Curtis Cole

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

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. Regulatory 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.

High-SPF sunscreens (SPF ≥ 70) may provide ultraviolet protection above minimal recommended levels by adequately compensating for lower sunscreen user application amounts

BACKGROUND The manner in which consumers apply sunscreens is often inadequate for ultraviolet protection according to the labeled sun protection factor (SPF). Although sunscreen SPFs are labeled by testing at an application density of 2 mg/cm(2), the actual protection received is often substantially less because of consumer application densities ranging from 0.5 to 1 mg/cm(2). High-SPF sunscreens may provide more adequate protection even when applied by consumers at inadequate amounts. OBJECTIVE We sought to measure the actual SPF values of various sunscreens (labeled SPF 30-100) applied in amounts typical of those used by consumers. METHODS Actual SPF values were measured on human volunteers for 6 sunscreen products with labeled SPF values ranging from 30 to 100, applied at 0.5, 1.0, 1.5, and 2.0 mg/cm(2). RESULTS There was a linear relationship between application density and the actual SPF; sunscreens with labeled SPF values of 70 and above provided significant protection, even at the low application densities typically applied by consumers. Sunscreens labeled SPF 70 and 100 applied at 0.5 mg/cm(2) provided an actual SPF value of, respectively, 19 and 27. LIMITATIONS The study was conducted in a laboratory setting under standardized conditions and results are extrapolated to actual in-use situations. CONCLUSION Sunscreens with SPF 70 and above add additional clinical benefits when applied by consumers at typically used amounts, by delivering an actual SPF that meets the minimum SPF levels recommended for skin cancer and photodamage prevention. In contrast, sunscreens with SPF 30 or 50 may not produce sufficient protection at actual consumer usage levels.

Multicenter evaluation of sunscreen UVA protectiveness with the protection factor test method

BACKGROUND Currently there is no consensus on a test method to determine the protectiveness of sunscreens in the UVA region alone. OBJECTIVE The protection factor in UVA (PFA) test method was evaluated to determine its ability to detect dose-response, specificity for UVA protection only, and repeatability between laboratories, and to detect whether the protection factors depended on the skin response observed (erythema or tanning). METHODS Sunscreens containing 0%, 2%, or 5% oxybenzone, or 7% octyl dimethyl para-aminobenzoic acid were tested by the PFA protocol in five laboratories. RESULTS The test method demonstrated ability to distinguish differences between the protection in the oxybenzone formulations but not between the placebo (0%) and the 7% octyl dimethyl para-aminobenzoic acid formula. The protection factors were independent of the type of skin response. CONCLUSION These data support the utility and validity of the PFA method for determining the UVA protection provided by sunscreen products.

New noninvasive approach assessing in vivo sun protection factor (SPF) using diffuse reflectance spectroscopy (DRS) and in vitro transmission.

In the past 56 years, many different in vitro methodologies have been developed and published to assess the sun protection factor (SPF) of products, but there is no method that has 1 : 1 correlation with in vivo measurements. Spectroscopic techniques have been used to noninvasively assess the UVA protection factor with good correlation to in vivo UVA‐PF methodologies.

Diffuse reflectance spectroscopy for ultraviolet A protection factor measurement: correlation studies between in vitro and in vivo measurements

Background/purpose: Assessing the ultraviolet (UVA) protection factor of sunscreen formulations has been discussed for the past 20 years. The purpose of this study is to correlate the measurements of the UVA protection factor value (PFA value) via in vivo diffuse reflectance spectroscopy (DRS) and to compare this method with the in vitro method of measuring the PFA value, as well as with the in vivo persistent pigment darkening (PPD) and PFA methodologies.

A broad spectrum high-SPF photostable sunscreen with a high UVA-PF can protect against cellular damage at high UV exposure doses.

Advances in sunscreen technologies have yielded broad spectrum sunscreens at high‐sun protection factor (SPF) and ultraviolet A protection factor (UVA‐PF) levels that are photostable and powerful in protecting skin from erythema. Questions arise whether these sunscreens protect proportionally against cellular skin damage caused by high ultraviolet exposures.

