The aetiology of psoriasis is multifactorial:
- genetic:
- about 30% of patients having one first degree relative with psoriasis themselves develop the disease; for patients having two infected first degree relatives, the figure is about 60%
- there are strong HLA associations (HLA CW6)
- note - environmental factors are important - monozygotic twin studies show a concordance rate of only 40 to 65%
- infection:
- Streptococcal pharyngitis (1) - may cause guttate psoriasis, usually in children and young adults, and within 10-14 days; this pattern is associated with HLA-Cw6 in about 75% of cases
- AIDS/HIV (1)
- skin lesions identical to psoriasis may arise in patients with Reiter's syndrome
- stress, e.g. moving house; examinations
- trauma:
- Koebner phenomenon - skin disease occurring in scars or sites of trauma - well recognised in psoriasis (1)
- drugs:
- alcohol
- beta blockers
- non-steroidal anti-inflammatory drugs
- antimalarials, e.g. chloroquine
- mepacrine
- Lithium (1)
- Some treatment methods of psoriasis (e.g., anthralin and phototherapy) - if treated with high initial doses (1)
- Smoking (2). Alcohol is often cited as a potential risk factor but the evidence for this is not definitive (2)
Reference:
1. Schon MP, Boehncke WH. Psoriasis. N Engl J Med. 2005 May 5;352(18):1899-912.
2. Wei J et al. Alcohol consumption and smoking in relation to psoriasis: a Mendelian randomization study. Br J Dermatol. 2022 Nov;187(5):684-691