For me, eyebrow serum is one of those things I can’t imagine not having in my beauty routine. However, life gets busy and there are times where I don’t have one in my rotation, and the tails of my brows just sort of disappear, which is the worst reminder that I’ve been neglecting them. This Probiotic XEyebrow Enhancer from Dr. Lili Fan, a biochemist, microbiologist and practicing ophthalmologist, is just what the doctor ordered to bring sparse brows back to life. Here’s the inside scoop on what makes it so good. (You can try it yourself if you’re one of the lucky ones to snag this week’s BeautyPass Free Gift Friday. Click here to sign up for BeautyPass if you haven’t already).

The Benefits:

When it comes to eyebrow serums, most of them function similarly in the sense that they are a clear serum that you apply on your brows to enhance their appearance. So what sets one apart from the other? The key ingredients. This one contains an exclusive peptide complex that Dr. Fan patented, which includes myristoyl pentapeptide-17 and five other types of peptides, which make the brows appear longer, denser and thicker in just four weeks (though for some people it can take up to three months to see full results).

The addition of folic acid and biotin—two ingredients (both B vitamins) you see in most hair-growth products and supplements—promote healthy hair growth. You may have also seen castor oil in eyebrow serums before, too, as it’s rich in oleic acid, which also helps to keep hair follicles healthy and reduce hair loss. Coconut oil is another key ingredient that lends shine and softness so the brows are more manageable and less likely to fall out.

Probiotics play a role, too, and Dr. Fan’s proprietary formulations take a different approach to the trending skin-care ingredient, using rice as a starting point to obtain the pharmaceutical-grade probiotic (lactobacillus acidophilus). This helps ensure that there is no potential allergic reaction, which Dr. Fan says normally occurs with probiotics that are derived from dairy instead. Utilizing her scientific background, she’s also able to select and extract only the active compound of the derived probiotic, rather than the entire extract, which she says is standard.

Key Ingredients:

Folic acid, biotin, castor oil, coconut oil and the brand’s exclusive peptide complex

How to Use It:

Just brush the clear serum onto clean brows in the morning and at night and give it a second to dry. It’s as easy as that! I like to keep mine next to my toothbrush, too, so I never forget it.

The Bottom Line:

This serum is supercharged with hair-growth actives that make thicker, youthful-looking brows easier than ever to achieve. And it’s essentially foolproof!

Price/Where to Buy:

$65, drlilifan.com