Merck Manual

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Shinjita Das

, MD, Harvard Medical School

Reviewed/Revised Sep 2023
Topic Resources

Psoriasis is an inflammatory disease that manifests most commonly as well-circumscribed, erythematous papules and plaques covered with silvery scales. Multiple factors contribute, including genetics. Common triggers include trauma, infection, and certain medications. Symptoms are usually minimal, but mild to severe itching may occur. Cosmetic implications may be major. Some people also develop psoriatic arthritis. Diagnosis is based on appearance and distribution of lesions. Treatment can include topical treatments (eg, corticosteroids, vitamin D3 analogs, calcineurin inhibitors, tazarotene, roflumilast, tapinarof, emollients, salicylic acid, coal tar, anthralin), phototherapy, and, when severe, systemic medications (eg, methotrexate, oral retinoids, cyclosporine, other immunosuppressants [biologics or small molecules]).

Psoriasis is hyperproliferation of epidermal keratinocytes combined with inflammation of the epidermis and dermis.

Estimates of the prevalence of psoriasis vary widely across different populations, and it is likely that psoriasis is underreported among people with dark skin compared with people with light skin (1 References Psoriasis is an inflammatory disease that manifests most commonly as well-circumscribed, erythematous papules and plaques covered with silvery scales. Multiple factors contribute, including... read more References ). One study reported rates ranging from 0 to 1.4% in children and 0.5 to 11.4% in adults (2 References Psoriasis is an inflammatory disease that manifests most commonly as well-circumscribed, erythematous papules and plaques covered with silvery scales. Multiple factors contribute, including... read more References ). Peak onset is roughly bimodal, most often at ages 16 to 22 and at ages 57 to 60, but the disorder can occur at any age.


  • 1. 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 19(3):405-423, 2018. doi: 10.1007/s40257-017-0332-7

  • 2. Michalek IM, Loring B, John SM: A systematic review of worldwide epidemiology of psoriasis. J Eur Acad Dermatol Venereol 31(2):205–212, 2017. doi: 10.1111/jdv.13854

Etiology of Psoriasis

The cause of psoriasis is unclear but involves immune stimulation of epidermal keratinocytes; T cells seem to play a central role. Family history is common, and certain genes and human leukocyte antigens (Cw6, B13, B17) are associated with psoriasis. Genomewide linkage analysis has identified numerous psoriasis susceptibility loci; the PSORS1 locus on chromosome 6p21 plays the greatest role in determining a patient's susceptibility of developing psoriasis. An environmental trigger is thought to evoke an inflammatory response and subsequent hyperproliferation of keratinocytes (1 Etiology reference Psoriasis is an inflammatory disease that manifests most commonly as well-circumscribed, erythematous papules and plaques covered with silvery scales. Multiple factors contribute, including... read more Etiology reference ).

Well-identified triggers include

  • Injury (Koebner phenomenon)

  • Sunburn

  • HIV infection

  • Beta-hemolytic streptococcal infection (leading to guttate psoriasis)

  • Medications (especially beta-blockers, chloroquine, lithium, angiotensin-converting enzyme inhibitors, indomethacin, terbinafine, interferon-alfa, immune checkpoint inhibitors, and tumor necrosis factor inhibitors)

  • Emotional stress

  • Alcohol consumption

  • Tobacco smoking

  • Obesity

Etiology reference

  • 1. Zhou X, Chen Y, Cui L, et al: Advances in the pathogenesis of psoriasis: From keratinocyte perspective. Cell Death Dis 13(1):81, 2022. doi: 10.1038/s41419-022-04523-3

Symptoms and Signs of Psoriasis

Lesions are either asymptomatic or pruritic and are most often localized on the scalp, extensor surfaces of the elbows and knees, sacrum, buttocks (commonly the gluteal cleft), and genitals. The nails, eyebrows, axillae, umbilicus, and perianal region may also be affected.

Plaques may look violaceous in patients with dark skin and pink or red in patients with light skin, but key features such as scaling and distribution (eg, on extensor elbows, trunk, legs, and periumbilical area) are consistent across all skin tones.

