Effectiveness of heliotherapy for psoriasis clearance in low and mid-latitudinal regions: A theoretical approach

The action spectrum for psoriasis clearance is reconstructed taking into account the results obtained in the early 1980s. The antipsoriatic action spectrum is used for weighting the medical cabinet UV spectra, and the solar spectra measured in San Diego (USA) and Belsk (Poland). The mean cumulative antipsoriatic effective dose of 450 mJ cm−2, due to TL-01 (UVB narrowband) tubes, is taken by a patient with skin phototype II during routine 20 phototherapy sessions carried out in a phototherapy cabinet in the Medical University of Łódz. Thus, the daily mean dose of value 22.5 mJ cm−2 is proposed as the threshold for daily solar dose for numbers of out-door exposures to clear psoriasis. We assume that the heliotherapy will last a whole month with every day 2 h exposition to the direct sunlight around local noon. The heliotherapy will be successful if weather conditions permit at least 20 days with the daily exposure over the threshold. The minimum cumulative ambient erythemal dose, necessary for psoriasis clearance, is estimated as 144 standard erythema dose (SED) for the whole heliotherapy period. We find that heliotherapy could be effectively used in March through October (San Diego) and in June through August (Belsk). Thus, the heliotherapy against psoriasis is possible not only at southern resorts but even at the mid-latitude sites.

► A model of the effectiveness of heliotherapy for psoriasis clearance is developed.
► An analytical formula for the antipsoriatic action spectrum is proposed.
► The antipsoriatic heliotherapy is possible even for typical mid-latitudinal sites.