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Causes and Risk Factors

The precise cause of psoriasis is unknown. While there is a strong genetic component, psoriasis also has many environmental and lifestyle triggers including injury, sunburn, infection, obesity, certain medications, emotional stress, alcohol, and tobacco (Monteleone 2011; Traub 2007; Jariwala 2007; Cai 2012), which interact with the immune system, causing inflammation and rapid proliferation of skin cells (Siegel 2013; Armstrong 2014; NIH 2013; UMMC 2014a).


Psoriasis is a highly heritable disorder, with genetics believed to be an important contributor in up to 90% of cases, and a markedly increased risk in those with a first- or second-degree relative with the condition. The risk of developing psoriasis is 60% in those with two affected parents (Gupta 2014; Eder 2015; Usatine 2013; Hall 2015).

While psoriasis involves multiple genes, a variant gene called HLA-Cw6 appears to confer the greatest risk. This gene is part of a family of genes, referred to as the HLA complex, that is strongly associated with common autoimmune diseases including type 1 diabetes, celiac disease, and multiple sclerosis (Kaukinen 2002; Bahcetepe 2013; Gupta 2014; Delves 2014).

Streptococcal Infection

A streptococcal infection of the throat and tonsils often precedes guttate psoriasis, and streptococcal infections may also exacerbate other types of psoriasis (Armstrong 2014; NIH 2013; Mallbris 2009). The association between streptococcal infection and guttate psoriasis has been known for decades, and is quite strong (Telfer 1992; Leung 1995; Whyte 1964). In one study, psoriasis patients had approximately 10-fold higher frequency of strep throat than healthy controls (Gudjonsson 2003). Also, tonsillectomy has been shown to substantially reduce the severity of psoriasis (Thorleifsdottir 2012).

Table 2: Environmental and Lifestyle Risk Factors for Psoriasis

Risk Factors


Injury (Koebner phenomenon)

Response to skin trauma, including surgical scars, injection sites, abrasions, sunburn, allergic reactions, or other rashes

Infection (bacterial, viral)

Streptococcal infection in the upper respiratory tract is strongly associated with guttate psoriasis and may worsen plaque psoriasis; human immunodeficiency virus (HIV); EV-HPV, a strain of human papillomavirus (HPV)


Certain drugs can trigger an outbreak or worsen the condition, including beta-blockers, ACE inhibitors, lithium, chloroquine, and indomethacin; withdrawal of systemic steroids


Cold, dry air can be a trigger; some patients improve in spring


Stressful events or chronic stress can exacerbate psoriasis and contribute to flare-ups; stress reduction techniques may help control the condition


A review of studies involving nearly 135 000 psoriasis patients showed a positive association between body mass index and the severity of psoriasis

Tobacco smoking

Smokers have an increased risk of psoriasis; the risk of pustular psoriasis is 5.3 times greater

Alcohol abuse

Excessive alcohol consumption is associated with psoriasis

Poor sleep hygiene

Sleep deprivation and shift work appear to intensify psoriatic skin inflammation and increase the risk of developing psoriasis

(Fleming 2015; Adamzik 2013; Armstrong 2014; UMMC 2014a; Schalock 2014; Gudjonsson 2003; Majewski 2002; Majewski 2003; Boyd 1999; Ferri 2015; Usatine 2013; Hirotsu 2012; Li, Qureshi 2013)

Associated Diseases

Systemic inflammation increases risk for several other diseases among psoriasis patients (Ni 2014; Ryan 2015; Siegel 2013; Padhi 2013; Dowlatshahi 2013; McDonald 2012; Tobin 2011):