The disease can be widespread, involving confluent areas of skin extending between these regions.

Lesions differ in appearance depending on type.

Manifestations of Psoriasis

Among the various psoriasis subtypes (see table ), plaque psoriasis (psoriasis vulgaris or chronic plaque psoriasis) accounts for about 90%; lesions are discrete, erythematous papules or plaques covered with thick, silvery, shiny scales. Lesions appear gradually and remit and recur spontaneously or with the appearance and resolution of triggers.

Psoriasis is rarely life-threatening but can affect a patient’s self-image. Besides the patient's appearance, the sheer amount of time required to treat extensive skin or scalp lesions and to maintain clothing and bedding may adversely affect quality of life.


Diagnosis of Psoriasis

  • Clinical evaluation

  • Rarely biopsy

Diagnosis of psoriasis is most often by clinical appearance and distribution of lesions.

Differential diagnosis includes

Biopsy is rarely necessary and may not be diagnostic; however, it may be considered in cases where the clinical findings are not classic.

Disease is graded as mild, moderate, or severe based on the body surface area affected and how the lesions affect the patient's quality of life. To be considered mild, usually < 10% of the skin surface should be involved. There are many more complex scoring systems for disease severity (eg, the Psoriasis Area and Severity Index), but these systems are useful mainly in research protocols.

Treatment of Psoriasis

  • Topical treatments

  • Ultraviolet (UV) light therapy

  • Systemic therapies

Treatment options are extensive and range from topical treatments (eg, corticosteroids, vitamin D3 analogs, calcineurin inhibitors, tazarotene, roflumilast, tapinarof, emollients, salicylic acid, coal tar, anthralin) to UV light therapy to systemic treatments (eg, methotrexate, oral retinoids, cyclosporine, biologics, small molecules).

Topical treatments

Corticosteroids are usually used topically but may be injected into small or recalcitrant lesions. (CAUTION: Systemic corticosteroids may precipitate exacerbations or development of pustular psoriasis and should not be used to treat psoriasis.) Topical corticosteroids are used twice daily. Corticosteroids are most effective when used overnight under occlusive polyethylene coverings or incorporated into tape; a corticosteroid cream is applied without occlusion during the day. Corticosteroid potency Anti-inflammatory agents Topical dermatologic treatments are grouped according to their therapeutic functions and include Cleansing agents Moisturizing agents (emollients, skin hydrators, and softeners) Drying agents... read more is selected according to the extent of involvement.

As lesions abate, the corticosteroid should be applied less frequently or at a lower potency to minimize local atrophy, striae formation, and telangiectases. Ideally, after about 2 to 3 weeks, an emollient, vitamin D3 analog, or calcineurin inhibitor should be substituted for the corticosteroid for 1 to 2 weeks (as a rest period); this substitution limits corticosteroid dosage, reduces risk of topical corticosteroid adverse effects (eg, skin atrophy, telangiectasias, easy bruising, striae), and prevents tachyphylaxis (diminishing response to an agent after successive dosing). Topical corticosteroid use can be expensive because large quantities (about 1 oz or 30 g) are needed for each application when a large body surface area is affected. Topical corticosteroids applied for long duration to large areas of the body may cause systemic effects and exacerbate psoriasis. For small, thick, localized, or recalcitrant lesions, high-potency corticosteroids are used with an occlusive dressing or flurandrenolide tape; these dressings are left on overnight and changed in the morning. Relapse after topical corticosteroid therapy is stopped is often faster than with other agents.

Vitamin D3 analogs (eg, calcipotriol [calcipotriene], calcitriol) are topical medications that induce normal keratinocyte proliferation and differentiation; they can be used alone or in combination with topical corticosteroids. Some clinicians have patients apply calcipotriol on weekdays and corticosteroids on weekends.

Calcineurin inhibitors (eg, tacrolimus, pimecrolimus) are available in topical form and are generally well-tolerated. They are not as effective as corticosteroids but may avoid the complications of corticosteroids when treating facial and intertriginous psoriasis. It is not clear whether they increase the risk of lymphoma and skin cancer.

