: Because the brain is so highly attuned to this information, a "bad" first kiss can actually stop a promising relationship in its tracks by signaling biological incompatibility. 2. The Brain’s "Chemical Cocktail"
: The exchange of saliva allows us to subconsciously pick up on a partner's immune system markers (MHC genes). Humans are often attracted to those with different immune system genes, which can lead to healthier offspring. : Because the brain is so highly attuned
: Saliva contains hormones like testosterone, which can increase arousal and signal sexual readiness. : Because the brain is so highly attuned