What does cold weather, moving house and bone fractures have in common you may wonder? Each is known to contribute to psoriasis.

Psoriasis is a multi-faceted disease and its origin and manifestation is an integration of hereditary factors, mind and body synchrony and environmental influences.

Environmental factors

Various events have been found to bring on psoriasis and psoriatic arthritis. These events represent only a fraction of the overall cause of psoriasis. Although they do not include our genetic disposition to the disease, these new discoveries of human psoriatic populations worldwide give us a chance to make changes to lessen our disease burden.

These environmental factors have been shown to be associated with skin psoriasis:

• streptococcal pharyngitis (with guttate psoriasis)
• stressful life events
• low humidity
• Human Immunodeficiency Virus (HIV) infection
• trauma (physical trauma may bring on Koebner response)
• smoking
• drugs (beta-blockers, lithium, anti-malarial, Interferon)
• cold weather
• diet
• obesity [1,2,3,4].

These environmental factors have demonstrated their link with psoriatic arthritis:

• associations with Rubella vaccination
• injury sufficient to require a medical consultation
• recurrent oral ulcers
• moving house
• fractured bone requiring hospital admission
• HIV infection [5,6].

Environmental examples out of Africa

Higher rates of incidence for psoriasis are constantly observed in eastern Africa than in western Africa. Cw6 is the strongest genetic component linked to psoriasis and psoriatic arthritis. The distribution of Cw6 is the same in the eastern and western Africa black population. Increased severity of psoriasis with low humidity is well known. In this example we can compare populations that share similar genetics however live in different climate zones. High humid rainy conditions of Nigeria (west Africa) and adjacent areas compared with the dry rainless climates of Kenya and Uganda (both east Africa) may contribute to the lower frequency of psoriasis on the humid west coast of Africa [1,2].

Environmental examples out of upper northern hemisphere

In the circumpolar population low frequency of diabetes, coronary artery disease (CAD) and psoriasis has been observed. For their food from Alaska through Canada and Greenland to Siberia people depend on land and marine animals, which include seal, walrus, whale, bear, caribou, musk ox, fish and birds. The traditional diet in this population is thus low in carbohydrate and high in protein and fat. It is believed that the high content of polyunsaturated fats in the Inuit diet contribute to the reduced prevalence of inflammatory diseases such as psoriasis and CAD [1,2]. The fat of arctic marine animals is the most unsaturated found in the animal kingdom, being particularly rich in essential fatty acids. Because of these observations fish oil as a supplementary therapy for psoriasis has been suggested.

Smoking

Smoking, psoriasis and psoriatic arthritis have an interesting relationship. Smoking is a risk factor for the development of psoriasis and there is a dose-response relationship [7].

Interestingly, the time to the development of psoriatic arthritis decreases with smoking prior to psoriasis onset. This means if someone smokes cigarettes before developing psoriasis, there is a shorter time before they may develop psoriatic arthritis.

On the other hand, the time to development of psoriatic arthritis increases with smoking after psoriasis onset. This means if cigarette smoking starts after the onset of psoriasis there is a longer time before the smoker may develop psoriatic arthritis [8]. In a 2009 study of smoking and psoriasis, it was shown that three minor genetic variants are associated with protection from psoriatic arthritis [9]. No association with psoriasis was seen when psoriatic arthritis cases were excluded. Smoking appeared to do away with this genetic protective effect [9]. It needs to be said that this study represents a small contribution to what stimulates psoriasis, and however interesting this gene variant acts, there is nothing ever good about cigarette smoking.

Conclusion

You may have happily noticed that coffee and wine are not mentioned as increasing the severity of psoriasis. However, before you fill your mug or glass, I bring you the sad news that this list is not comprehensive. There is an overwhelming amount of research data that supports healthy lifestyle, clean air, clean food and clean thought as a way to reduce and remove psoriasis.  This includes a good drop in moderation!

There have been major advances in understanding the incidence, distribution, and possible control of psoriasis as well as the genetics of psoriasis and psoriatic arthritis. A number of susceptibilities for the disease have been discovered and the pace of discovery has accelerated. Studies also have to be extended to different ethnicities and geographic regions to isolate their risk factors so that we can better understand the origin of psoriasis and the best and safest treatment.

References

[1] Raychaudhuri SP, Farber EM. The prevalence of psoriasis in the world. J Eur
Acad Dermatol Venereol 2001;15:16e7

[2] Farber EM, Nall L. Epidemiology: natural history and genetics. In: Roenigk Jr HH,
Maibach HI, editors. Psoriasis. New York: Dekker; 1998. p. 107 e57

[3] Gudjonsson JE, Thorarinsson AM, Sigurgeirsson B, Kristinsson KG,
Valdimarssonn H. Streptococcal throat infections and exacerbation of chronic
plaque psoriasis: a prospective study. Br J Dermatol 2003;149:530 e4.

[4] Raychaudhuri SP, Gross J. Psoriasis risk factors: role of lifestyle practices. Cutis
2000;66:348 e52.

 [5] Pattison E, Harrison BJ, Griffiths CE, Silman AJ, Bruce IN. Environmental risk
factors for the development of psoriatic arthritis: results from a case-control
study. Ann Rheum Dis 2008;67:672 e6.

[6] Reveille JD, Williams FM. Infection and musculoskeletal conditions: rheumatologic complications of HIV infection. Best Pract Res Clin Rheumatol
2006;20:1159 e79.

[7]Setty AR, Curhan G, Choi HK. Smoking and the risk of psoriasis in women:
Nurses’ Health Study II. Am J Med 2007;120:953 e9.

[8] Rakkhit T, Wong B, Nelson TS, Hansen CB, Papenfuss JS, Panko J, et al. Time to
development of psoriatic arthritis decreases with smoking prior to psoriasis
onset and increases with smoking after psoriasis onset. J Invest Dermatol
2007;127(Suppl. 1):S52.

[9] Duffin KC, Freeny IC, Schrodi SJ, Wong B, Feng BJ, Soltani-Arabshahi R, et al.
Association between IL13 polymorphisms and psoriatic arthritis is modified
by smoking. J Invest Dermatol 2009;129:2777 e83.