Tazarotene is a topical retinoid. It is less effective than corticosteroids as monotherapy but is a useful adjunct because of its keratolytic effect. It is typically used on thicker psoriasis plaques that may appear on the trunk and extremities but also may be used on the face.

Roflumilast is a topical phosphodiesterase-4 (PDE-4) inhibitor. It is particularly useful as a corticosteroid-sparing treatment for facial and intertriginous areas (eg, buttocks, groin, axillae).

Tapinarof is a topical aryl hydrocarbon receptor (AhR) agonist. It is also useful as a corticosteroid-sparing therapy on facial and intertriginous areas.

Other adjunctive topical treatments include emollients, salicylic acid, coal tar, and anthralin:

  • Emollients include emollient creams, ointments, petrolatum, paraffin, and even hydrogenated vegetable (cooking) oils. They reduce scaling and are most effective when applied twice daily and immediately after bathing. Lesions may appear redder as scaling decreases or becomes more transparent. Emollients are safe and should generally be used as and adjunct for mild to moderate plaque psoriasis.

  • Salicylic acid is a keratolytic that softens scales, facilitates their removal, and increases absorption of other topical agents. It is especially useful as a component of scalp treatments; scalp scale can be quite thick.

  • Coal tar preparations are anti-inflammatory and decrease keratinocyte hyperproliferation via an unknown mechanism. Ointments or solutions are typically applied at night and washed off in the morning. Coal tar products can be used in combination with topical corticosteroids or with exposure to natural or artificial broad-band UVB light (280 to 320 nm) in slowly increasing increments (Goeckerman regimen). Shampoos should be left in for 5 to 10 minutes and then rinsed out.

  • Anthralin is a topical antiproliferative, anti-inflammatory agent. Its mechanism of action is unknown. Effective dose is 0.1% cream or ointment increased to 1% as tolerated. Anthralin may be irritating and should be used with caution in intertriginous areas; it also stains. Irritation and staining can be avoided by washing off the anthralin 20 to 30 minutes after application. Using a liposome-encapsulated preparation may also avoid some disadvantages of anthralin.

Given the availability and convenience of other agents, coal tar and anthralin are being used less frequently.


UV light therapy is typically used in patients with extensive psoriasis; however, its use is declining because of the availability of various effective systemic therapies. The mechanism of action is unknown, although UVB light reduces DNA synthesis and can induce mild systemic immunosuppression. In psoralen plus ultraviolet A (PUVA), oral methoxypsoralen, a photosensitizer, is followed by exposure to long-wave UVA light (330 to 360 nm). PUVA has an antiproliferative effect and also helps to normalize keratinocyte differentiation. Doses of light are started low and increased as tolerated. Severe burns can result if the dose of medication or UVA is too high.

Although the treatment is less messy than topical treatments and may produce remissions lasting several months, repeated treatments may increase the incidence of UV-induced skin cancer and melanoma. Less UV light is required when used with oral retinoids (the so-called re-PUVA regimen). Narrowband UVB light (311 to 312 nm), which is used without psoralens, is similar in effectiveness to PUVA. Excimer laser therapy is a type of phototherapy using a 308-nm laser directed at focal psoriatic plaques.

Systemic therapies

Methotrexate taken orally is an effective treatment for severe disabling psoriasis, especially severe psoriatic arthritis or widespread erythrodermic or pustular psoriasis unresponsive to topical agents or UV light therapy (narrowband UVB) or PUVA. Methotrexate seems to interfere with the rapid proliferation of epidermal cells. Hematologic, renal, and hepatic function should be monitored. Dosage regimens vary, so only physicians experienced in its use for psoriasis should undertake methotrexate therapy.

Cyclosporine can be used for severe psoriasis. It should be limited to courses of several months (rarely, up to 1 year) and alternated with other therapies. Its effect on the kidneys and potential long-term effects on the immune system preclude more liberal use.

Mycophenolate mofetil can be an alternative option for patients who do not respond to methotrexate or cyclosporine or those who develop toxicity from the above medications.

