Euphemistically speaking, human olfaction is dull. In fact, olfaction barely has any role in our life, except in feeding. Is it so?
Most mammals have on the top of their mouth, where the vomer bone is located, an olfactory formation called the Jacobson organ. This organ detects all the pheromones in the female's urine, which inform on her hormonal load and based on this, the male takes action or not. I'm sure that you saw in many documentaries the stupid grimaces made by lions or male bisons at a certain part of the females' body. They are just sniffing urine with their Jacobsons, in a behavior called flegmen, and this is not a gesture denoting sickness.
Even if the human Jacobson is not visible, many researchers say it reacts to human sweat. Maybe that's why women are turned on by the macho style, handling a pick-hammer, sweating in the sunlight. The scent of the man sweat can regulate the woman menstruation and favor fertilization. A woman's brain can detect chemicals in the man's sweat in only 3 seconds when they first date.
The woman's nose can detect also perfumes associated with male scent, like musk, in concentrations below those that trigger conscious sensations. That's why perfumers put in perfumes pheromones found in nature, like musk or civet (more recently, their synthetic variant).
In the male scent, the female brain can detect information on man's immune system: if it's stronger than hers or complementary, she will find the man attractive and endowed with a mysterious magnetism.
Swiss researchers at the University of Berna made the next test: they put 6 men to wear cotton T-shirts for two consecutive nights, in a neutral environment. The shirts were given to be sniffed and classified by 100 women. The results: the more different man's immune genes were from those of the woman, the more pleasant the woman found the man's scent. But women using contraceptive pills showed no preference of this type.
The researchers explained this through the fact that fertile women looked for a partner that could boost the immunity of a possible child.
After all, women enjoy wearing the T-shirts of their lovers. Why should this be? Not to mention that the erotic memories include the scent or perfume of the partner (including ex-partners)...