Sweat, as it comes from the pores and hair follicles, initially has not an unpleasant odor. Subsequently, when it comes into contact with enzymes (esterases) and bacterial agents, it undergoes a marked degradation and a rapid alteration with the consequent development of volatile substances with unpleasant odor.
The extent of sweating secretion varies from one person to another, while the odor developed is different depending on the body areas. The transpiration of recently washed skin normally has a sweet smell, definitely not unpleasant. As the day goes on, the smell is altered and worsened because of the activity of bacteria and enzymes that cause the formation of substances of decomposition and fermentation.
The products of decomposition caused by bacteria and enzymes are volatile, caustic and irritating; therefore they bring a double damage to our body:
- the volatile fraction gives the bad odor,
- the alkalinized caustic fraction reddens and scales the skin.
The altered sweat gets a pH greater than 7, thus losing its skin-defensive and protective properties.
To prevent and reduce the formation of bad odors, first you have to resort to cleaning. Washing with suitable cleansers is the basic prophylactic means.
However, many people, though washing often and thoroughly, because of heavy sweating or of excessive secretion of sebum, are subject to a high degradation of the sweat with the consequent development of those volatile substances with unpleasant odor described above.
For these subjects, and generally for all those who love hygiene, modern cosmetic science can now offer the second generation of deodorants, able to develop harmoniously four actions:
- antimicrobial (deodorizing),
- (lightly) astringent,
- moisturizing (better, preventing dehydration),
Sweating is an active process that plays a key role in the maintenance of the body heat balance. Through sweating, moreover, toxic substances are carried out of the body. Sweat has also an important emollient function, thus contributing to the formation of surface hydro-acid-lipid mantle and keeping the skin soft and moist. Sweat is secreted by sweat glands, which are divided into Eccrine and Apocrine.
Eccrine glands are spread virtually all over the body surface area (their density per sq cm is particularly high in the soles of the feet, palms of hands and forehead). The function of eccrine glands is to regulate body temperature (thermoregulation), and becomes especially important when the outdoor temperature exceeds that of the body (37 ° C); as a matter of fact, when the external temperature exceeds 37 ° C, the body heat can no longer be dissipated by physical means (convection, conduction, radiation), but only by the evaporation of water by sweating or lung. Moreover, the eccrine secretion also functions as an emunctory detoxifier. Eccrine sweat is odorless and, therefore, does not affect the body odor. It contains 99% of water. It consists of all the plasma components such as urea, ammonia, lactic acid, pyruvic acid and a few amino acids. This eccrine sweat (perspiratio insensibilis) is continuously formed as a function of temperature (amount greater than 500 ml/24 hours) and, together with the sebum, it forms the hydro-acid-lipid film on the skin surface, that gives the skin the typical oiliness and softness.
Apocrine glands are located in the axillary, perimammary, perianal, genital areas, in the abdomen midline, and in the nasal vestibule. Their development is influenced by circulating sex hormones and by age with a tendency to atrophy after the menopause, especially in women. The outlet spot is located in the hair follicle close to that of a sebaceous gland.
The formation of apocrine sweat occurs cyclically (intermittently) and the secretion looks like a viscous, milky liquid, with an acrid odor, rich in organic material of cellular origin, in proteins, glycogen and higher fatty acids. Its reaction is alkaline owing to the presence of ammonia. At the time of secretion, it looks like a sterile, virtually odorless liquid.
It is less than eccrine sweat (about 430 ml/24 hours), but more easily attacked by bacteria, and, therefore, it has the greater responsibility for the production of different body odors.
Sebum and products resulting from the skin micro-desquamation also contribute to the formation of odor.
The odor intensity is also influenced by gender, race, age and the quality and quantity of microorganisms on the skin of healthy people. The odor generally develops quickly around the armpits, as the constantly warm moisture of this area constitutes a field for the growth and development of skin resident bacteria (especially the Gram-positive bacteria: Staphylococci and diphtheroids). The odor, therefore, is simply the result of the combination of substances such as aldehydes, ketones, lactones and fatty acids (caproate, caprylic and propionic acid) degraded and metabolized by the bacteria.
The fight against unpleasant odor can be carried out in various ways: generally, cleansing with soap and water is not sufficient to completely remove from the skin the bacteria responsible for enzymatic degradation of sweat. Likewise, the use of absorbents or perfumes does not solve the problem completely. Moreover, the use of antiperspirant substances bears various tolerance and safety problems. Therefore, most deodorants currently on the market are based on the presence of particular antibacterials capable of reducing the local microbial load. A second valid way to achieve the deodorizing effect is to use substances with anti-enzymatic activity, that can block the chain of reactions that lead to the formation of the odor.