• Andrés Martínez, science journalist

    Body odour, more than just bothersome

    20 Apr

    Our bodies smell. As do the bodies of all the animals on earth. The bacteria in our skin break down our sweat and create our personalized odour. The emotions and sex appeal also have olfactory reflexes. Is the rise of personal hygiene causing this means of communication to disappear?


    The skin acts to keep the body cool and to do this it secretes sweat, which, when it evaporates, absorbs heat and maintains an ideal body temperature. But it may come as a surprise to know that sweat itself is not responsible for body odour (BO). That dubious honour belongs, in fact, to the bacteria that naturally colonize our skin. The odourless, oily and protein-rich liquid secreted by the sweat glands is a source of nutrients for skin bacteria. Bacterial metabolism releases volatile organic substances that produce odour.

    Microbial flora proliferates in parts of the body where there are many sweat and sebaceous (fat-secreting) glands and where moisture tends to be retained, whether in body folds, clothing or footwear. Not surprisingly, the armpits, groin and feet are the smelliest parts of our body.


    Olfactory communication

    Body odour, however, far from being a problem to be remedied or masked, fulfils certain functions, some long known ones linked to sexual attraction and others revealed more recently. In recent decades, researchers have discovered that our body odour is affected not only by our level of physical activity, but also by genetics, age, emotional state and food intake, and also that body odour plays a social and sexual communication function. Science has confirmed what was already popular lore.

    We now know that, when we are stressed or excited, the glands in the armpits give off a distinctive and perceptible odour. Our BO is thus a kind of messenger for our emotions, as has been confirmed for fear, for example. Some of the substances involved are secreted from puberty and some are derived from testosterone, a sex hormone.


    We capture 10,000 smells

    The fact that some people are more sensitive to body odour than others seems to be determined by genetic makeup. Thus, possessing a certain gene intact makes a person particularly sensitive to one of the components of sweat, isovaleric acid.

    But distinctive perceptions of BO are not explained exclusively by this gene. The fact that humans have hundreds of olfactory receptors that can distinguish up to 10,000 smells may well explain why an odour that is pleasing for some is unbearable for others.


    Seductive perfumes and selective deodorants

    Many studies seek to discover how, through certain substances called pheromones – whose activity has been confirmed in relations between animals – body odour affects personal attractiveness and sex appeal. The perfume industry is naturally interested in knowing about substances that potentially increase the attractiveness of a perfume.

    The cosmetics and textile industries are interested in developing anti-bacterial and anti-perspirant additives to include in deodorants and fabrics, with the idea being to inhibit odour-causing bacteria without affecting beneficial bacteria, or to reduce the secretions that produce bad smells. Neutralizing the main culprits, called coryneform bacteria, is the main objective.


    The hygiene revolution

    Humanity has always lived with body smells and this explains the secular use of incense in churches and the use of precious perfumes and essences. Until the 19th century, bathing was a habit of the wealthy, although only practiced sporadically. Perfumes, far from fulfilling a purely aesthetic function, were used to conceal personal smells. The common people, especially those in the cities, lived in unhealthy surroundings that would be intolerable to us today.

    Hygiene began to take off thanks to advances in public health and, above all, thanks to the universal use of sanitation and running water from the 20th century, coupled with great growth in the industrial manufacture of soaps, which had already begun in the previous century.

    The habit of a daily shower and skin care, which now seems so typical, was only introduced relatively recently in advanced countries. As a result, our body odour, nowadays kept to an absolute minimum, has shifted from being a significant marker of our personality to being the subject of scientific studies.



    International Journal of Cosmetic Science

    History of Hygiene