Understand armpits biology and the use of deodorants

  • May 4, 2023
  • 4 minutes of read time

Understand armpits biology and the use of deodorants

Body care

On a daily basis, we sweat and evacuate 0.5 liters of sweat per day and can go up to several liters! Sweating is a normal and vital phenomenon! It is an essential mechanism, attesting that the body is functioning properly. To correct the smell that emanates or even limit the amount of sweat produced, we got used to applying deodorant, without really understanding this phenomenon.


Origin and benefits of perspiration

There are several reasons explaining this physiological phenomenon.

First of all, sweating can be due to a rise in body temperature following a high surrounding temperature or a physical effort. In this case, sweat plays its role as a regulator of the body temperature, as the body makes every effort to restore its average temperature to 37°C. This is what we call thermoregulation.

Sweating can also be due to a reaction to emotional stress. For instance, it can be the result of a stressful situation. The hormones produced by this stress will then induce the production of sweat.

But that's not all, sweat helps detoxify the body by eliminating certain toxins and also contributes to the formation of a specific biotope, adapted to a characteristic microbiota found in wet areas.

How do we produce sweat?

Sweat is secreted by sweat glands, also known as sudoriferous or sudoriparous glands.There are few millions of them, located under the deep layer of the skin, the dermis. They are distinguished into two types:

Seppic armpits biology

Figure1: Cross-section of the skin with emphasis on the location of the sweat glands 

The eccrine glands are located over almost the entire body with a higher density on the palms of the hands, the soles of the feet and the forehead. They secrete a hypotonic aqueous solution called sweat, and play an important role in thermoregulation, epidermal hydration, cutaneous immunity and epidermal healing. Sweat is composed of 90% water and electrolytes (sodium, potassium, calcium, magnesium, glucose, pyruvate, lactate and antimicrobial peptides).

Following the activation of TRPVs (transient receptor potential vanilloid) in the skin by a thermal stimulus, the central nervous system triggers a parasympathetic response via the hypothalamus which induces sweat production in the eccrine glands. The sweat produced is evacuated by the pores and allows the decrease of the body temperature, the heat attaching itself to the evaporated sweat.

The apocrine glands, on the other hand, are mainly located in the armpits, eyelids, pubis and genitals and breasts. The sweat that they produce is often the result of strong emotions. Its composition is identical to sweat but there are also proteins, lipids and pheromones. 

The apocrine glands are activated by the hormonal system and in particular by androgens, these glands expressing the androgen receptors. As a result, they are only active from puberty and are considered secondary sexual characteristics. The lipids contained in the secretions of these glands are then metabolized by the skin microbiota and are responsible for the development of bad odors.

Why does sweating cause a bad smell?

Contrary to what one might think, sweat is ODORLESS! It is therefore not responsible for the bad smell.

On the surface of the skin in the armpit area, there is a specific microbiota. Some species, composing this microbiota, are responsible for bad odors. Indeed, these bacterial species have enzymes allowing them to metabolize the components of apocrine sweating. This is how they will release malodorous and volatile compounds, such as thio-alcohols at the origin of the characteristic odor of sweat.

Seppic bacteria causing bad odor in sweat

Figure 2: Picture showing how body odour is produced in armpits. - Structural basis of malodour precursor transport in the human axilla - 2018  Credits: University of York and Oxford*

*SOURCE : Structural basis of malodour precursor transport in the human axilla - Gurdeep S Minhas, Daniel Bawdon, Reyme Herman,  Michelle Rudden, Andrew P Stone, A Gordon James, Gavin H Thomas ,  Simon Newstead

Certain bacterial species, which develop preferentially in moist areas such as the armpits, therefore represent the main cause of bad odor, essentially during major episodes of sweating. Depending on lifestyle (diet), body hygiene, menstrual cycle, age, illness... the secretions found in sweat will be different. This is the reason why body odor is not the same.

Whatever its origin, and although sometimes associated with an unpleasant situation, it is important to understand that sweating reflects the proper functioning of the body. Sometimes to better experience this phenomenon, it may be necessary to neutralize the smell of sweat, without blocking sweat production by applying deodorant. While to reduce the production of sweat, a deodorant with antiperspirant properties, will be the best solution. But how to formulate these products and select the right ingredients while taking care of the skin? Here are the next topics to discover now on our blog.

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