LETTERS * CORRESPONDANCE
We will consider for publication only letters submitted in duplicate, printed in letterquality type without proportional spacing and not exceeding 450 words. All the authors must sign a covering letter transferring copyright. Letters must not duplicate material being submitted elsewhere or already published. We routinely correspond only with authors of accepted letters. Rejected letters are destroyed. Accepted letters are subject to editing and abridgement.
Seules peuvent etre retenues pour publication les lettres recues en double dont la longueur n'excede pas 450 mots. Elles doivent etre mecanographi&es en qualite (> sans espacement proportionnel. Tous les auteurs doivent signer une lettre d'accompagnement portant cession des droits d'auteur. Les lettres ne doivent rien contenir qui ait ete presente ailleurs pour publication ou dej& paru. En principe, la redaction correspond uniquement avec les auteurs des lettres retenues pour publication. Les lettres refusees sont detruites. Les lettres retenues peuvent etre abregees ou faire l'objet de modifications d'ordre redactionnel.
Protection against ultraviolet radiation T n he effects of the sun on the skin are quite rightly given "headline billing" on the cover of the Apr. 15, 1992, issue
of CMAJ. Unfortunately, although the epidemiologic importance of excessive sun exposure is forcefully and accurately outlined in "MDs and ozone depletion: Be careful not to turn patients into 'cancerphobes'," by Dr. Peter P. Morgan (146: 1397-1399), the important details of sunscreen use are presented vaguely. There is widespread confusion among the public and even among physicians about which sunscreen to recommend, and certainly CMAJ should not compound this confusion. SEPTEMBER 15, 1992
I really don't know what an "industrial-strength sun blocker" is. The sun protection factor (SPF), and not the "blocking factor" mentioned in the article, is the measure of protection against short-wave ultraviolet radiation (UVB). The number implies relative protection; for example, with an SPF of 15 approximately 1/15th of the UVB penetrates the skin. However, there may not be much greater protection with higher SPFs, and the accuracy of the higher numbers is questionable. I recommend that my patients use something with an SPF of at least 15, but I don't insist on higher numbers. It is extremely difficult to quantify penetration of the skin by long-wave ultraviolet radiation (UVA), and the claims of many sunscreens to protect against UVA are not supported by clinical data. Avobenzone (Parsol 1789), currently in only two of the sunscreens in Canada (which are somewhat more expensive than most of the competition), has shown the best available protection against UVA apart from that provided by opaque true "sunblocks." Although UVA has long-term damaging effects on the skin, the prime culprit, as far as is known, is UVB. Thus, if cost is a significant impediment the use of a reputable UVB sunscreen is appropriate. Ignored in the article is substantivity - that is, how well the sunscreen stays on the skin. A greasy sunscreen is best for someone engaging in water sports or likely to sweat profusely but is unacceptable on the face, where it may stimulate the development of acne or come into contact with the eyes and cause stinging.
It should be emphasized to patients that sunscreens are only an adjunct in protection and should not be used as a means to achieve lengthy exposure to sunlight. Finally, Dr. Donald Rosenthal, whom Dr. Morgan quotes, is a Hamilton, not Ottawa, dermatologist. John Goodall, MD, FRCPC Ottawa, Ont.
The frequent reports in the news media about the dangers of excessive exposure to sunlight continually remind and frighten people about the possibility of getting skin cancer. However, these reports do not discuss the connection between people's nutritional health and their susceptibility to cancer of the skin. Since ultraviolet radiation increases the formation of free radicals it would not be surprising if an increase in the availability of antioxidants prevented some of the toxic reactions to ultraviolet radiation. Selenium is such a preventive nutrient. Burke and colleagues' reported that a lotion containing 0.02% L-selenomethionine or water containing 1.2 parts per million of this substance when given to hairless, pigmented mice protected them against damage from ultraviolet radiation. These doses did not cause any toxic reactions. The authors concluded that "L-selenomethionine is effective in protecting against skin cancer . . . both by retarding the onset and reducing the number of lesions and . . . in reducing the acute damage induced by UV ir-
radiation-inflammation (sunburn), blistering, and pigmentation (tanning)." No blisters develCAN MED ASSOC J 1992; 147 (6)
839
We will consider for publication only letters submitted in duplicate, printed in letterquality type without proportional spacing and not exceeding 450 words. All the authors must sign a covering letter transferring copyright. Letters must not duplicate material being submitted elsewhere or already published. We routinely correspond only with authors of accepted letters. Rejected letters are destroyed. Accepted letters are subject to editing and abridgement.
