The Selection and Evaluation of Ultraviolet Absorbers

Abstract

Brisbane SUMMARYThe development and evaluation of chemical agents, intended for use as absorbers of ultraviolet radiation, has made considerable progress since the first sunscreen formulation appeared in 1928. The intended function of these agents is the reduction of erythemogenic radiation, to permit individuals whose skin is not accustomed to the sun to expose themselves to prolonged solar radiation without developing dangerous erythema. The purpose of this paper is to disouss briefly certain aspects of the nature of the agents employed for this purpose, the factors infiuencing their effectiveness, and the methods employed to evaluate the effectiveness. The Ideal SunscreenThe qualities which an ideal sunscreen should possess are shown in Table 1. Kumler andDaniels (1948) andFreeman et al. (1966) have shown that the peak of the so called sunburn curve is at 30S nm. That is, maximum solar erythema production occurs at a wavelength of 308 nm. This value may vary slightly depending npon altitude and in Queensland is around 305 nm. The curve is a rather narrow one with the base extending from ap])roximately 290 to 326 nm. An ideal sunscreen agent will absorb all the radiation in this range and will show its peak absorption between 305 and 308 nm. TABLE lThe Ideal Suvsereen 1. It must filter out tho rays causing sunburn, which are those in the region from 290 to 330 nm. 2. It should be stable in the presence of tight, air, and moisture, or if it is decomposed under these conditions, the decomposition i)rodncts should have comparable absorption to the orignai in tlie 290 to 330 nm. region 3. It should have very slight or no absorption for the long ultraviolet rays beyond 340 nni., which are thought to produce tanning without appreciable erytliema 4. The compound and decomposition products which may be produced under conditions of use should be non-toxic and non-irritating 5. It should be nearly neutral so untoward effects are not produced by the presence of acid or base on the skin 6. It should have good solubility in the ointment base or vehicle in which it is to be formulated and shouJd have a low water solubility to prevent rapid removal by perspiration 7. It should be relatively non-volatile so it wiil not evaporate under conditions of use 8. It should not be rapidly absorbed by the skin For those individuals without abnormal sensitivity to solar radiation, the ideal sunscreen agent will jjermit the transmission of all radiation above 320 nm. Eadiation in tliis range, commonly referred to as the UV-A range, is capable of augmenting pigmentation directly once autogenous pigment formation has been initiated by the UV-B radiation, the range between 290 aud 320 nm. Pigment particles in the skin are darkened by the longer wavelengths, thus increasing the defensive mechanism of the skin against erythema. Individuals vary greatly in their sensitivity to direct pigmentation

Sunscreens – what is the ideal testing model?

“…It was determined early on in sunscreen development that the vehicle and how it formed a film on the skin's surface was critical to efficiency of the UV filters to provide protection. Artificial surfaces were evaluated in order to better mimic thin film sunscreen behavior on the skin including quartz plates mouse epidermis , Transpore™ tape , and Vitro‐Skin® . Each has its own advantages and disadvantages with none achieving a long‐lived endorsement for in vitro SPF testing and validation.…”

Project Sunscreen Protection

“…Early in vitro methods were based on spectrophotometric analysis of dilute sunscreen solutions [24] or measurement of the UV transmission of thin layers of sunscreen sandwiched between quartz plates [25]. It is therefore desirable to have a rapid and reliable in vitro technique that can be used to identify which new sunscreen formulations merit in vivo testing.…”