Aerosol sunscreen sprays, favoured by many for their convenience and ease of application, are not included in Which? sun cream tests due to significant concerns about their real-world effectiveness compared to laboratory results. The consumer champion highlights a potential gap between how these products are assessed in controlled environments and how consumers actually use them outdoors.
Manufacturers typically determine the SPF of aerosol sunscreens using international standard (ISO) methods, which involve 'degassing' the product to remove propellants before testing the remaining liquid. This process, according to Which?, creates an idealised scenario that may not accurately reflect the amount of sunscreen formulation that reaches the skin during typical use. The issue stems from the fact that each spray releases both sunscreen and propellant gas, meaning the actual amount of active product delivered can vary widely.
Further insights into the composition of these sprays come from a 2020 report by the Queensland University of Technology, conducted with assistance from Cancer Council Victoria and ARPANSA (Australian Radiation Protection and Nuclear Safety Agency). This study, which tested nine different aerosol sunscreens, found that propellants constituted between 27% and 83% of the can's contents. Consequently, the duration required to apply the recommended amount of sunscreen can vary dramatically between brands, with some needing four seconds per limb and others up to 14 seconds.
Beyond the propellant issue, environmental factors like wind speed can significantly impact the efficacy of spray sunscreens. Studies indicate that 'overspray,' where fine droplets drift away from the intended target, can lead to substantial product loss. In a light breeze, over a third of the sunscreen may be lost to the air, while this figure can increase dramatically in moderate wind conditions. This is particularly concerning for individuals reapplying sunscreen throughout the day in outdoor settings.
The Australian research also raised questions about the value for money of aerosol sunscreens. Depending on the brand, most cans contained enough sunscreen for only two to three full-body applications. Given recommendations for regular reapplication, a consumer on holiday could potentially use an entire can in a single day, leading to unexpectedly high costs. Additionally, many aerosol cans use propellants, some of which are volatile organic compounds (VOCs) that can contribute to local air pollution, raising sustainability concerns. Consumers are advised to check local authority guidelines for recycling empty aerosol cans.