Systemic retinoids (eg, acitretin, isotretinoin) may be effective for severe and recalcitrant cases of psoriasis vulgaris, pustular psoriasis (in which isotretinoin may be preferred), and hyperkeratotic palmoplantar psoriasis. Because of the teratogenic potential and long-term retention of acitretin in the body, women who use it must not be pregnant and should be warned against becoming pregnant for at least 3 years after treatment ends. Pregnancy restrictions also apply to isotretinoin, but the agent is not retained in the body beyond 1 month. Long-term treatment may cause diffuse idiopathic skeletal hyperostosis Diagnosis Ankylosing spondylitis is the prototypical spondyloarthropathy and a systemic disorder characterized by inflammation of the axial skeleton, large peripheral joints, and digits; nocturnal back... read more Diagnosis (DISH).

  • TNF inhibitors: Etanercept, adalimumab, infliximab, and certolizumab pegol (does not cross the placenta)

  • Interleukin (IL)-23 inhibitors: Tildrakizumab, risankizumab, guselkumab, and ustekinumab (targets both IL-12 and IL-23)

  • IL-17 inhibitors: Secukinumab, ixekizumab, and brodalumab

Apremilast, a PDE-4 inhibitor, is an oral small-molecule medication for plaque psoriasis; however, postmarketing data suggest it is less effective than biologics (3 Treatment references Psoriasis is an inflammatory disease that manifests most commonly as well-circumscribed, erythematous papules and plaques covered with silvery scales. Multiple factors contribute, including... read more Treatment references ).

Spesolimab is an IL-36 inhibitor that may be used to treat generalized pustular psoriasis.

Biosimilar medications are being developed and used for various therapeutic monoclonal antibodies as their patents expire (7 Treatment references Psoriasis is an inflammatory disease that manifests most commonly as well-circumscribed, erythematous papules and plaques covered with silvery scales. Multiple factors contribute, including... read more Treatment references ). These medications have very similar efficacies and toxicities to reference products; slight differences in components are not clinically meaningful.

Other immunosuppressants (eg, hydroxyurea, 6-thioguanine) have narrow safety margins and are reserved for severe, recalcitrant psoriasis. Efalizumab is no longer available in the United States or Canada because of increased risk of progressive multifocal leukoencephalopathy Progressive Multifocal Leukoencephalopathy (PML) Progressive multifocal leukoencephalopathy (PML) is caused by reactivation of the JC virus. The disease usually occurs in patients with impaired cell-mediated immunity, particularly patients... read more Progressive Multifocal Leukoencephalopathy (PML) .

Choice of therapy

Choice of specific agents and combinations requires close cooperation with the patient, always keeping in mind the untoward effects of the treatments. There is no single ideal combination or sequence of agents, but treatment should be kept as simple as possible. Monotherapy is preferred, but combination therapy is the norm. First-line treatment for psoriasis includes topical corticosteroids and topical vitamin D3 analogs (either as monotherapy or in combination).

Rotational therapy refers to the substitution of one therapy for another after 1 to 2 years to reduce the adverse effects caused by chronic use and to circumvent disease resistance. Sequential therapy refers to initial use of potent agents (eg, cyclosporine) to quickly gain control followed by use of agents with a better safety profile. Immunosuppressants achieve clearance or near clearance of lesions more often than methotrexate or narrowband UVB.

Mild plaque psoriasis can be treated with emollients, keratolytics, tar, topical corticosteroids, corticosteroid-sparing topical agents (eg, calcineurin inhibitors, PDE-4 inhibitors, tapinarof), vitamin D3 analogs, or anthralin alone or in combination. Moderate exposure to sunlight is beneficial, but sunburn can induce exacerbations.

Moderate to severe plaque psoriasis should be treated with topical agents and either phototherapy or systemic agents. Immunosuppressants are used for moderate to severe disease unresponsive to other agents.

