What Is Psoriasis?1

Psoriasis is a chronic, noncommunicable, painful, disfiguring, and disabling disease for which there is no cure.3  Worldwide, approximately 2% to 3% of the population have psoriasis.4,5  There is evidence suggesting the prevalence of psoriasis may be increasing.3

The majority of people with psoriasis have mild disease, whereas fewer people have cases that are considered moderate to severe. The most common form of psoriasis is plaque psoriasis.2 The various forms of psoriasis will be discussed later in this document.


Some key information about the epidemiology of psoriasis is listed in Table 1. 

Variations in psoriasis prevalence are influenced by patient age, geography, and ethnicity, likely due to genetic and environmental differences among populations. Furthermore, estimates of psoriasis prevalence or incidence vary among different studies due to differences in methodology, such as study definitions, design, and sampling techniques.3,6

Table 1. Key psoriasis epidemiology information.

Psoriasis Epidemiology

Equally prevalent in women and men4

Affects individuals of all ages and ethnic origins3

More common among adults than children6

Some studies indicate the average age of onset for psoriasis is 33 years, with about 75% of cases occurring before 46 years of age3

Other studies indicate onset of psoriasis occurs in 2 peaks: the first between 16 and 22 years of age and the second between 57 and 60 years of age3

Most common in populations of northern Europe and least common in populations of eastern Asia3

Prevalence in different countries varies between 0.09% and 11.4%3

In most developed countries, prevalence is between 1.5% and 5%3

Studies in some countries have shown its prevalence may have more than doubled in the last few decades3

Risk Factors

Risk factors that may trigger or exacerbate psoriasis appear in Table 2.

Table 2. Risk factors in the development of psoriasis.

Psoriasis Risk Factors

   Risk Factor


Skin trauma

- Psoriasis lesions may appear in skin damaged by scratches or surgical wounds (Koebner phenomenon)1


- Toxins produced by certain bacteria can promote T-cell proliferation1
- Acquired immunodeficiency syndrome (AIDS) may precipitate certain forms of psoriasis1
- Flare-up can occur following strep throat, an earache, bronchitis, tonsillitis, or a respiratory infection1,7
Hormones - Psoriasis has been shown to improve during pregnancy and relapse after delivery1
Sunlight - Exposure to sunlight tends to improve psoriasis but may worsen psoriasis in some patients1
 Drugs - Administration of certain medications can worsen psoriasis1
- Psoriasis may return (rebound) following withdrawal of treatment with certain drugs1
- Psoriasis is more common in smokers and former smokers1
Emotional stress
- Psoriasis may be exacerbated during periods of emotional stress1
- Individuals with first- and second-degree relatives with psoriasis have a greater incidence of psoriasis than the general population8
- A child with 1 parent with psoriasis has about a 10% chance of developing the disease—50% if both parents have psoriasis4; some studies indicate there is a higher incidence when the father, rather than the mother, has psoriasis9
- Siblings of individuals with psoriasis carry a 4- to 6-fold risk of developing psoriasis compared to the general population10
- Rates among “identical” twins (35%-72%) are up to 3 times higher than among “fraternal” twins (12%-30%)8,9,11-14
- Overall, the heritability of psoriasis is estimated to be between 60% and 90%9,12,13- Patients with early-onset psoriasis tend to have a positive family history and more severe disease, whereas those with later onset tend to lack a family history of psoriasis and have less severe disease8,12
  1. Weller R, Hunter J, Savin J, et al. Psoriasis. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.; 2008:54-70.
  2. The psoriasis and psoriatic arthritis pocket guide. Treatment algorithms and management options, 4th edition. National Psoriasis Foundation. 2017:1-130. Available at: https://www.psoriasis.org/sites/default/files/npf_pocketguide_2017.pdf. Accessed February 28, 2018.
  3. World Health Organization. Global report on psoriasis. 2016. Available at: http://apps.who.int/iris/bitstream/10665/204417/1/9789241565189_eng.pdf. Accessed February 25, 2018.
  4. About Psoriasis. National Psoriasis Foundation. Available at: https://www.psoriasis.org/about-psoriasis. Accessed February 15, 2018.
  5. Griffiths CEM, van der Walt JM, Ashcroft DM, et al. The global state of psoriasis disease epidemiology: a workshop report. B J Dermatol. 2017;177(1):e4-e7.
  6. Parisi R, Symmons DPM, Griffiths CEM, et al. Global epidemiology of psoriasis: a systematic review of incidence and prevalence. J Invest Dermatol. 2013;133:377-385.
  7. Causes and triggers. National Psoriasis Foundation. Available at: https://www.psoriasis.org/about-psoriasis/causes. Accessed May 2, 2018.
  8. Boehncke WH. Etiology and pathogenesis of psoriasis. Rheum Dis Clin N Am. 2015;41: 665-675.
  9. Rahman P, Elder JT. Genetic epidemiology of psoriasis and psoriatic arthritis. Ann Rheum Dis. 2005;64(Suppl II): ii37-ii39.
  10. Roberson EDO, Bowcock AM. Psoriasis geneitics; breaking the barrier. Trends Genet. 2010;26(9):415-423.
  11. Eder L, Chandran V, Gladman DD. What have we learned about genetic susceptibility in psoriasis? Rheumatology. 2015;27(1):91-98.
  12. Wuepper KD, Coulter SN, Haberman A. Psoriasis vulgaris: a genetic approach. J Invest Dermatol. 1990;95:2S-4S.
  13. Duffy DL, Spelman LS, Martin NG. Psoriasis in Australian twins. J Am Acad Dermatol. 1993;29:428-434.
  14. Brandrup F, Hauge M, Henningsen K, Eriksen B. Psoriasis in an unselected series of twins. Arch Dermatol. 1978;114:874-878.

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