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Welcome to I'm Obsessed, a daily video series with Angelique Serrano, InStyle's beauty director. Check back every weekday to learn more about the beauty products and tools she can't get enough of.

Don't underestimate the power of this tiny serum. Though Guerlain's Radiance in a Flash may look unassuming, the product delivers major results for your complexion, just as its title suggests. When worn underneath foundation or tinted moisturizer, the shimmer-infused gel imparts an instant Valencia filter effect on your skin, but can also be used over makeup for a mid-day refresh. The rest of the InStyle team was so impressed by the product, immediately after a meeting, we all went and picked up bottles of our own. Hit play on the above video to find out how Serrano likes to use it, and all about the frenzy it caused over at InStyle HQ.

Shop it: $30; sephora.com.

Watch the video above to learn why Serrano loves it—and visit instyle.com/videos for more of our favorites.