Testing How the Application Order of Sunscreen and Makeup Primer Affects UV Protection

Using a UV lamp and a UV meter, he measured the UV reduction rate (an approximate SPF value) of sunscreens and primers applied to clear film, both on their own and layered.

Main combinations tested:

• Non-chemical with non-chemical: Ceraneige UV Cream (sunscreen) × Ceraneige High-End Cover UV Base (primer)
• High-SPF sunscreen × low-SPF primer: ANESSA UV Gel × Clé de Peau Beauté Voile Correcteur n
• High-SPF sunscreen × primer with no SPF listed: Skin Aqua Hyaluronic Serum UV × NARS Soft Matte Primer
• Drugstore products with different powder properties: by365 Powdery UV Cream × Sana Nameraka Honpo Skincare UV Base
• Zinc oxide-free with zinc oxide-free: Bioré UV Mizuhada Kioku UV × Curél Foundation Barrier Base
• Highest-rated UV with highest-rated UV: Bioré UV Athlizm × Chacott Lasting Base

• No cases of reduced UV protection: In every combination, layering sunscreen and primer never lowered protection below that of the original product.
• Even primers with no SPF listed improved protection: Even when a primer with no SPF listed was layered over sunscreen, overall UV-blocking performance improved significantly, likely because the film became more even, among other reasons.
• Differences by application order: In most combinations, "sunscreen first, primer second" provided higher protection, but depending on how well the formulations worked together, there were also cases where the reverse order performed better.
• The effect isn't simply additive: Layering increases protection, but SPF values don't simply add up.

• "Sunscreen first" is fine as a rule: There's no need to worry about reduced UV protection, and considering foundation adhesion and the finish of your makeup, the conventional order of "skincare → sunscreen → primer → foundation" is still recommended.
• When applying primer, don't rub it in hard; instead, gently press it on (stamping application) to prevent unevenness and help maintain strong UV protection.