A 2025 Study Scores White Cast: How Much Zinc Before Mineral SPF Looks Ashy
A 2025 PLoS One study built the first standardized white-cast scale, giving you a concrete zinc-oxide percentage rule for picking a mineral SPF that won't leave you ashy.
A PLoS One study published August 26, 2025 created the first standardized white-cast scoring method for zinc oxide mineral sunscreens across skin tones, grading 0% ZnO as no white cast, 5% as reasonable, 10% as the threshold, and 20-30% as unacceptable, while finding cast manifests differently by skin tone.
The study's authors frame standardized white-cast scoring as a way to improve user compliance, reasoning that a formula people will actually wear protects better than a high-zinc one they abandon over cosmetic appearance.
Questions we get a lot
How much zinc oxide causes a white cast?
The 2025 PLoS One study graded 0% zinc oxide as no white cast, 5% as reasonable, 10% as the threshold, and 20-30% as unacceptable. So formulas in the higher ZnO range are the most likely to look ashy.
Does white cast look the same on everyone?
No. The study found that white cast manifests differently depending on skin tone, which is part of why a standardized scoring method across diverse tones was needed. The same formula can read very differently on deeper skin.
Why does white cast matter for sun protection?
Because if a sunscreen looks ashy, people are less likely to wear it consistently, undermining its protection. The study explicitly links standardized white-cast scoring to improving user compliance across diverse skin tones.
r/SkincareAddiction: 'Every mineral sunscreen I try makes me look gray. Is there a zinc oxide percentage I should stay under to avoid the white cast?'