Within 20 seconds of encountering a beautiful woman, men have been shown to have a surge of two hormones: testosterone and cortisol. This makes good sense, evolutionarily speaking. As I describe in BLONDES, hormones mirror the subconscious mind. Testosterone promotes assertiveness and reflects increased sexual desire. Cortisol focuses motivation. Women are the choosier of the sexes, which means — generally, of course — that the onus is on men to flaunt and flatter or take other action to attract the woman.

But what do women do when they see an attractive man?

The same thing. Far from being passive observers, women also experience a hormonal riot within seconds of seeing a hot guy. This is true even if the man is an actor in a film, as indicated in a new study led by neuroscientist Hassan Lopez at Skidmore College. Lopez and his team showed 120 women one of four 20-minute videos, each with a different scenario: 1.) an attractive man courting a woman (a clip from The Notebook starring Ryan Gosling) exhibiting a dominant social presence, risk-taking, kindness to children, faithfulness, confidence, and humor 2.) a nature documentary about caves; 3.) an unattractive older man (Jack Nicholson) courting a woman 4.) an attractive woman (Cameron Diaz) with no man present. Saliva samples were taken right before and after each viewing.

Of all four groups, only the women watching the hot, desirable, “high mate value” guy trying to seduce a woman had a surge of testosterone and cortisol. The higher the hormones, the stronger the romantic/sexual interest the women reported. (Interestingly, women on birth control pills only experienced a cortisol surge, not testosterone, apparently because the pill suppresses the hormone. Naturally-cycling women also reported a greater willingness to engage in sexual activity and enter a relationship with the attractive man. This may be due to stronger hormonal surges in women who aren’t on the Pill or the fact that more Pill-takers are already taken.)

The study reminds us that hormones help both sexes focus and flirt more effectively, and a surge at the sight of an attractive prospect may change our moods in an instant. But what threshold must be met to trigger such a surge? Do women with higher baseline testosterone and cortisol levels respond faster and get turned on easier? Are high testosterone men more effective in raising women’s hormones? Could taking the Pill really decrease your natural attraction to handsome strangers? And when two people mutually elevate each other’s hormones within seconds, is that considered love at first sight — or just lust?