Olfactophilia (also known as osmolagnia, osphresiolagnia, and ozolagnia) is a paraphilia where an individual derives sexual pleasure from smells and odours. Given the large body of research on olfaction, it is unsurprising that in some cases there should be an association with sexual behavior.
The erotic focus is most likely to relate to body odors of a sexual partner, including genital odors. One of my favourite papers examining sex and smell was a 1999 paper by Dr. Alan Hirsch and Dr. Jason Gruss published in the Journal of Neurological and Orthopaedic Medicine and Surgery. As they note in the introduction to their study, sex and smell have a long association:
“Historically, certain smells have been considered aphrodisiacs, a subject of much folklore and pseudoscience. In the volcanic remnants of Pompeii, perfume jars were preserved in the chambers designed for sexual relations. Ancient Egyptians bathed with essential oils in preparation for assignations; Sumarians seduced their women with perfumes. A relationship between smell and sexual attraction is emphasized in traditional Chinese rituals, and virtually all cultures have used perfume in their marriage rites. In mythology, rose petals symbolized scent, and the word ‘deflowering’ describes the initial act of sex…
Dramatic literature abounds with sly references to nasal size as symbolic of phallic size, as in the famous play Cyrano De Bergerac…Psychoanalysis has made much of these associations. Fliess, in his concept of the phallic nose, formally described an underlying link between the nose and the phallus. Jungian psychology also connects odors and sex”.
In contemporary society, perfumes for women and colognes for men are marketed aggressively because it is a multi-billion pound business and are advertised in a way that suggests sexual success for those who use such fragrances. Hirsch and Gruss argue that:
“The prominent connection between odors and sex among diverse historical periods and cultures implies a high level of evolutionary importance. Freud suggested that odors are such strong inducers of sexual feelings that repression of smell sensations is necessary to civilization.
Anatomy bears out the link between smells and sex: the area of the brain through which we experience smells, the olfactory lobe, is part of the limbic system, the emotional brain, the area through which sexual thoughts and desires are derived. Brill  suggests that people kiss to get their noses close together, so that they can smell each other (the Eskimo kiss). Or possibly they kiss to get their mouths together so they can taste each other since most of what we call taste is dependent upon olfaction”.
One of the research areas that I have published a couple of papers with Dr. Mark Sergeant (see ‘Further reading’ below) in is on the area of pheromones (i.e., chemical substances “produced and released into the environment by an animal, especially a mammal or an insect, affecting the behaviour or physiology of others of its species”). Pheromones are known to exist across the animal kingdom from insects to primates (possibly including humans but most robust scientific studies have shown the evidence is relatively weak, and if pheromones do exist in humans the effects are likely to be very subtle). As Hirsch and Gruss note:
“Inside the human brain, near the top of the nose is an anatomical feature that gives us reason to believe that human pheromones exist: the vomeronasal organ. Its function is unknown, but in subhuman primates, this is the area where pheromones act to increase the chance of procreation…
When we exercise, we sweat through endocrine glands. But when we are embarrassed or sexually excited, we sweat through apocrine glands that release high-density steroids under the arms and around the genitalia; their role is unknown. In subhuman primates, the same apocrine glands release pheromones”.
Other research by Dr. Hirsch has shown evidence that links smell with sexual response. For instance, in one of his studies, 17% of patients that had “olfactory deficits” had developed some kind of sexual dysfunction.