Hao Ou-Yang

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.

Diurnal and seasonal variations of the UV cut-off wavelength and most erythemally effective wavelength of solar spectra

Background Biologically effective solar ultraviolet radiation is defined as the product of the intensity of the solar spectrum and the erythema action spectrum at each wavelength. In this way we may arrive at the weighted effectiveness of each wavelength of solar radiation to produce a sunburn reaction. There have been many measurements of the variation of the solar spectrum with the time of the day and the time of the year, but questions remain as to the variation of the quality of the spectrum and the contribution of the shortest wavelengths of solar terrestrial radiation. The purpose of the present study was to determine the variation of the biologically effective solar spectrum with the time of the day and the time of the year and to determine the variation of the shortest wavelength that contributes to the sunburn reaction with the time of the day and the time of the year.

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.

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.

Sunscreen formulations may serve as additional water barrier on skin surface: A clinical assessment

Extended water exposure can cause stratum corneum swelling and a more porous skin barrier. People often wear water‐resistant sunscreen formulations during extended period of water activities in the summer to protect skin from harmful UV rays. We wanted to evaluate whether sunscreen formulations can also serve as additional water barriers to help mitigate the disruption in stratum corneum caused by constant exposure to water.

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.

Sunscreen formulations do not interfere with sweat cooling during exercise

Sweating plays a critical role in maintaining thermal balance and keeping skin cool during exercise. People often wear sunscreens on hot summer days for sun protection. Most recreational sunscreens are designed to be water‐ and sweat‐resistant, so that sweating will not remove or compromise the protection. The objective of this study was to determine whether wearing sweat‐resistant sunscreen might impede natural sweating, potentially interfering with thermal regulation and resulting in the elevation of skin temperature.

Dose-response of SPF values: linear or exponential?

To the Editor, There were multiple clinical studies in recent years examining the dose relationship between the amount of sunscreen applied and the resulting SPF values on skin (1–4). This is because people typically apply 0.5 to 1.5 mg/cm of sunscreen in real life instead of the 2 mg/cm dosage prescribed in SPF test. SPF values generally decreases with less application. However, the question arises why the SPF dose–response curves were more or less linear in some studies (3, 4). In this letter, we try to understand these observations by using an established model and by testing simple formulations in vitro. Application dosage is directly related to film thickness when density is constant, so the question becomes how SPF depends on film thickness. According to Beer’s law, absorbance is linearly related to film thickness (d) and concentration of the filter (c), as well as the extinction coefficient of the sunscreen filter (k): A = log (I/I0) = k*c*d, where I and I0 are transmitted and incoming light intensities. Theoretically, light transmission (I/I0) should increase exponentially with film thickness or application dosage. However, application of sunscreen formulation by human being on a non-flat skin surface often can result in a film that is not perfectly homogeneous. O’Neill first developed a step film model (Fig. 1), which was broadened by others to help understand quantitatively the contribution of film irregularities to absorbance (5–7). In step film model, two parameters, f and g, are used to characterize how irregular is the film (0 < f, g < 1). As shown in Fig. 1, the thickness profile shows a step shape as a result of moving some materials from one area (g) to another (1 g). As the total light transmission through the step film is the addition of transmission in two areas of different thickness: (1 f) * d for g and d+ f * g *d/(1 g) for 1 g, the final transmission can be written as