Triggers

Inherited factors are important in psoriasis, with estimated 5.5 and 2.5-fold increased risks in individuals with affected first- and second-degree relatives respectively.

Psoriasis can also be triggered by:

• Skin trauma, where it develops at the site of an injury (known as the Koebner phenomenon)
• Climate, with symptoms often worse during colder weather
• Infections
• Medicines, including antimalarial drugs, beta-blockers and NSAIDs.

The precise cause of psoriasis remains unclear, although genetic, environmental and immunological factors are likely to be involved.

At its simplest, psoriatic skin reflects changes in the keratinocyte life cycle. Normally, keratinocytes are produced and replaced approximately every 28 days, but in psoriasis this is shortened to around five days. This rapid turnover leads to a build-up of keratinocytes on the skin surface, appearing as silvery-white scale.

Psoriatic plaques also show increased vasculature (increased blood flow and blood vessel growth), reflecting the inflammatory component of the disease.