Vitamin K

In the world of skincare vitamins, you've probably heard of—and probably used or are currently using—vitamins A, C, and E. But if you work your way further down the alphabet, there's another vitamin that may have some topical benefits, too. We're talking about vitamin K, a vitamin that plays an important role in several different bodily functions. And while it's typically thought of as a more systemic vitamin, there's a good amount of topical products out there that tout it, too. So, does it perform as well on the skin as it does inside our bodies? 

What is Vitamin K?

Just as its name suggests, vitamin K is a fat-soluble vitamin, which is found in food and synthesized in the large intestine. It plays an important role in many bodily functions, including blood clotting, blood calcium regulation, and bone health, says Chang. (Fun fact: That's why it's called vitamin K because the German word for coagulation is koagulation). It's also known as phytonadione.

While vitamin K is well-known for its many systemic benefits, "the mechanism by which vitamin K works in the skin is still unclear," says Chang, who adds that whether or not it even works effectively as a skincare ingredient is up for debate. She notes that there have been many different studies researching its topical benefits, though is quick to note that further research is needed before coming to any conclusive takeaways. The bottom line? Take these purported benefits with a grain of salt, and know that the science backing vitamin K is nowhere near as strong as that of other vitamins. Still, here's what it potentially can do:

• Promotes wound healing: "Vitamin K may improve wound healing by increasing wound contraction and helping in the formation of collagen and blood vessels," says Chang. (FYI, wound contraction is essentially a healing response your body has that determines how much skin has been damaged and needs repair).
• May have some antioxidant properties: Russak says Vitamin K has, "redox properties," referring to the skin's ability to detoxify reactive oxygen species (also known as ROS) that are formed when we're exposed to things such as UV rays and pollution.
• Helps fade under-eye circles: Most of the skincare products touting vitamin K are eye creams that claim to brighten the under-eye area. In theory, this should be due to the effects the vitamin has on the blood clotting process, and how it affects the blood that pools in the tiny vessels underneath the eye. However, our experts were split on the legitimacy of this benefit. While Russak feels that, "it's a great option for people with dark circles and pigment under their eyes," Chang is a bit more skeptical. In a 2015 study, participants who used pads containing vitamin K and caffeine in an emu oil base had an improved appearance of wrinkles and dark circles.1 However, Chang is quick to point out that the study had limitations. "It's unclear whether the improvement in dark circles was due to vitamin K or from the caffeine and emu oil in this study," she says.
• Helps lessen the appearance of dark spots: Doctors often turn to Vitamin K creams for patients who need help reducing swelling or bruising, so it stands to reason that the ingredient has been shown to reduce the appearance of dark spots.
• Improves the look of stretch marks: Because of its ability to increase elasticity, vitamin K can make a stretch mark prone area appear a bit lighter and brighter.
• Non-irritating: Vitamin K is non-irritating and safe for use with all skin types, even sensitive.

• Available over-the-counter: Unlike some super skincare ingredients, vitamin K products are available in most beauty and drugstores.
• Helps combat wrinkles: Similarly to the under-eye circle study, an older study from 2004 found vitamin K to be beneficial in minimizing dark circles and wrinkles... but in this case, the vitamin K was paired with retinol, as well as vitamins C and E.2

Side Effects of Vitamin K

Here's the thing, though: Although the jury is still somewhat out, vitamin K has no known side effects. "Unless someone has an actual allergy to it, it's safe for all skin types," says Russak. Oh, and one other contraindication—because of the effect it can have on blood clotting, anyone with a risk of blood clots should consult with their physician before using vitamin K, she advises. The bottom line: If you want to give it a try and see if it can help knock out dark circles, there's no real harm in doing so.

How to Use and Apply Vitamin K

As a general rule of thumb, you can go ahead and use it once or even twice daily, given that it's most often found in eye creams. For the best results, search for it in formulas where it's paired with other brightening ingredients—think caffeine, arnica—or even with retinol, which may help to improve the penetration of the vitamin K, according to Russak.