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Research Updates

Joel M. Gelfand, MD

Comorbidities in Psoriasis: Part One

Joel Gelfand

Tuesday, October 02, 2007

Psoriasis is a common chronic inflammatory disease of the skin that has been associated with a variety of comorbidities. More recent work has focused on how comorbid diseases and exposures can be risk factors for the development of psoriasis, as well as how chronic psoriasis can be a risk factor for the development of other diseases that share a common immune pathophysiology.

A risk factor is an exposure or characteristic that increases an individual's chance for developing a certain outcome, and by definition, the association is not explained by confounding (e.g. third factors that explain the association) or bias (e.g. systematic error in how patients are selected or information is collected). A risk factor may suggest a causal relationship based on strength of study design (randomized controlled trial is the gold standard), temporal relationship, strength of the association, consistency of studies, and biological plausibility.

In this review, I will summarize some of the major comorbidities associated with psoriasis, highlighting recent studies that evaluate risk factors for onset of psoriasis or exacerbation of psoriasis, and studies that evaluate psoriasis as a risk factor for developing diseases that share a similar immune pathophysiology.

This commentary will address infection, body mass index (BMI), and smoking and alcohol. In Part Two, I will address cancer, cardiovascular and metabolic disease, psychiatric disease, and psoriatic arthritis.


At this time, large-scale, analytical, epidemiological studies of the association between onset of plaque psoriasis and infection, as well as the risk of infections in patients with chronic psoriasis, are lacking.1 It is, however, well accepted that there is an association between the onset and flaring of guttate psoriasis and streptococcal pharyngitis2-4, with a plausible biological mechanism of sequence similarities between streptococcal M peptides and human keratins5. There is also an association between HIV infection and severe psoriasis3,6 as it is thought that HIV may act as a superantigen in the activation of T cells.6

Body Mass Index (BMI)

Several studies have implicated an association between psoriasis and obesity. For example, a large population-based cross-sectional study showed an increased odds ratio for obesity in patients with mild (OR, 1.27; 95% CI 1.24-1.31) and severe psoriasis (OR, 1.79; 95% CI 1.55-2.05).7 The directionality of the relationship of obesity and psoriasis was addressed by a case-control study of recent-onset psoriasis, in which obesity was found to be an independent risk factor for the development of psoriasis.8 In another study, obesity was associated with psoriasis but was not found to be a risk factor for developing it, suggesting that psoriasis patients may become obese over time.9


Smoking was established as a possible risk factor for chronic plaque psoriasis based on a case-control study that found an overall increased risk for the development of psoriasis in current (OR 1.7; 95%CI 1.1-3.0) and former (OR 1.9; 95%CI 1.3-2.7) smokers.8 A plausible biologic mechanism for this association exists in that nicotine has been shown to activate dendritic and T cells, as well as increase the secretion of pro-inflammatory Th1 cytokines and accelerate keratinocyte differentiation.10-14 Studies from numerous countries (Italy, United Kingdom, China, Finland, and United States) have found an increased prevalence of smoking in patients with psoriasis, with odds ratios varying from 1.7 to 3.7.7,9,15-18 In a hospital-based, cross-sectional study, smoking more than 20 cigarettes daily (vs. less than 10) was associated with a greater-than-twofold increased odds of clinically more severe psoriasis after controlling for several potential confounders.19 A strong link between smoking and palmoplantar pustular psoriasis has also been described.8,20


Several case-control studies have evaluated alcohol intake as a risk factor for psoriasis and have yielded inconsistent findings.17,21-23 Although alcohol consumption may not be a risk factor in the onset of psoriasis, several prevalence studies have shown an association between alcohol consumption and psoriasis, with positive findings being more consistently demonstrated in male psoriasis patients.15,24-29 Additional studies suggest that alcohol use may be associated with more severe skin disease and treatment non-compliance.17,30

Part Two

Read about cancer, cardiovascular and metabolic disease, psychiatric disease, and psoriatic arthritis here.


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  4. Whyte HJ, Baughman RD. Acute guttate psoriasis and streptococcal infection. Arch Dermatol. 1964;89:350-6.
  5. Gudmundsdottir AS, Sigmundsdottir H, Sigurgeirsson B, et al. Is an epitope on keratin 17 a major target for autoreactive T lymphocytes in psoriasis? Clin Exp Immunol. 1999;117:580-6.
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  21. Poikolainen K, Reunala T, Karvonen J, et al. Alcohol intake: a risk factor for psoriasis in young and middle aged men? BMJ. 1990;300:780-3.
  22. Naldi L, Parazzini F, Brevi A, et al. Family history, smoking habits, alcohol consumption and risk of psoriasis. Br J Dermatol. 1992;27:212-7.
  23. Duffy DL, Spelman LS, Martin NG. Psoriasis in Australian twins. J Am Acad Dermatol. 1993;29:428-34.
  24. Huriez C, Desmons F, Benoit M, et al. Liver biopsy in eczema and other dermatoses. Br J Dermatol. 1957;69:237-44.
  25. Behnam SM, Behnam SE, Koo JY. Alcohol as a risk factor for plaque-type psoriasis. Cutis. 2005;76:181-5.
  26. Chaput JC, Poynard T, Naveau S, et al. Psoriasis, alcohol, and liver disease. Br Med J (Clin Res Ed). 1985;291:25.
  27. Higgins EM, du Vivier AW. Cutaneous disease and alcohol misuse. Br Med Bull. 1994;50:85-98.
  28. Poikolainen K, Karvonen J, Pukkala E. Excess mortality related to alcohol and smoking among hospital-treated patients with psoriasis. Arch Dermatol. 1999;135:1490-3.
  29. Gupta MA, Schork NJ, Gupta AK, et al. Alcohol intake and treatment responsiveness of psoriasis: a prospective study. J Am Acad Dermatol. 1993;28:730-2.
  30. Zaghloul SS, Goodfield MJ. Objective assessment of compliance with psoriasis treatment. Arch Dermatol. 2004;140:408-14.