Behavioral Strategies Recommended to Reduce Risk for Skin Cancer

May 9, 2007 — Limiting exposure to the sun and wearing sun-protective clothes are the most effective ways to reduce risk for skin cancer, compared with using sunscreens, according to the results of a review published in the May 3 Early Online Publication issue of The Lancet.

"Sun exposure is the main cause of photocarcinogenesis, photoageing, and photosensitivity; thus, photoprotection is an important issue," write Stephan Lautenschlager, from Triemli Hospital in Zurich, Switzerland, and colleagues. "In a skin cancer prevention strategy, behavioural measures — eg, wearing sun protective clothes and a hat and reducing sun exposure to a minimum — should be preferred to sunscreens. Often this solution is deemed to be unacceptable in our global, outdoor society, and sunscreens could become the predominant mode of sun protection for various societal reasons (eg, healthiness of a tan, relaxation in the sun)."

Unprotected exposure to UV radiation from the sun is a major risk factor for developing skin cancer, as well as skin aging and photodermatoses. Although UVB is the waveband region causing direct photochemical damage to DNA, and hence gene mutations, UVA may have more indirect effects on DNA via the generation of reactive oxygen species. UVA may also have an important role in the pathogenesis of melanoma. Whereas UVA has a greater role in long-term sun damage, UVB is more important for short-term effects of sun exposure, such as sunburn or vitamin D synthesis.

Preventive strategies highlighted in this review, in decreasing order of effectiveness and lifestyle disruption, are completely avoiding exposure to the sun, seeking shade at times when disease-inducing wavelengths are relatively intense, wearing clothes that protect against UV radiation penetration, and using topical sunscreens.

The authors searched MEDLINE from 1990 to August 2006 for articles published in English, French, and German with the keywords "sunscreen," "photoprotection," and "sun protection" and placed special focus on work published within the past 3 years. They also searched articles through Scopus from 1998 to the present and without language restriction, using the term "sunprotection," as well as several review articles and book chapters.

Because sun exposure is the primary cause of photocarcinogenesis, photoaging, and photosensitivity, protection from UV radiation in sunlight is of vital importance. According to the authors, behavioral measures, such as wearing sun-protective clothes and a hat and minimizing sun exposure, are preferred over sunscreens to prevent skin cancer.

Factors that increase sun protection of fabrics include tightly woven fibers, thicker fabrics (eg, denim, wool, and synthetic materials such as polyester), loosely fitting materials, dry materials, fabrics that shrink after washing, fabrics treated with a broad-spectrum UV absorber (eg, Tinosorb; Ciba Specialty Chemicals, Basel Switzerland), dark-colored fabrics, and unbleached fabrics.

When midday summer exposure or tropical exposure is unavoidable, and even during times of less intense sun exposure, protective clothes should cover as much of the skin surface as possible, and a highly protective sunscreen should be applied properly over the remainder of the exposed skin.

The sun protection factor (SPF), a widely accepted method of measuring sunscreen efficacy, is defined as the sun radiation dose (mainly UVB) required to produce the minimum erythemal dose (threshold dose that can produce sunburn) after the application of 2 mg/cm2 of sunscreen divided by the dose producing 1 minimum erythemal dose on unprotected skin. An SPF of 2 therefore absorbs 50% of UV radiation; SPF 8 sunscreen, 87.5%; and SPF 16 sunscreen, 93.6%.

Because studies have shown that high-SPF sunscreen is preferable to low-SPF sunscreen, broad-spectrum sunscreens with adequate UVA protection are recommended, despite the absence of a clear definition of what is determined to be adequate. The SPFs and UVA/UVB spectra of available sunscreens differ worldwide. However, sunscreens of any type should not be abused in an attempt to maximize time spent in the sun.

To maximize the effectiveness of sunscreen, it should be applied uniformly over the exposed skin surface in liberal quantities. The specific absorption spectrum of the agent used is an important consideration; high-SPF sunscreens (SPF > 15) offer better protection against UVB than do low-SPF sunscreens, but this has not been clearly proven to further protect against skin cancer.

Organic sunscreens should be applied to exposed sites 15 to 30 minutes before sun exposure. Waterproof or water-resistant sunscreens should be used to reduce the need for reapplication after swimming followed by drying with a towel, friction from clothing or sand, and sweating.

In areas with low sun exposure, such as the United Kingdom and northern Europe, year-round, daily use of sunscreen cannot be recommended. During October to March, sunscreen use should be avoided in such locales. However, there is evidence to suggest that the year-round application of sunscreens can help prevent cancer and solar elastosis in areas of high insolation, such as Queensland, Australia, and Texas, United States.

Adverse reactions from sunscreen ingredients appear to be increasing in frequency, occurring in as many as 19% of individuals in 1 recent Australian study. These include allergic and irritant contact dermatitis, phototoxic and photoallergic reactions, contact urticaria, and even occasional severe anaphylactic reactions. Most adverse reactions to sunscreens are caused by irritant, rather than allergic, reactions to either the sunscreen agents or the base.

"To anticipate that newer formulations of sunscreens will lead to a benefit as a protective agent against melanoma is reasonable, although such a benefit might not be seen for several decades," the authors conclude. "However, their use in practice could be difficult, time consuming, and expensive, and they can, in general, be used only in addition to the more reliable measures of clothing protection and reduction of ultraviolet exposure during peak hours of solar radiation."

The authors have disclosed no relevant financial relationships.

Lancet. Published online May 3, 2007.

Source: http://www.medscape.com/viewarticle/556250?src=mp