Psoriasis

Psoriasis is an immune-mediated condition with a strong genetic component; the skin turns over far too fast. It is associated with psoriatic arthritis, metabolic syndrome, and cardiovascular risk, so it is not purely a skin problem.

Sunlight works, which is the observation that led to topical vitamin D analogues. Ultraviolet light, particularly narrow-band UVB in a clinical setting, is an effective treatment. Uncontrolled sunburn is not, and the balance between benefit and skin-cancer risk is why phototherapy is done in a clinic with a defined dose.

Topical treatments with evidence. Calcipotriol (a vitamin D analogue) is standard and derived directly from the sunlight observation. Topical corticosteroids, tar preparations (crude coal tar is effective and unpleasant), dithranol, and salicylic acid for scale. Aloe vera has a small trial showing improvement in psoriasis plaques; modest.

Systemic treatments for moderate to severe disease — methotrexate, ciclosporin, acitretin, and the biologics, which are highly effective. This is a specialist area, and the systemic drugs require monitoring.

The herbal options. Small trials exist for various preparations; none is a treatment for moderate to severe psoriasis, and some — importantly — interact. St John's wort is photosensitising and interacts with ciclosporin and methotrexate, and must not be combined with them. Any systemic herb in someone on methotrexate or ciclosporin is a potential interaction and a potential liver or kidney problem.

Other things that matter. Alcohol worsens it. Smoking worsens it and is a risk factor for the associated cardiovascular disease. Stress is associated with flares. Obesity is associated with severity, and weight loss improves it. Topical treatments need to be used consistently — a person who treats for three days and stops will not see a result, and the disease takes 4-8 weeks to respond.

The red flag. Psoriasis with severe widespread redness and scaling covering the body (erythrodermic) or with pustules and fever (generalised pustular) is a medical emergency. Psoriasis with joint pain and swelling needs assessment for psoriatic arthritis, because joint damage is permanent.