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Last reviewed: June 2023

Author(s): Dr Chelsea Jones, Newcastle, Australia; Dr Monisha Gupta, Dermatologist, Australia (2020); updated by Dr Salim Uddin, Medical Registrar, New Zealand; A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand (2023).

Reviewing dermatologist: Dr Ian Coulson

Edited by the DermNet content department


What is psoriasis?

Psoriasis is a chronic inflammatory skin condition characterised by clearly defined, red and scaly plaques. It is classified into several types.

Who gets psoriasis?

Psoriasis affects 2–4% of males and females. It can start at any age including childhood, with onset peaks at 15–25 years and 50–60 years. It tends to persist lifelong, fluctuating in extent and severity. It is particularly common in Caucasians but may affect people of any ethnicity. About one-third of patients with psoriasis have family members with psoriasis.

What causes psoriasis?

Psoriasis is multifactorial. It is classified as an immune-mediated genetic skin disease.

This involves a complex interaction between the innate and adaptive immune systems.

Genome-wide association studies report that the histocompatibility complex HLA-C*06:02 (previously known as HLA-Cw6) is associated with early-onset psoriasis and guttate psoriasis. This major histocompatibility complex is not associated with psoriatic arthritis, nail psoriasis, or late-onset psoriasis. 

Immune factors and inflammatory cytokines (messenger proteins) such as IL1β and TNFα, IL-23, and IL-17 are responsible for the clinical features of psoriasis. These have therefore become targets for biological drugs and have led to success in drug management.

What are the clinical features of psoriasis?

Psoriasis usually presents with symmetrically distributed, red, scaly plaques with well-defined edges. The scale is typically silvery white, except in skin folds where the plaques often appear shiny with a moist peeling surface. The most common sites are the scalp, elbows, and knees, but any part of the skin can be involved. The plaques are usually very persistent without treatment.

Itch is mostly mild but may be severe in some patients, leading to scratching and lichenification characterised by thickened leathery skin and increased skin markings. Painful skin cracks or fissures may occur, particularly on the palms and soles.

Psoriasis can demonstrate the Koebner phenomenon. This involves the generation of new lesions on the skin that has been damaged or irritated such as by injury, burns etc.

When psoriatic plaques clear up, they may leave brown or pale marks (postinflammatory hypo- or hyperpigmentation) that can be expected to fade over several months.

Auspitz sign refers to pinpoint bleeding upon removal of the scaly layer in plaque psoriasis. It is related to the dilated dermal capillaries involved in the histological pathogenesis of chronic psoriasis.

How is psoriasis classified?

Certain features of psoriasis can be categorised to help determine appropriate investigations and treatment pathways - overlap may occur. These include:

Types of psoriasis

Guttate psoriasis

Post-streptococcal acute guttate psoriasis

  • Widespread small plaques
  • Often resolves after several months

Guttate psoriasis

Small plaque psoriasis

  • Often late age of onset
  • Plaques <3 cm

Chronic plaque psoriasis

  • Persistent and treatment-resistant
  • Plaques >3 cm
  • Most often affects elbows, knees, and lower back
  • Ranges from mild to very extensive

Chronic plaque psoriasis

Unstable plaque psoriasis

  • The rapid extension of existing or new plaques
  • Koebner phenomenon: new plaques at sites of skin injury
  • Induced by infection, stress, drugs, or drug withdrawal

Flexural psoriasis (inverse psoriasis)

  • Affects body folds and genitals
  • Smooth, well-defined patches
  • Colonised by candida yeasts

Flexural psoriasis

Scalp psoriasis

  • Often the first or only site of psoriasis

Scalp psoriasis



Palmoplantar psoriasis

  • Affecting the palms and/or soles
  • Keratoderma
  • Painful fissuring

Palmoplantar psoriasis

Nail psoriasis

  • Pitting, onycholysis, yellowing, and ridging
  • Associated with inflammatory arthritis

Nail psoriasis

Erythrodermic psoriasis

  • Erythrodermic psoriasis is rare.
  • May or may not be preceded by another form of psoriasis
  • Acute and chronic forms
  • May result in systemic illness with temperature dysregulation, electrolyte imbalance, or cardiac failure

Erythrodermic psoriasis

There is some controversy as to whether generalised pustulosis and localised palmoplantar pustulosis are classified as being within the psoriasis spectrum.

