Love has three phases: lust, attraction, and attachment.
In phase one (lust), the brain produces testosterone and estrogen, driving individuals to seek sexual gratification with a given person.
In phase two (attraction), the brain produces more dopamine and norepinephrine, but less serotonin, than usual. This causes individuals to feel euphoric around their loved one, but also leads to intense infatuation with them. Phase two usually lasts between six months and three years.
In phase three (attachment), individuals’ attraction goes down. The brain instead produces more oxytocin and vasopressin, prompting individuals to bond with and nurture their partner. While lust and attraction are exclusive to sexual and romantic interests, attachment happens just as it does for others in one’s life, such as close friends and family members.