Metal oxide sunscreens protect skin by absorption, not by reflection or scattering

The inorganic metal oxide sunscreens titanium dioxide and zinc oxide have been considered to protect against sunburning ultraviolet radiation by physically reflecting/scattering the incident photons and thus protecting the skin. Earlier publications suggested, however, that the primary action of UV protection by these sunscreen agents is through absorption and not by reflection. The purpose of this work was to quantitate the contributions of each of these modes of action to the protection provided by inorganic UV sunscreen filters.

Sunscreens--what is the ideal testing model?

Sunscreen protection assessment methodologies have been evolving in tandem with the innovation and evolution of sunscreen products themselves; from initial human testing in the Swiss Alps, to laboratory testing with high intensity solar simulators, to spectrophotometers with modern CCD array photocells and diffuse reflectance spectroscopy techniques. The progress in the science leads regulatory development of standard methods, and provides new and improved ways to assess sunscreen protection properties. This review scans much of the history of the development of these methods and highlights the latest development in non‐invasive sunscreen testing as an opportunity to improve accuracy while eliminating human UV exposures.

An evaluation of ultraviolet A protection and photo-stability of sunscreens marketed in Australia and New Zealand.

To the Editor, The population in Australia and New Zealand is at a higher risk of acute and chronic ultraviolet A (UVA) damage due to both geographic as well as genetic factors. Table 1 lists sunscreens purchased in these regions that we recently tested, along with the active ingredients and their respective concentrations. We investigated UVA protection level as well as UVA photo-stability of these products as they represent the most widely used sun protection products in Australia/New Zealand and because they all contain the active ingredient butyl methoxydienzolmethane (avobenzone), a potent UVA absorber that is photo-labile. A known photo-stable sunscreen from the US market was included in the table as a reference point. In vivo UVA protection factors (UVAPF) for these sunscreens were measured with persistent pigment darkening method outlined by Japanese Cosmetic Industry Association (1). In vitro UVAPF were determined according to the COLIPA Guidelines (2). UVA photo-stability tests were conducted by comparing the COLIPA in vitro UVAPF of the sunscreens before and after 50 J/cm of solar-simulated irradiation. In vivo and in vitro UVAPFs, as well as photo-stability results were included in Table 1 for these sunscreens. It is noteworthy that while all of the test products claim SPF 301 and broad-spectrum UVA/UVB protection, the UVAPF for these sunscreens ranges from 5 to 9. Equally important is the fact that none of the tested sunscreens were photo-stable in the UVA region. The remaining UVA protection (as measured by UVAPF) after 50 J/cm of UV irradiation ranged from 27 to 57% of the initial UVAPF. The poor photo-stability may be partly due to the fact that all these popular Australian/New Zealand sunscreens contain octyl methoxycinnamate (octinoxate), an ingredient known to enhance the photo-degradation of avobenzone (3). While these widely used sunscreens in Australia and New Zealand likely supply the protection level claimed on the label as demonstrated in qualifying SPF test, they have inadequate overall performance in UVA protection. UV damage, particularly UVA damage, can occur with sub-erythemal dose and can be accumulative, resulting in chronic photoaging. UVAPF values of 5–6 do not translate to adequate levels of UVA protection in reality when consumers under-apply the sunscreen. In addition, UVA protection of these sunscreens continues to weaken during sun exposure as the UVAPF values degrade continuously even before the first erythema reaction happens. Even if consumers wearing these sunscreens did not stay long enough under the sun to get sunburn, the initial UVA protection level consumers received when they first applied the sunscreen would be significantly compromised during the first few hours of sun exposure.

Multi-laboratory validation of very high sun protection factor values

Background: High sun protection factor (SPF) sunscreens have multiple benefits but there has not been validation of the test method for determining SPF values higher than 50. This study addresses specifically the accuracy and reproducibility of the high SPF test.