The smells awaken in us a flood of feelings that can really relax us and lower our stress levels. This is indicated by a study conducted at Columbia University and published in the Journal of Personality and Social Psychology. This study indicated that your couple's smell helped to reduce stress and, on the contrary, the smell of a stranger made us nervous.
The study was conducted with heterosexual couples, although in the future the aim is to increase the diversity of the couples to make the experiment more rigorous. In this study women were chosen because they're considered to have a sense of smell normally finer than men.
The experiment consisted of giving men new shirts to be impregnated with their smell without contaminating them with tobacco or deodorant odors. During the study it was observed that many people sleep in their couple's shirt or sleep on their couple's side of the bed when they aren't there.
Women were asked to recognise the smell but not to indicate whether it belonged to their couple. After smelling the shirts, they were given a saliva test to measure cortisol levels. It was detected that when they smelled their couple's shirt, without knowing it, they were reducing the level of cortisol, the hormone that alerts us to a danger.