obesity increases risk and severity
Symptoms
- Well-defined, raised, red plaques with silvery-white scale
- Dry, cracked skin that may bleed
- Itching, burning, or soreness
- Thickened, pitted, or ridged nails
- Scalp involvement: thick scaly patches beyond the hairline
- Guttate psoriasis: widespread small drop-like lesions, often triggered by streptococcal infection
- Pustular psoriasis: pus-filled blisters (rare)
- Erythrodermic psoriasis: widespread redness affecting most of the body (rare — medical emergency)
When to see a doctor
See a GP for new or worsening skin changes. Seek urgent hospital assessment for erythrodermic psoriasis (skin all over body red and inflamed) and for pustular psoriasis. Refer to rheumatology for joint pain or stiffness alongside psoriasis.
Diagnosis
Clinical diagnosis in most cases. Skin biopsy if uncertain. Distinguish from eczema, fungal infection, and lichen planus. PASI (Psoriasis Area and Severity Index) and DLQI (Dermatology Life Quality Index) quantify disease severity.
Treatments
Topical treatments
Mild-to-moderate: topical corticosteroids plus vitamin D analogues (calcipotriol) — combination product Enstilar or Dovobet is highly effective. Coal tar preparations for scalp disease. Dithranol for stubborn plaques.
Phototherapy (narrowband UVB)
NBUVB phototherapy 3 times weekly for 6 to 8 weeks clears psoriasis in 60 to 80% of patients. Very effective for widespread plaque and guttate psoriasis.
Methotrexate and ciclosporin
First-line systemic treatments for moderate-to-severe psoriasis. Methotrexate weekly oral/injectable; ciclosporin for rapid control. Regular blood monitoring required.
Biologic therapies
Anti-TNF (adalimumab, etanercept), anti-IL-17 (secukinumab, ixekizumab), anti-IL-23 (risankizumab, guselkumab) biologics produce PASI 90 responses (90% skin clearance) in 60 to 80% of patients. Anti-IL-17/23 agents are most effective currently approved treatments for plaque psoriasis.
Self-care and lifestyle
- Avoid identified triggers: alcohol, smoking, stress
- Moisturise regularly to reduce scale and itching
- Attend for streptococcal throat infections promptly — tonsillitis is a common psoriasis trigger
- Maintain a healthy BMI — obesity worsens psoriasis and reduces biologic efficacy
Prevention
Psoriasis cannot be prevented but triggers can be identified and minimised. Prompt treatment of streptococcal infections may prevent guttate psoriasis flares.