Seules peuvent etre retenues pour publication les lettres recues en double dont la longueur n'excede pas 450 mots. Elles doivent etre mecanographi&es en qualite (> sans espacement proportionnel. Tous les auteurs doivent signer une lettre d'accompagnement portant cession des droits d'auteur. Les lettres ne doivent rien contenir qui ait ete presente ailleurs pour publication ou dej& paru. En principe, la redaction correspond uniquement avec les auteurs des lettres retenues pour publication. Les lettres refusees sont detruites. Les lettres retenues peuvent etre abregees ou faire l'objet de modifications d'ordre redactionnel.
Protection against ultraviolet radiation T n he effects of the sun on the skin are quite rightly given "headline billing" on the cover of the Apr. 15, 1992, issue
of CMAJ. Unfortunately, although the epidemiologic importance of excessive sun exposure is forcefully and accurately outlined in "MDs and ozone depletion: Be careful not to turn patients into 'cancerphobes'," by Dr. Peter P. Morgan (146: 1397-1399), the important details of sunscreen use are presented vaguely. There is widespread confusion among the public and even among physicians about which sunscreen to recommend, and certainly CMAJ should not compound this confusion. SEPTEMBER 15, 1992
I really don't know what an "industrial-strength sun blocker" is. The sun protection factor (SPF), and not the "blocking factor" mentioned in the article, is the measure of protection against short-wave ultraviolet radiation (UVB). The number implies relative protection; for example, with an SPF of 15 approximately 1/15th of the UVB penetrates the skin. However, there may not be much greater protection with higher SPFs, and the accuracy of the higher numbers is questionable. I recommend that my patients use something with an SPF of at least 15, but I don't insist on higher numbers. It is extremely difficult to quantify penetration of the skin by long-wave ultraviolet radiation (UVA), and the claims of many sunscreens to protect against UVA are not supported by clinical data. Avobenzone (Parsol 1789), currently in only two of the sunscreens in Canada (which are somewhat more expensive than most of the competition), has shown the best available protection against UVA apart from that provided by opaque true "sunblocks." Although UVA has long-term damaging effects on the skin, the prime culprit, as far as is known, is UVB. Thus, if cost is a significant impediment the use of a reputable UVB sunscreen is appropriate. Ignored in the article is substantivity - that is, how well the sunscreen stays on the skin. A greasy sunscreen is best for someone engaging in water sports or likely to sweat profusely but is unacceptable on the face, where it may stimulate the development of acne or come into contact with the eyes and cause stinging.
It should be emphasized to patients that sunscreens are only an adjunct in protection and should not be used as a means to achieve lengthy exposure to sunlight. Finally, Dr. Donald Rosenthal, whom Dr. Morgan quotes, is a Hamilton, not Ottawa, dermatologist. John Goodall, MD, FRCPC Ottawa, Ont.
The frequent reports in the news media about the dangers of excessive exposure to sunlight continually remind and frighten people about the possibility of getting skin cancer. However, these reports do not discuss the connection between people's nutritional health and their susceptibility to cancer of the skin. Since ultraviolet radiation increases the formation of free radicals it would not be surprising if an increase in the availability of antioxidants prevented some of the toxic reactions to ultraviolet radiation. Selenium is such a preventive nutrient. Burke and colleagues' reported that a lotion containing 0.02% L-selenomethionine or water containing 1.2 parts per million of this substance when given to hairless, pigmented mice protected them against damage from ultraviolet radiation. These doses did not cause any toxic reactions. The authors concluded that "L-selenomethionine is effective in protecting against skin cancer . . . both by retarding the onset and reducing the number of lesions and . . . in reducing the acute damage induced by UV ir-
radiation-inflammation (sunburn), blistering, and pigmentation (tanning)." No blisters develCAN MED ASSOC J 1992; 147 (6)
839
