© 2000 by Oxford University Press
Journal of the National Cancer Institute, Vol. 92, No. 18, 1532-1533,
September 20, 2000
© 2000 Oxford University Press
CORRESPONDENCE |
RESPONSE More About: Sunscreen Use and Duration of Sun Exposure: a Double-Blind, Randomized Trial
Affiliations of authors: P. Autier, G. Severi, P. Boyle, Division of Epidemiology and Biostatistics, European Institute of Oncology, Milan, Italy; J.-F. Doré, Institut National de la Santé et de la Recherche Médicale, Unit 453, Centre Léon Bérard, Lyon, France.
Correspondence to: Philippe Autier, M.D., M.P.H., Division of Epidemiology and Biostatistics, European Institute of Oncology, Via Ripamonti 435, Milan 20141, Italy (e-mail: pautier{at}ieo.it).
The correspondence by Young raises a number of points, some of which are easily addressed technical issues and others that are speculative.
The fact that the trial (1) achieved a well-balanced randomization for all practical purposes rules out the possibility that the difference in sun exposure duration could proceed from a difference in sun sensitivity between the two randomization groups.
Young's assessment that participants did not receive enough sunscreen is incorrect. We intentionally provided participants with a quantity of sunscreen in considerable excess of the amount habitually used by most people. In fact, all of the participants came back with more than half of the sunscreen they received at the start of the study. From the daily record diaries, we calculated that participants used, on average, 0.5 mg/cm2 of sunscreen, a figure often found in the literature (2).
Retardation of sunburn occurrence was the obvious clinical end point proposed by Young. Sunscreens have been primarily designed to prevent sunburns. It simply took a longer time for participants who used the sun protection factor (SPF) 30 sunscreen to get a sunburn. Although the participants who used SPF 30 remained longer in the sun, they experienced the same number of sunburn episodes as the participants who used SPF 10. This phenomenon poses a major public health concern, since, as Young correctly mentions, our trial also suggested that extension of sunbathing activities induced by sunscreen use was more pronounced in sun-sensitive participants [see Table 2 in (1)].
The SPF is an indicator derived from laboratory testing. Young's reasoning on SPF is speculative, since it relies only on the experimental definition of SPF and does not take into account that participants who used SPF 30 also tended to sunbathe when the ultraviolet B radiation was greatest and that participants who used SPF 30 tended to adopt more hazardous sun exposure behaviors, as evidenced by women sunbathing with naked breasts.
For various reasons, speculation on the virtues of sunscreen in real life based on laboratory experiments is common, even if we don't know how a given laboratory result fits into the as yet unknown pathways between sun exposure and melanoma. In the past, such extrapolations were used to justify the addition of 5-methoxypsoralen (5-MOP), a tanning activator and known photocarcinogen in sunscreen preparations (3). Despite warnings from several scientists (4), these laboratory data were used to support the marketing of 5-MOP sunscreens in France, Belgium, and Greece, until they were banned by the European Commission in 1995, after an epidemiologic investigation (5) showed a direct greater melanoma risk among subjects who used 5-MOP sunscreens, especially if they were naturally sun sensitive.
Young concludes that people need to be educated on how to use sunscreens. But do we know what the correct use of these products is? When sun exposure is unintentional—i.e., not motivated by acquisition of a tan (e.g., gardening or skiing)—use of a sunscreen seems to decrease the incidence of sunburn, actinic keratosis, and squamous cell cancer of the skin, and the protection conferred correlates with the quantities used (6,7).
In intentional sun exposure, motivated by the acquisition of a tan, sunscreen use appears to increase melanoma incidence because it may encourage subjects to stay longer in the sun (2). In that respect, use of greater quantities of sunscreen during intentional sun exposure could well result in even longer sun exposures. The primary rule that guides medical practice is "First, do no harm" (Hippocrates, 460–375 B.C.). Hence, one should avoid promoting sunscreen use for intentional exposure to the sun (see www.iarc.fr for details).
RREFERENCES
1 Autier P, Dore JF, Negrier S, Lienard D, Panizzon R, Lejeune FJ, et al. Sunscreen use and duration of sun exposure: a double-blind, randomized trial. J Natl Cancer Inst 1999;15:1304–9.cancerlit;99362510
2
Diffey B. Has the sun protection factor had its day? BMJ 2000;320:176–7.
3 Young AR, Potten CS, Chadwick CA, Murphy GM, Hawk JL, Cohen AJ. Photoprotection and 5-MOP photochemoprotection from UVR-induced DNA damage in humans: the role of skin type. J Invest Dermatol 1991;97:942–8.[CrossRef][Web of Science][Medline]cancerlit;92013252
4
Morison WL. In reply: To tan or not to tan. Arch Dermatol 1990;126:681–2.
5 Autier P, Dore JF, Schifflers E, Cesarini JP, Bollderts A, Koelmel KF, et al. Melanoma and use of sunscreens: an EORTC case–control study in Germany, Belgium and France. The EORTC Melanoma Cooperative Group. Int J Cancer 1995;61:749–55.[Web of Science][Medline]cancerlit;95310049
6 Green A, Williams G, Neale R, Hart V, Leslie D, Parsons P, et al. Daily sunscreen application and betacarotene supplementation in prevention of basal-cell and squamous-cell carcinomas of the skin: a randomised controlled trial [published erratum appears in Lancet 1999;354:1038]. Lancet 1999;354:723–9.[CrossRef][Web of Science][Medline]cancerlit;99402168
7
Naylor MF, Boyd A, Smith DW, Cameron GS, Hubbard D, Neldner KH. High sun protection factor sunscreens in the suppression of actinic neoplasia. Arch Dermatol 1995;131:170–5.
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