Suboptimal UVA attenuation by broad spectrum sunscreens under outdoor solar conditions contributes to lifetime UVA burden

Abstract

Background: Broad spectrum sunscreens with a sun protection factor (SPF) of 15 or greater are indicated to decrease the risk of skin cancer and early skin aging caused by the sun if used as directed with other sun protection measures. To determine whether sunscreen product performance is compromised under solar exposure and to test spectral uniformity of protection across the UVA spectrum, we tested broad spectrum sunscreens with a variety of active pharmaceutical ingredients (APIs) and in a variety of dosage forms.

Methods: A cross-sectional market survey of 32 sunscreen drug products containing either organic or inorganic APIs with SPFs of 15, 30, 50, and 70 was tested. UV doses were delivered via natural sun in Silver Spring, Maryland between June and September of 2017.

Results: Of the 32 sunscreen drug products, 6 products failed to meet their broad spectrum claim under solar exposure. Using FDA's new proposal to strengthen sunscreen broad spectrum requirements, spectral uniformity based on the mean sunscreen absorbance of UVA1(340-400 nm)/UV (290-400 nm) indicated that ~40% of sunscreen drug products tested had suboptimal UVA protection.

Conclusion: US consumers may unknowingly be receiving up to 36% more transmitted UVA when selecting between similarly labeled broad spectrum sunscreen drug products with equivalent SPF values. FDA's new proposal may help decrease consumers' overall lifetime UVA burden. Spectral absorbance data on sunscreen performance can be used to further improve the coupling of broad spectrum protection to a product's SPF value so that consumers have improved proportional increases in UV protection.

Keywords: broad spectrum; skin cancer; sun protection factor; sunscreen; ultraviolet radiation.

Figure 1.

(a) Spectral irradiance from the sun versus wavelength for solar exposures between June 28 and Sept 28, 2017 in Silver Spring, Maryland (latitude 39.0 N). (b) Weather conditions including humidity (left y-axis), temperature (left y-axis), and UV Index (right y-axis) during solar exposure pre-irradiations of sunscreen samples. During the intent-to-stress arm of the study, fluctuation in humidity (c) and temperature (d) inside a motor vehicle exposed to the sun for one week was recorded by Hygrometer/Thermometer.

Figure 2.

Spectral profiles of OTC sunscreen drug products after solar exposure. Examples of absorbance profiles of broad spectrum SPF 15 (#SP1 and #L1) (a), 30 (#L9 and #L5) (b), 50 (#L15 and #L12) (c), 70 (#L20 and #L19) (d) sunscreen drug products exhibiting high spectral uniformity vs low spectral uniformity. Mean spectral photoinstability of organic (e) and inorganic (f) sunscreen APIs after an 800 J/m²-ery eff UV dose from the sun.