updownsignWhen you think of your fluctuating hormone levels, you might assume that how far and when they rise or fall is dependent upon what’s going on inside your own body. But, believe it or not, there are certain instances when you can “catch” someone else’s hormones, resulting in a change in how much of a hormone your body produces.

Here are two times when it can happen with your testosterone. Even though your testosterone tends to get churned out at a stable low rate throughout your cycle and rise briefly during ovulation (see chart), your testosterone level can suddenly change when:

1. You kiss a man: If you French kiss a man (a kiss using your tongue), he’s actually passing a small dose of testosterone to you via hormones in his saliva, says biological anthropologist Helen Fisher, Ph.D. This hormone-spiked saliva then raises your own testosterone level temporarily. Fisher theorizes that one reason men might enjoy sloppy kisses is because testosterone revs the female sex drive, so they nonconsciously use their saliva as a way to boost your testosterone and, with it, your libido.

2. You’re near an ovulating woman: According to a 2013 study published in the journal Evolution & Human Behavior, being in close proximity to a woman who’s in the fertile phase of her cycle–which is when her testosterone level rises–prompts your body to churn out more testosterone, too, regardless of where you are in your cycle.

It also works the other way: Being physically close to a woman who’s in a non-fertile phase of her cycle–when her testosterone is lower–prompts your body to reduce its testosterone level.

Why do our bodies make this hormonal change based on where other women are they are in their cycle? The study authors speculate that it may be because females evolved to send out signals during ovulation that let others know they’re fertile–and this, in turn, touches off a competition with nearby women for the best mates with whom to procreate. So, our testosterone levels shoot up as a way to boost our confidence and assertiveness, making us better able to muscle our romantic rivals out of the way.

On the flipside, when women aren’t fertile, we evolved to be social and supportive of one another. And a lower level of testosterone would encourage more cooperation among us.

So, what can you do with this information? If you ever need a quick spike in confidence, assertiveness, competitiveness, physical stamina, libido or mood, you may want to try to “catch” more testosterone from a wet kiss with a man or by standing near an ovulating woman. This hormone is known to boost all these traits, giving you extra hormone-fueled oomph for an important job interview, big pitch, athletic competition or hot date.