How do clinical features vary in differing types of skin?

Plaque psoriasis is the most common type of psoriasis in all racial groups. Non-Caucasians tend to have more extensive skin involvement than Caucasians. Asian populations are reported to have the highest percentage of body surface area involvement.

In skin of colour, the plaques are typically thicker with a more pronounced silver scale and itch. The pinkness of early patches may be more difficult to appreciate.

Thick plaques may appear violet or dark in colour. Plaque psoriasis is more likely to result in postinflammatory hyperpigmentation or hypopigmentation in the skin of colour, which further impacts the quality of life even after disease clearance. 

Other types of psoriasis show variable rates in different skin types. Palmoplantar psoriasis is reported to be more common in the Indian population. Non-Caucasians are more likely to present with pustular and erythrodermic psoriasis than Caucasians, whereas flexural psoriasis is said to occur at a lower rate in skin of colour.

Plaque psoriasis in skin of colour

Factors that aggravate psoriasis

Health conditions associated with psoriasis

Patients with psoriasis are more likely than others to have associated health conditions such as are listed here.

Psoriasis and metabolic syndrome

Metabolic syndrome refers to the combination of obesity, hypertension, dyslipidaemia, and insulin resistance.

  • It is present in many patients with psoriasis, especially those with severe chronic plaque psoriasis.
  • The link between psoriasis, obesity, and type 2 diabetes mellitus is independent of age, sex, and smoking history. 
  • The link is thought to be due to genetic factors and the presence of chronic inflammation.
  • The interleukin (IL)-23/Th 17 axis drives both psoriatic skin inflammation and atherosclerosis; psoriasis is an independent risk factor for cardiovascular disease. 

Lifestyle modifications such as weight loss, lipid profile reduction, and tight control of glucose levels reduce the mortality from cardiovascular events in patients with psoriasis.

How is psoriasis diagnosed?

Psoriasis is diagnosed by its clinical features. If necessary, diagnosis is supported by typical skin biopsy findings.

Assessment of psoriasis

Medical assessment entails a careful history, examination, questioning about the effect of psoriasis on daily life, and evaluation of comorbid factors.

Validated tools used to evaluate psoriasis include:

  • Psoriasis Area and Severity Index (PASI)
  • Self-Administered Psoriasis Area and Severity Index (SAPASI)
  • Physicians/Patients Global Assessment (PGA)
  • Body Surface Area (BSA)
  • Psoriasis Log-based Area and Severity Index (PLASI)
  • Simplified Psoriasis Index
  • Dermatology Life Quality Index (DLQI)
  • SKINDEX-16

The severity of psoriasis is classified as mild in 60% of patients, moderate in 30% and severe in 10%.

Evaluation of comorbidities may include:

  • Psoriatic Arthritis Screening Evaluation (PASE) or Psoriasis Epidemiology Screening Tool (PEST)
  • Body mass index (BMI) and waist circumference
  • Blood pressure
  • Electrocardiogram (ECG)
  • Blood sugar/glucose level and glycated haemoglobin (HbA1c)
  • Lipid profile, liver function, and uric acid level.

Treatment of psoriasis

General advice

Patients with psoriasis should be well-informed about their skin condition and its treatment. Recommendations include:

  • Smoking cessation
  • Safe limits for alcohol consumption
  • Maintaining optimal weight.

Topical therapy

Mild psoriasis is generally treated with topical agents alone. The selected treatment depends on the body site and the extent and severity of psoriasis, and may include:


Most psoriasis centres offer phototherapy (light therapy) with ultraviolet (UV) radiation, often in combination with topical or systemic agents, including:

Systemic therapy

Moderate to severe psoriasis warrants treatment with a systemic agent and/or phototherapy. The most common treatments are:

Other medicines occasionally used for psoriasis include:

Systemic corticosteroids are best avoided due to the risk of severe withdrawal flare of psoriasis and adverse effects.

Biologic therapy

Biologic or biological therapy is reserved for severe psoriasis and psoriatic arthritis that have failed to respond to conventional systemic therapy. The use of biologics has increased with the development of novel therapies targeting key inflammatory pathways such as TNF-alpha and IL-17.

