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Explore health recommendationsThe hidden flaws in spray sunscreens: a Which? scientist explains why we don't test aerosols
Testing spray sunscreens isn't straightforward. Here's why we don't test aerosols, plus our top SPF safety tips
With a PhD in Biology and more than seven years of research experience, Neal develops tests across a range of products and is our in-house sunscreens expert.
Principal researcher/writer at Which? delivering award-winning health, baby and safety investigations, including our annual sunscreen tests.
Aerosol sunscreen sprays are popular for their ‘point-and-shoot’ convenience and ease of application. Who doesn't want that when trying to apply sunscreen to wriggly children or hard-to-reach areas.
However, despite growing demand, aerosol sprays are not included in Which? sun cream tests.
The reason for this is simple: the gap between laboratory results and real-world usage can be significant.
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How are aerosol spray sunscreens tested?
To determine the SPF in the lab, manufacturers use international standard (ISO) methods. These require aerosols to be ‘degassed’, meaning the propellants are removed and the remaining liquid is tested in the same way a lotion or pump-action spray formula would be tested.
For aerosol sunscreens, this creates an idealised 'best-case scenario' that may not reflect how consumers typically apply them outdoors.
This means that the amount of product used in testing is unlikely to reflect the amount of sunscreen formulation that actually reaches the skin during real-world use.
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Skin coverage from aerosol spray sunscreens
Aerosol spray sunscreens can vary widely in how much actual sunscreen they deliver, because each spray also releases propellant gas. In a 2020 report by Queensland University of Technology, with advice and assistance from Cancer Council Victoria and ARPANSA (Australian Radiation Protection and Nuclear Safety Agency), nine aerosol sunscreens were tested and found to contain between 27% and 83% propellant.
Similarly, this impacts for how long you should be spraying yourself, as this varies significantly by product - with some brands requiring four seconds to get the recommended amount of sunscreen on one limb, and others needing 14 seconds.
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Studies also show that wind speed can affect ‘overspray’, this is when fine spray droplets drift through the air and land on nearby surfaces instead of where you intended to spray.
In a light breeze, more than a third of sunscreen can be lost to the air and miss the skin; in moderate wind, that figure can rise dramatically. Given that people may be reapplying their sunscreen throughout the day while outdoors, this could be concerning.
To achieve the SPF stated on the label, you may need to spray for significantly longer, making these 'convenient' sprays potentially more expensive and less effective than expected.
The Australian researchers looking at aerosol sprays found that, depending on the brand, most contained enough sunscreen for two to three whole-body applications before the can ran empty.
If you're reapplying regularly (as is recommended), you could end up getting through one can of sunscreen per day on your holiday, which could see costs adding up.
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Are spray sunscreens bad for the environment?
There’s also the sustainability factor.
Many aerosol sunscreen cans use propellants, some of which are volatile organic compounds (VOCs) that can contribute to local air pollution. Also, you'll need to check if your local authority will collect empty aerosols with other recycling - check the Recycle Now site.
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How should you apply spray sunscreen?
If you choose to use an aerosol sunscreen, you should:
- Shake the can vigorously. Active ingredients separate in pressurised cans between uses. Shake for five to 10 seconds to ensure a uniform mix.
- Hold the nozzle close. Position the nozzle 10 to 15cm away from your skin.
- Spray generously and continuously. Apply in a well-ventilated area to avoid inhalation, but stay out of heavy wind, which blows away coverage. Your skin must look visibly wet, shiny or glistening, and you should see a distinct layer of damp product sitting on top of the skin.
- Never spray directly onto your face. Spray a generous pool into your hands first, then spread it evenly onto your face, ears and neck. This prevents painful eye irritation and accidental inhalation.
- Always rub it in. Rubbing distributes the active ingredients uniformly and fills in invisible gaps.
If you're using a lotion or pump spray (non-aerosol), remember to:
- Apply one teaspoon for each body part that is exposed to the sun around 15-30 minutes before you head outdoors, and rub in well.
SPF application guide:
- Face, neck and ears – 1 teaspoon.
- Each arm and hand – 1 teaspoon.
- Front of torso (chest and abdomen) – 1 teaspoon.
- Back of torso and shoulders – 1 teaspoon.
- Each leg and foot – 2 teaspoons.
- Reapply every two hours, and sooner if you go swimming, are active, or if you sweat a lot.
Don't just rely on sunscreen to protect you. Make use of hats, clothing and shade where possible to protect yourself, especially in the middle of the day when the sun is at its strongest.
