5. THE MHC
The Major Histocompatibility Complex (HMC) is a set of cell surface molecules encoded by a large gene family which controls a major part of the immune system in all vertebrates. In humans, the MHC is also called the human leukocyte antigen (HLA). Several studies have reported a tendency for humans to prefer MHC-dissimilar mates.
MHC is exuded in our bodies through sweat, saliva and body odour. It is believed that the more you differ in MHC levels the more attracted you would be to that person.
6. PHEROMONES
Pheromones are chemicals released by an organism into its environment enabling it to communicate with other members of its own species. They are believed to play a part in human sexual attraction.
When you fall in love with someone, you tend to get accustomed to their smell.
S.O.Z