Scalp plaques are notoriously difficult to treat because they resist systemic therapy, and because hair blocks application of topical agents and scale removal and shields skin from UV light. A suspension of 10% salicylic acid in mineral oil may be rubbed into the scalp at bedtime manually or with a toothbrush, covered with a shower cap (to enhance penetration and avoid messiness), and washed out the next morning with a tar (or other) shampoo. More cosmetically acceptable corticosteroid solutions can be applied to the scalp during the day. These treatments are continued until the desired clinical response is achieved.

Resistant skin or scalp patches may respond to local superficial intralesional injection of triamcinolone acetonide suspension diluted with saline to 2.5 or 5 mg/mL, depending on the size and severity of the lesion. Injections may cause local skin atrophy, which is usually reversible.

Severe cases of scalp psoriasis may need to be treated with systemic immunosuppressants (eg, biologics, small molecules).

Special treatment needs for subtypes of psoriasis Subtypes of Psoriasis Subtypes of Psoriasis are described above.

(See also the American Academy of Dermatology's clinical guideline for psoriasis.)

Treatment references

  • 1. Sbidian E, Chaimani A, Garcia-Doval I, et al: Systemic pharmacological treatments for chronic plaque psoriasis: A network meta-analysis. Cochrane Database Syst Rev 12(12):CD011535, 2017. doi: 10.1002/14651858.CD011535.pub2

  • 2. Armstrong AW, Read C: Pathophysiology, clinical presentation, and treatment of psoriasis: A review. JAMA 323(19):1945–1960, 2020. doi: 10.1001/jama.2020.4006

  • 3. Armstrong AW, Puig L, Joshi A, et al: Comparison of Biologics and Oral Treatments for Plaque Psoriasis: A Meta-analysis. JAMA Dermatol 156(3):258–269, 2020. doi: 10.1001/jamadermatol.2019.4029

  • 4. Armstrong AW, Gooderham M, Warren RB, et al: Deucravacitinib versus placebo and apremilast in moderate to severe plaque psoriasis: Efficacy and safety results from the 52-week, randomized, double-blinded, placebo-controlled phase 3 POETYK PSO-1 trial. J Am Acad Dermatol 88(1):29–39, 2023. doi: 10.1016/j.jaad.2022.07.002

  • 5. Strober B, Thaçi D, Sofen H, et al: Deucravacitinib versus placebo and apremilast in moderate to severe plaque psoriasis: Efficacy and safety results from the 52-week, randomized, double-blinded, phase 3 Program fOr Evaluation of TYK2 inhibitor psoriasis second trial. J Am Acad Dermatol 88(1):40–51, 2023. doi: 10.1016/j.jaad.2022.08.061

  • 6. Bachelez H, van de Kerkhof PC, Strohal R, et al: Tofacitinib versus etanercept or placebo in moderate-to-severe chronic plaque psoriasis: A phase 3 randomised non-inferiority trial. Lancet 386(9993):552-561, 2015. doi: 10.1016/S0140-6736(14)62113-9

  • 7. Ruda RC, Kelly KA, Feldman SR: Real-world outcomes following switching from anti-TNF reference products to biosimilars for the treatment of psoriasis. J Dermatolog Treat 34(1):2140569, 2023. doi: 10.1080/09546634.2022.2140569

Key Points

  • Psoriasis is a common inflammatory disorder affecting the skin that has a genetic component and several triggers (eg, trauma, infection, certain medications).

  • The most common skin findings are usually well-circumscribed, erythematous papules and plaques covered with silvery scales in plaque psoriasis, but lesions differ between the other less common subtypes of psoriasis.

  • Psoriatic arthritis develops in 5 to 30% of patients and can cause joint destruction and disability.

  • Diagnose based on the appearance and distribution of lesions.

  • Consider topical treatments (eg, emollients, salicylic acid, coal tar preparations, anthralin, corticosteroids, vitamin D3 analogs, calcineurin inhibitors, PDE-4 inhibitors, tapinarof, tazarotene), particularly for mild disease.

  • For moderate to severe psoriasis, consider systemic treatments such as retinoids, methotrexate, cyclosporine, biologics (eg, TNF inhibitors), and small molecules (eg, deucravacitinib).

