• A chronic, inflammatory disorder commonly characterized by cutaneous erythematous plaques with silvery scale, and varying phenotypes and severity
  • Clinical phenotypes:
    • Plaque (vulgaris): most common variant (~80% of cases); well-demarcated, red plaques with silvery scale; symmetrically distributed commonly on the scalp, extensor surfaces, and trunk.
    • Guttate: <2% of psoriasis patients, usually in patients <30 years of age; presents abruptly with 1- to 10-mm droplet-shaped erythematous papules with fine scale over trunk and extremities; often preceded by group A β-hemolytic streptococcal infection 2 to 3 weeks prior. Most cases resolve spontaneously.
    • Inverse: affects intertriginous areas and flexural surfaces; pink-to-red plaques with minimal scale; absence of satellite pustules distinguishes it from candidiasis.
    • Erythrodermic: generalized erythema and scaling, affecting 90% of body surface area (BSA) or more; associated with desquamation; hair loss; nail dystrophy; and systemic symptoms such as fever, chills, malaise, lymphadenopathy, and/or high-output cardiac failure.
    • Pustular: sterile pustules; several forms including generalized pustular psoriasis, localized pustular psoriasis, and impetigo herpetiformis (in pregnancy); generalized type can result in life-threatening bacterial superinfections.
    • Nail disease: pitting, oil spots, and onycholysis; nails involved in 50% with psoriasis at diagnosis with lifetime incidence of 80–90% with cutaneous psoriasis; increased association with psoriatic arthritis.


Predominant age: two peaks of incidence between the ages of 20 to 30 years and 50 to 60 years


  • 3.2% prevalence in the United States
  • In the United States, the most commonly affected demographic group is non-Hispanic Caucasian.

Etiology and Pathophysiology

Psoriasis is a complex immune-mediated disorder with interactions between dendritic cells, T lymphocytes, neutrophils, and keratinocytes that results from a polygenic predisposition in the setting of environmental triggers; associated with relapsing flares related to systemic, psychological, infectious, and environmental factors


  • Genetic predisposition (polygenic)
  • 40% have psoriasis in a first-degree relative.
  • Multiple susceptibility loci contain genes involved in immune system regulation.
  • HLA-C*06 is most strongly correlated with early onset psoriasis.

Risk Factors

  • Family history
  • Obesity
  • Local trauma; local irritation (Koebner phenomenon)
  • HIV
  • Streptococcal infection
  • Stress (may contribute to exacerbation)
  • Medications (lithium, antimalarials, β-blockers, interferon, TNF-α inhibitors, withdrawal of steroids)
  • Smoking
  • Alcohol abuse
  • Dysbiosis of gut microbiota

General Prevention

Control cardiovascular risk factors. Avoid triggers including trauma, sunburns, smoking, and exposure to certain medications, alcohol, and stress. Avoid excess dietary saturated fats, simple sugars, and red meats.

Commonly Associated Conditions

  • Psoriatic arthritis
  • Seborrheic dermatitis
  • Obesity, metabolic syndrome, diabetes, chronic kidney disease
  • Cardiovascular disease, atherosclerotic disease
  • Nonalcoholic fatty liver disease (NAFLD)
  • Other autoimmune conditions: Crohn disease, ulcerative colitis, ankylosing spondylitis
  • Psychiatric/psychological conditions: depression, anxiety, suicidal ideation, poor self-esteem, emotional burden/anxiety, alcohol abuse, sexual dysfunction
  • Myopathy

There's more to see -- the rest of this topic is available only to subscribers.