(A) follicular phase (B) luteal phase

By now, you probably know I love to report on various methods that indicate where you are in your menstrual cycle, such as doing the “dipstick” test, using easy tools, monitoring mood and energy changes and trying a forthcoming fitness tracker.

That’s because knowing where you are in your cycle enables you to predict what your day will be like:

For instance, if you’re in the first half of your cycle (the two weeks leading up to and including ovulation), you’ll know that estrogen is rising, which means you’re likely to have more energy, a brighter mood, better sleep and more optimism. You’ll know you’ll build more muscle when you do strength-building exercise and will be more flirtatious around cuties that you find attractive. And, you’ll find it easy to be inspired and come up with creative ideas.

If you’re in the second half of your cycle (the two weeks after ovulation leading up to your next period), you’ll know that estrogen dips twice and sedating progesterone dominates, so you’ll likely be battling a bit of fatigue and be more prone to sad or irritating moments, good sleep could be harder to come by and you’ll be facing issues with a more realistic or possibly pessimistic mindset. You’ll also know you burn up to 30% more fat when you do aerobic exercise and be more introverted and serious. And, you’ll find it more of a challenge to muster inspiration and churn out creative ideas.

So, you can see why knowing where you are in your cycle can make a dramatic difference in what to expect.

That’s why I’m intrigued to discover a new study in the Journal of Traditional and Complementary Medicine that reveals you can tell if you’re in the first half or second half of your cycle by looking at your tongue.

Turns out, the color of your tongue changes depending on which stage of your cycle you’re in: The tip of your tongue is redder and brighter during the second half of your cycle (the luteal phase) than the first half (the follicular phase).

The reason? The researchers theorize it’s because progesterone is triggering a slightly higher body temperature, which causes more blood flow to reach the tip of your tongue, changing its color.

The researchers go on to point out that you’ll also notice a yellow coating on the middle of your tongue during the second half of your cycle–and that’s likely due to a higher amount of sulfur compounds (odor-causing molecules), which are yellowish in color and more prevalent during this cycle phase.