Phototherapy

For the majority of people with psoriasis, exposure to ultraviolet radiation improves their condition. There are a small minority of around 10% who have light sensitive psoriasis; for them exposure to UV radiation can cause psoriasis to worsen or develop. The term phototherapy includes therapeutic use of both UVA and UVB light. The principle underpinning both wavelengths of UV radiation is that they suppress the immune response within the skin and thus dampen down the cascade of immunological changes which occur to trigger psoriasis. The most concerning side effect on a long-term basis is the development of skin cancer. For this reason, careful monitoring of the cumulative doses administered is important and it is usual to limit the course of treatment given to individuals. Other more immediate side effects can include skin dryness and erythema.

There is mixed evidence about whether emollients should be used prior to UVB and PUVA treatments. Because they reduce scaling it is argued that there is improved penetration of the UV radiation; however, it has been shown that a number of emollients have a UV protective capacity (at different parts of the UV spectrum) and thus reduce the efficacy of the light therapy (Otman et al., 2006). It is also likely that factors such as plaque thickness, how much emollient is applied and when it is applied will have a role to play. The recommendations by Otman et al. (2006) were no more specific than to say that if emollients were to be used prior to UV therapies that they should have minimal UV blocking effects. Box 8.2 shows emollients from the British National Formulary that they found had a sun protection factor of less than 1.2 for UVB, UVA and PUVA. Previous researchers had stated that protection factor of 1.2 or higher represented a reduction in UV transmittance of 17% or more which was thought to be clinically significant (Hudson-Peacock et al., 1994).

Box 8.2 Emollients that have a SPF of less than 1.2 suitable for use with UV therapy Aveeno cream Calmurid cream Dermol 500 lotion Doublebase cream Emulsiderm emollient Emulsifying ointment Oilatum gel