Researchers have found that a factor that determines our sexual orientation is our reaction to our partner's smell.

Sexual orientation emerges in people in early adolescence, when they have mostly not yet had any intimate experiences. For years, there has been a dispute as to whether the development of our sexual preferences is influenced by biological, psychological, social factors or all of them at the same time.

One of the opinions put forward is that sexual orientation is determined by the brain. Numerous studies have shown that the brains of men and women differ in terms of structure and function. The male ones, for example, are more asymmetrical, with the right hemisphere larger than the left. Researchers therefore began to wonder whether there are differences between the brains of people of the same sex but different sexual orientation.

Studies were carried out that suggested that the third hypothalamic nucleus in gay men is significantly smaller than in heterosexual men. There is also a difference in the great spiracle, which is 18% larger in heterosexual men than in women and 35% larger than in gay men.

Breakthrough discovery

Experiments carried out in a number of countries have sought to prove what causes this and not that sexual orientation in humans. Swedish scientists at the Karolinska Institute in Stockholm, finally investigated the anatomy of the brain in the context of sexuality.

They noted that gay men's brains resemble those of heterosexual women, and lesbians' brains resemble those of heterosexual men. Based on the results of their research, they also reported that they had found two human pheromones responsible for sexual orientation: Androstadienone, found in male sweat, and Estratetraenol, present in female urine.

Androstadienone (a derivative of testosterone) was shown to strongly activate the female brain. The same was true for Estratetraenol, a derivative of the female sex hormones, oestrogen. This compound strongly stimulated the brains of heterosexual men.

So the Swedish researchers decided to go one step further and test whether the effect of pheromones depends only on gender or also on sexual orientation.

They conducted an experiment in which they invited 36 people - 12 heterosexual women and 24 men, half heterosexual and half homosexual. Initially, they were given samples of common scents, such as lavender or cedar, to smell. Tests using magnetic resonance imaging and computed tomography showed that the centres associated with the sense of smell were stimulated in their brains.