Biologics are costly and may result in side effects. They should be initiated by specialists familiar with their use.

TNF-alpha inhibitors:

Interleukin 17 (IL-17) inhibitors:

Interleukin 23 (IL-23) inhibitors:

Adalimumab, etanercept, and ustekinumab have been used to treat severe psoriasis in children

Newer agents:

  • Tapinarof 1% cream is an aryl hydrocarbon receptor agonist that downregulates TH2 cells, IL-17 activation, and disease severity. Tapinarof is undergoing Phase III trials for treatment in the paediatric population.
  • Small molecules: Deucravacitinib, brepocitanib, and ropsacitanib are tyrosine kinase 2 (TYK2) inhibitors (see Janus kinase inhibitors).



  • Chularojanamontri L, Griffiths CE, Chalmers RJ. The Simplified Psoriasis Index (SPI): a practical tool for assessing psoriasis. J Invest Dermatol. 2013;133(8):1956–62. doi: 10.1038/jid.2013.138. Journal
  • Fleming P. Tofacitinib: a new oral Janus kinase inhibitor for psoriasis. Br J Dermatol. 2019;180(1):13–14. doi: 10.1111/bjd.17323. Journal
  • Kamiya K, Kishimoto M, Sugai J, et al. Risk Factors for the Development of Psoriasis. Int J Mol Sci. 2019 Sep;20(18):4347. doi: 10.3390/ijms20184347. Journal
  • Keam SJ. Tapinarof Cream 1%: First Approval. Drugs. 2022;82(11):1221-1228. doi: 10.1007/s40265-022-01748-6. Erratum in: Drugs. 2022 Aug;: Erratum in: Drugs. 2022 Sep;82(13):1433. Journal
  • Mattei PL, Corey KC, Kimball AB. Psoriasis Area Severity Index (PASI) and the Dermatology Life Quality Index (DLQI): the correlation between disease severity and psychological burden in patients treated with biological therapies. J Eur Acad Dermatol Venereol. 2014 Mar;28(3):333-7. doi: 10.1111/jdv.12106. Article
  • Papp K, Gordon K, Thaçi D, et al. Phase 2 trial of selective tyrosine kinase 2 inhibition in psoriasis. N Engl J Med. 2018;379(14):1313–21. doi: 10.1056/NEJMoa1806382. Journal
  • Wu JJ, Kavanaugh A, Lebwohl MG, et al. Psoriasis and metabolic syndrome: implications for the management and treatment of psoriasis. J Eur Acad Dermatol Venereol. 2022 Jun;36(6):797-806. doi: 10.1111/jdv.18044. Article
  • Zhang L, Guo L, Wang L, Jiang X. The efficacy and safety of tofacitinib, peficitinib, solcitinib, baricitinib, abrocitinib and deucravacitinib in plaque psoriasis - A network meta-analysis. J Eur Acad Dermatol Venereol. 2022 Nov;36(11):1937-1946. doi: 10.1111/jdv.18263. Journal

Bibliography for psoriasis in skin of colour

  • Amico S, Barnetche T, Dequidt L, et al. Characteristics of postinflammatory hyper- and hypopigmentation in patients with psoriasis: a survey study. J Am Acad Dermatol. 2020;83(4):1188-91. doi: 10.1016/j.jaad.2020.02.025. Journal
  • Geng A, McDonald C. Psoriasis. In: Taylor SC, Kelly AP, Lim HW, Serrano AMA (eds). Taylor and Kelly's Dermatology for Skin of Color, 2nd edn. McGraw Hill, 2016: Chapter 24.
  • Kaufman BP, Alexis AF. Psoriasis in skin of color: insights into the epidemiology, clinical presentation, genetics, quality-of-life impact, and treatment of psoriasis in non-white racial/ethnic groups. Am J Clin Dermatol. 2018;19(3):405-423. Erratum in: Am J Clin Dermatol. 2018 Jun;19(3):425. doi:10.1007/s40257-017-0332-7. Article
  • Yan D, Afifi L, Jeon C, et al. A cross-sectional study of the distribution of psoriasis subtypes in different ethno-racial groups. Dermatol Online J. 2018;24(7):13030/qt5z21q4k2. Journal

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