Sunscreen protection in the ultraviolet A region: how to measure the effectiveness

Abstract

Products containing ultraviolet (UV) radiation absorbing or scattering ingredients provide varying degrees of protection from sunlight (or other UV sources), thus minimizing the deleterious effects on the skin. The ''sun protection factor'' (SPF) of sunscreen products has become a well recognized indicator of protection against sunburn induced predominantly by ultraviolet B radiation (UVB: 290-320 nm). A similar system of denoting sunscreen protection from ultraviolet A (UVA: 320-400 nm) radiation has not been universally recognized. A variety of test methods have been proposed, both in vitro and in vivo, each with specific virtues and shortcomings. RegulaThe major source of UVA damage -sunlight: its spectra and variation with season There are many misconceptions about the intensity and doses of UV radiation that constitute our daily exposure risk. While there is a greater prevalence of UVA radiation in the sun's spectrum compared with UVB, the intensity is not constant during the day or during the year. Table 1 and Fig. 1 shows the variation of both UVB and UVA during the day and over the seasons as measured in Central New Jersey (40ae N. Lat.) on clear days on or about the summer solstice, the vernal and autumnal equinoxes, and the winter solstice. They show that the UVA daily doses in the winter are only half that of a summer, spring, or fall day. The intensity of UVA is similarly only about half that experienced on a summer day. This is due to the lower sun angle during the winter as well as the shorter daylight hours from the earth's tilt on its axis during the winter.The UVB radiation changes more dramatically than the UVA radiation during the daytime as well as over the seasons as it is absorbed preferentially by the ozone in the stratosphere (longer pathlength during the winter and at low sun angles at the beginning and end of the day, resulting in lower UVB dose reaching the earth's surface).2 tory agencies and industry have been reviewing the available methods over the past decade in an effort to develop consumer meaningful claims and appropriate substantiation methods. This article reviews these test methodologies, in vitro and in vivo, as well as the biological background that establishes the need for UVA protection, and the UVA content of solar radiation and its variability.

UV-induced skin cancer at workplace and evidence-based prevention

“…Data from Central New Jersey have shown that in winter the UVA daily doses are only half that of a summer, spring or fall day. The UVB radiation changes more dramatically than the UVA radiation during the daytime as well as over the seasons as it is absorbed preferentially by the ozone in the stratosphere (longer path length during the winter and at low sun angles at the beginning and end of the day, resulting in lower UVB dose reaching the earth's surface) (Cole 2001).…”

In vitro assessments of UVA protection by popular sunscreens available in the United States

“…Five products (Nos. 3,7,8,12,13) achieved the high category (3 stars). No products qualified for the ''highest'' category with the 4-stars rating.…”

Dosimeter based on 8-methoxypsoralen for UVA exposures over extended periods

“…This was the boundary used in this research to define the UVA waveband although the wavelength boundary between the UVB and UVA is defined at both 315 nm and 320 nm. The CIE [27] defines the boundary as 315 nm; however 320 nm is employed in a significant number of publications, due largely to the biological significance of wavelengths between 315 and 320 nm [28,29]. …”