Researchers had more than 8,500 women look at pictures of men’s faces, which were either clean shaven, bearded, or stubbled. Then the women rated each image for sexual attractiveness.

The women rated men with any kind of facial hair—beards or stubble—as 15 to 20 percent more attractive than guys who were clean shaven.

That’s because facial hair is a sign of masculinity, says study author Dr. Danielle Sulikowski, professor of psychology at Charles Sturt University in Australia.

Related: The MH Style Team’s #1 Grooming Rule For Men Over 30

It comes down to natural instincts: Facial hair makes you seem like a strong, dominant guy, which makes you a better mate choice from an evolutionary perspective, Sulikowski says.

But if you really want to catch her eye, stick with stubble—women rated it as the hottest type of facial hair.

That could be because stubble is a happy medium, says Sulikowski. The facial hair will turn her on, but she still gets to see your face underneath it.

Related: 5 Rules For Styling Facial Hair To Compliment Your Face 

To rock the perfect stubble, follow these steps from the Men’s Health fashion editor:

1. Use an adjustable beard trimmer with a built-in guard.
2. Start by removing any hair that grows too far out of bounds. Without using a guard, turn your trimmer so the blades face down. Shave a curved line around your neck, hitting just above your Adam’s apple. Shave off all the hair that grows below that line. Try to fade your facial hair as much as possible. Working slowly will help you avoid harsh lines.
3. If your facial hair grows high up on your cheeks, shave or trim the hair there, making sure the start of your stubble hits just below your cheekbones, parallel to your jawline.
4. To groom the hair above your lip, align the trimmer with the top of your lip and trim your mustache so that it lies a millimetre or two above the top of your lip.
5. Turn your trimmer so the blades face up and put on your desired guard. (If you’re unsure, start with 1/4 inch for darker hair, or 1/2 inch for lighter hair.) Trim your remaining facial hair to that length. When you’re trimming your sideburns, stop trimming where your facial hair meets your hairline, which is normally around your mid-ear.
6. Run your fingers over your stubble to check for consistency, making another pass with the trimmer until your stubble is even.

Related: How To fix A Dodgy Beard Trim