These include the following.
1 Traumaaif the psoriasis is active, lesions can appear in skin damaged by scratches or surgical wounds (the Köbner phenomenon; Fig. 5.1).
2 Infectionatonsillitis caused byβ-haemolytic strep-tococci often triggers guttate psoriasis. AIDS often worsens it, or precipitates explosive forms.
3 Hormonalapsoriasis frequently improves in preg-nancy only to relapse postpartum. Hypocalcaemia secondary to hypoparathyroidism is a rare precipitat-ing cause.
4 Sunlightaimproves most psoriatics but 10% become worse.
5 Drugsaantimalarials,βblockers, IFN-αand lith-ium may worsen psoriasis. Psoriasis may ‘rebound’ after withdrawal of treatment with systemic steroids or potent topical steroids. The case against non-steroidal anti-inflammatory drugs (NSAIDS) remains unproven.
6 Cigarette smoking and alcoholathe effects of con-founding variables have been difficult to unravel in most epidemiological studies but there is growing evidence that both have an independent effect in pre-cipitating or maintaining psoriasis.
7 Emotionaemotional upsets seem to cause someexacerbations.