Deodorants and antiperspirants have been used for a long time. The first products used in the ancient ages were based primarily on fragrances that simply masked body odor. These products gradually evolved into complex chemical compounds containing aluminum and zirconium salts, which are capable of reducing the amount of sweat produced.

As body odor, especially underarm odor, and excessive sweating are perceived unpleasant by most cultures worldwide, underarm care has become more important over the past decades. 

Today, most consumers consider deodorants and antiperspirants to be basic grooming products. Therefore, today these products make up a significant segment of personal care products.

Anatomy and Physiology of Human Sweat Glands
Sweating has a significant biological role for humans. It is regulated by the sympathetic nervous system and is an important body temperature regulator, especially in warm and humid weather climates, stressful situations, or during heavy exercise. 

It also functions to remove waste and toxic by-products from the body. Sweat glands are widely distributed in the skin and according to Gray's Anatomy, most people have several million sweat glands distributed over their bodies providing plenty of opportunity for underarm odors to develop. Sweat glands found in human skin are classified into two different types: eccrine glands and apocrine glands.

1. Eccrine Glands are simple, spoiled tubular glands. Their secretory portion is found deep in the dermis, from which a duct leads directly onto the skin surface. These glands function continuously and are known as the "true" sweat glands since their main function is to control body temperature and electrolyte balance through the evaporation of water from sweat n the body's surface.

Eccrine glands exist and start functioning from birth. These glands are found all over the body, especially on the palms, soles, axillae (underarms), and forehead. They are under psychological and thermal control. Their secretion consists mainly of water with various salts, primarily sodium chloride and potassium chloride; amino acids, peptides, and proteins; and various electrolytic components, such as ammonia, calcium, uric acid, urea, copper, lactic acid, potassium, and phosphorous. 

A warm and humid environment allows for rapid decomposition of the organic materials, which are made of primarily low-molecular-weight, volatile fatty acids and various steroids. These compounds produce recognizable body odors.

2. Apocrine Glands are primarily limited to certain body parts, such as the axilla, anus, and breast. Within the axilla, apocrine glands outnumber eccrine glands by 10 to 1. These are also found in the dermis; however, these are larger than eccrine glands and their ducts open into the hair follicle duct. Apocrine glands also exist at birth; however, they become functional at puberty when the sex hormones are produced. They are usually triggered by emotions, such as excitement, anger, and fear. Apocrine glands produce an odorless viscous secretion, which acquires a distinctly unpleasant odor after bacterial decomposition. This secretion primarily consists of lipids, cholesterol, proteins, sulfur-containing acids, volatile short-chain fatty acids, and various steroids.

As discussed earlier, sweat by itself is odorless. A characteristic odor develops by the activity of bacterial flora on the skin surface. Bacteria break down various chemicals in sweat, resulting in volatile by-products, which have an unpleasant odor. 

The microorganisms present in the underarm area include bacteria, such as Corynebacterium, Streptococcus, propionibacterium, spp, and Micrococcus, as well as yeast, Malassezia. The microorganisms primarily responsible for the production of body odor include Corynebacterium, Streptococcus, and Propionibacteria. 

The human scent is genetically controlled and systematically influenced by dietary and medicinal intake, as well as by the application of fragrance products. Sweat collected from the skin surface contains a diverse range of metabolites, depending on the physiological status of the donor as well as the functional and developmental states of the sweat glands.

Interesting Facts
The loss of excessive amounts of salt and water from the body can quickly dehydrate a person and can lead to circulatory problems, kidney failure, and heart stroke. Therefore, sweating has a cooling effect and is important to maintain the body temperature; however it is also important that people drink fluids when exercising or when outside in high temperatures to make up for the missing water and electrolytes.

Odorless Sweat (Apocrine + Eccrine Glands) --> Decomposition by bacteria on the skin --> Body Odor