Sun protection with clothing
Authors: B.L. Diffey
Journal: British Journal of Dermatology (2001)

One consequence of the increasing concern about sun exposure is that it has resulted in methods to determine the ultraviolet (UV) protection afforded by clothing fabrics and the introduction of the so-called Ultraviolet Protection Factor (UPF),1 which is analogous to the ubiquitous Sun Protection Factor (SPF) associated with sunscreens. The common method of determining the UPF is to use an in vitro method. Briefly, this method utilises a source of UV radiation and a photodetector to measure the UV intensity before and after passing through the fabric sample. The ratio of these two measurements is numerically equal to the UPF. Gambichler and colleagues2 have compared this methodology with in vivo determination of UPF using erythema as the endpoint and found that agreement differed depending upon whether the clothing was in direct contact with the skin, or a few millimetres off the skin; a situation that most often pertains in practice. Reassuringly, they found that laboratory in vitro testing gave results that were in good agreement with the off-skin in vivo data. The clothing industry has embraced the notion of sun protection and UPFs, and there is now a British Standard for its measurement,3 with many specialist companies providing sun-protective clothing, but are the interests of public health really served by protection factors assigned to clothing and the perception that 'ordinary' clothing is not good enough if we want to avoid skin cancer? Sunscreens applied at the thickness tested by manufacturers need only possess a SPF of 15 to prevent sunburn even for allday exposure in tropical sunshine, yet behavioural studies show that high SPF (> 15) sunscreens do not always prevent sunburn.4 That the protection achieved is often less than that expected depends upon a number of factors: application thickness and technique; type of sunscreen applied; resistance to water immersion and sand abrasion; and when, where and how often sunscreen is re-applied. A useful rule-of-thumb is that the protection most people get from a sunscreen is equal to about one-third the SPF. So applying a SPF15 sunscreen at a typical application thickness to the face provides about 5-fold protection, much the same as wearing a broad-brim hat.5 Clothing, on the other hand, does not suffer from the uncertainties of sunscreen application, and a fabric whose UPF is 15, say, really does provide this level of sun protection. National radiation laboratories in Australia and the UK have determined UPFs on several thousand summerweight clothing fabrics with the following results:6, 7 almost 90% of summer clothing has UPF > 10 and, in practice, provides equivalent protection to sunscreens of SPF 30 or higher; and 80% of summer clothing has UPF > 15 and under normal exposure patterns will offer virtually complete protection. There is a real danger in labelling clothing with UPFs because it can be argued that consumers do not want to make choices about something they don't understand but are concerned, nonetheless, that the information given on the label is important to their health. Surveys by the Health Education Authority8 have revealed considerable confusion about the meaning of some of the terms used on sunscreen bottle labels, almost no understanding of what ultraviolet radiation does and what sunscreens do in relation to it, and only the vaguest understanding of SPF numbers. Rather than reassure and inform the public, a labelling system for clothing may simply give rise to anxiety and confusion. Will a parent who doesn't purchase high protection (and probably expensive) clothing for his/her child be deemed, either by themselves or others, to be putting the child at unnecessary risk of skin cancer?