You’ve probably been told to calm down and “take a deep breath” at some point in your life. Maybe you rolled your eyes at the advice, but science shows that this trick really can help you relax.

First, some breathing basics: When you inhale, you trigger your sympathetic nervous system to kick in—the one that’s wired to boost your heart rate and blood pressure, says Bill Hartman, P.T., C.S.C.S., Men’s Health’s sports medicine advisor.

But on an exhale, you kick-start your parasympathetic nervous system, which lowers your heart rate and BP, he says.

So when you’re stressed, slowing down your breathing and focusing on that exhale sends your body into a parasympathetic resting stage, helping you unwind, says Hartman.

Deep breathing also calms you down because it forces you to redirect your attention to your body—not the stuff around you that’s stressing you out, says Christina Vestergaard, M.D., M.P.H., a pulmonologist at Massachusetts General Hospital.

Feeling a little tense? Try this “4-7-8” breathing exercise from Andrew Weil, M.D., founder and director of the Arizona Center for Integrative Medicine: Close your mouth and inhale through your nose for four counts. Hold your breath for seven counts. Then, exhale while mentally counting to eight. Repeat the cycle three more times. (That’ll take you less than 2 minutes.)

Here’s why this works: When you breathe in through your nose, it helps enhance your breath’s calming effects because sensory receptors for the parasympathetic response are located in your nostrils and sinuses, Hartman says.

Holding in your breath increases carbon dioxide in your blood stream, which relaxes your blood vessels and lowers your blood pressure.

In fact, you might find that you naturally hold your breath sometimes, like when you’re watching TV at night after a hard day’s work. That could be your brain’s way of helping you de-stress.

So give the 4-7-8 technique a shot: It could be like an all-natural chill pill for your body.