  • Ultraviolet (UV) light therapy may be an alternative for patients who resist systemic immunosuppression.

More Information

The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

Drugs Mentioned In This Article

Drug Name Select Trade
Otrexup, Rasuvo, RediTrex, Rheumatrex, Trexall, Xatmep
Cequa, Gengraf , Neoral, Restasis, Sandimmune, SangCya, Verkazia
Eskalith, Eskalith CR, Lithobid
Indocin, Indocin SR, TIVORBEX
Desenex Max, Lamisil, Lamisil AT, Lamisil AT Athletes Foot, Lamisil AT Jock Itch, Terbinex
ARAZLO, Avage, Fabior, TAZORAC
Daliresp, ZORYVE
Akurza , Aliclen, Bensal HP, Clear Away, Clear Away Liquid, Clear Away One Step, Clear Away Plantar, Clearasil Rapid Rescue Deep Treatment, Compound W, Compound W Total Care Wart & Skin, Corn/Callus Remover, Curad Mediplast, DermacinRx Atrix, DermacinRx Salicate, Dermarest Psoriasis Moisturizer, Dermarest Psoriasis Overnight Treatment, Dermarest Psoriasis Scalp Treatment, Dermarest Psoriasis Shampoo plus Conditioner, Dermarest Psoriasis Skin Treatment, Dr. Scholl's Callus Removers, Dr. Scholl's Corn Removers, Dr. Scholl's Extra Thick Callus Remover, Dr. Scholl's One Step Callus Remover, Dr. Scholl's One Step Corn Removers, Dr. Scholl's Ultra, Dr.Scholl's Dual Action FREEZE AWAY, Dr.Scholl's Duragel, DuoFilm Wart Remover, Freezone, Gold Bond Psoriasis Relief, Gordofilm , Hydrisalic, Ionil, Ionil Plus, Keralyt, Keralyt 5, Keralyt Scalp Complete, MOSCO Callus & Corn Remover, MOSCO One Step Corn Remover, Neutrogena Acne Wash, Neutrogena T/Sal Scalp, Occlusal-HP, P&S, RE SA , SalAC, Salactic Film , Salacyn, Salex, Salimez, Salimez Forte, Salisol , Salisol Forte , Salitech, Salitech Forte, Salitop , Salkera, Salvax, Scalpicin 2 in 1 Anti-Dandruff, Selsun Blue, Thera-Sal , Trans-Ver-Sal, UltraSal-ER, VIRASAL, Wart-Off, XALIX
Balnetar, Cutar, Doak Tar, Fototar, Ionil T, Ionil T Plus, Neutrogena T/Gel Shampoo, Oxipor VHC Psoriasis, Pentrax, Psorigel, Reme-T, Scytera , Sebutone, Tarsum, Tera-Gel, Therapeutic Shampoo, Theraplex T, X-Seb T, Zetar
Dritho-Creme HP , Dritho-Scalp, Micanol, Psoriatec, ZITHRANOL, ZITHRANOL-RR
Cordran, Cordran SP, Cordran Tape, Nolix
Calcitrene , Calsodore, Dovonex, Dovonex Scalp, Sorilux, Trionex
Calcijex, Rocaltrol, Vectical
CellCept, Myfortic
Absorica, Absorica LD, Accutane, Amnesteem , Claravis , MYORISAN, Sotret, ZENATANE
Xeljanz, Xeljanz Oral, Xeljanz XR
DROXIA, HYDREA, Mylocel, Siklos
Fleet, Kondremul, Liqui-Doss, Muri-Lube
Aristocort, Aristocort A, Aristocort Forte, Aristocort HP, Aristo-Pak, Aristospan, Azmacort, Children's Nasacort Allergy 24HR Nasal Spray, Cinalog, Cinolar, Flutex, Hexatrione, Kenalog, Kenalog in Orabase, Kenalog-10, Kenalog-40, Kenalog-80, Nasacort, Nasacort AQ, Oralone, SP Rx 228 , Tac-3 , Triacet , Triamonide , Trianex , Triderm , Triesence, XIPERE, Zilretta
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