Determination of solar ultraviolet dose in the Dead Sea treatment of psoriasis.

Background: An increased risk of developing cancer of the skin is the only potentially serious (albeit unproven) long-term side effect of heliotherapy and it is therefore prudent to avoid unnecessary exposure to solar ultraviolet radiation. Traditional heliotherapy for psoriasis at the Dead Sea calls for a sun exposure of 5-6 hours daily for 28 days. Studies have determined that mid-summer exposure for 3 hours is equally effective.

Objectives: To determine the effect of 3 hours sun exposure daily in the heliotherapy of psoriasis at the Dead Sea during the months March to December; and to monitor the associated ambient doses of solar UVB radiation.

Methods: A total of 194 patients with moderate to severe psoriasis was treated in the months of March to December by 3 hours of sun exposure each day. The dose of ambient solar UVB was monitored by a Solar Model 501A UVB-Biometer.

Results: Three hours of sun exposure daily was therapeutically efficacious in all months from March to November, but not in December. The lowest effective cumulative UVB dose was 170 SED (standard erythema dose), recorded in March and November.

Conclusions: Daily sun exposure for the heliotherapy of psoriasis at the Dead Sea can be reduced to at least 3 hours daily, about half the time originally recommended.