Sydney Sweeney's doe eyes may be thanks to her genes, but her long, thick lashes get a little help from this Amazon beauty buy -- which is currently on sale for 25% off ahead of National Lash Day.

"I saw this TikTok of this girl who uses this eyelash serum, and I ordered it, and my eyelashes started growing like crazy," the "White Lotus" starlet told Refinery29 in 2021.

"It's RapidLash; I use it every day. Everyone has said something. I don't ever tell anyone. My makeup artist, Melissa Hernandez, was like, 'Sydney, your eyelashes are longer.' Then Donni, my makeup artist for "Euphoria" was like, 'We don't even need to put eyelashes on you anymore.'"

Made with polypeptides, biotin, panthenol, amino acids and soybean oil, the formula seals in moisture and protects brittle lashes. And along with racking up thousands of five-star ratings on Amazon, it's earned rave reviews on TikTok and from industry experts, too.

"RapidLash EyeLash Enhancing Serum has become my favorite over-the-counter lash enhancement serum," board-certified dermatologist Dr. Lian Mack tells Page Six Style.

"Apply to the upper lid margin (where the lash connects to the skin), starting from the inside out. Having tested this product personally, I had visibly longer and healthier-looking lashes in just over two months! The formulation applies with ease and no irritation."

Mack tells us that "the length of your eyelashes is for the most part genetically predetermined," but adds, "biotin (a water-soluble B-based vitamin,) amino acids and polypeptides improve keratin production of the hair, promoting the growth of thicker, stronger lashes."

Ahead of National Lash Day on Feb. 19, why not pick up a tube to try for yourself? After all, this deal is bound to be gone in the blink of an eye.