Passion + Attraction = Attachment
It’s not your eyes that make you fall for someone—it’s the chemicals in your brain and glands. This cascade of hormones and neurotransmitters creates euphoria and fosters bonding in three basic phases.
Testosterone + Estrogen
Lust is visceral and can be instantaneous. Testosterone and estrogen, the hormones produced in the testes and ovaries and in small amounts in adrenal glands, kick out their amorous signals even before your mind registers a single fact about the object of your desire.
Thank your adrenal glands for the norepinephrine that makes your heart pound. The hormone is linked to adrenaline, which helps increase circulation, crucial for arousal.
Once your body says, “Hello, sexy,” your brain produces this neurotransmitter, which increases libido and euphoria. It’s also tied to addiction: That love-drunk feeling will keep you coming back for more.
Lovers spend 95% of the day thinking about the object of their passion, according to one study. Scientists liken that level of obsessiveness to OCD.
Researchers say new couples have lower levels of this neurotransmitter, which is largely produced in your gut. This may be what causes focused attention on the object of your desire.
Related: How To Strengthen Your Heart Chakra 
The brain makes this empathy-inducing hormone after orgasm. Nonsexual skin-to-skin contact fuels it, too, helping you feel connected after the early chemistry wanes.
20 Seconds–The amount of time you should hold a hug to trigger a burst of oxytocin.
In prairie voles, this hormone causes a desire for monogamy with a partner after mating. Combined with oxytocin and prolactin, it’s also why guys experience postcoital fatigue.