It is a common misunderstanding that sweat is the source of body odor, but the liquid released by the body is actually odorless. The unpleasant scent develops when microscopic organisms on the skin consume components within the perspiration. Understanding the different mechanisms used by underarm products is the first step in effectively managing personal hygiene. This requires a closer look at the biological process that creates odor and the distinct ways deodorants and antiperspirants address the issue.
Body Odor and Bacterial Activity
The human body has two main types of sweat glands: eccrine and apocrine glands. Eccrine glands are distributed across most of the body and produce a sweat that is primarily water and salt, which helps cool the body through evaporation. Apocrine glands are concentrated in areas like the armpits and groin, and they become active after puberty. Apocrine sweat contains proteins, lipids, and steroids, making it thicker than eccrine sweat.
This nutrient-rich apocrine sweat is naturally odorless when it is first secreted, but it becomes the food source for the native bacteria on the skin surface. As these microorganisms, such as certain species of Corynebacterium, break down the fats and proteins, they produce volatile organic compounds, which are the source of the familiar body odor. The warm, moist environment of the armpit, combined with this specific composition of apocrine sweat, provides an ideal habitat for the bacterial activity that generates the smell.
Deodorant’s Antimicrobial Action
Deodorants kill bacteria, which is their primary mechanism of action. Deodorants are classified as cosmetics and work by inhibiting the growth of or killing the odor-causing bacteria on the skin.
Many deodorants contain antimicrobial agents, such as alcohol or newer compounds like triethyl citrate, which create an environment hostile to bacterial life. Alcohol is a common base because it quickly dries the area and has an immediate antiseptic effect, making the skin surface less hospitable for microbial colonies. Other ingredients, like acidifiers, are included to lower the local pH of the armpit, which inhibits the proliferation of odor-forming bacteria. By reducing the population of these microorganisms, the deodorant prevents the breakdown of sweat components into volatile, odorous molecules.
Antiperspirants and Sweat Gland Blockage
Antiperspirants operate on a fundamentally different principle than deodorants by targeting moisture rather than microbes directly. They are regulated by the U.S. Food and Drug Administration (FDA) as over-the-counter drugs because they affect a bodily function—sweating. The active ingredients are aluminum-based salts, such as aluminum chlorohydrate or aluminum zirconium complexes.
When applied, these aluminum salts dissolve in the sweat and form a temporary, gelatinous plug near the top of the sweat duct. This physical obstruction prevents or significantly reduces the amount of sweat that reaches the skin’s surface. By blocking the flow of perspiration, the antiperspirant effectively starves the odor-causing bacteria of their necessary food and moisture source. This reduction in wetness is the main action, though some antiperspirant formulations may also possess mild antimicrobial properties.
Selecting the Appropriate Product
The choice between products depends on the user’s main concern: odor or wetness. If the primary goal is odor control, a deodorant is the appropriate selection, as it uses antimicrobial agents to eliminate scent-producing bacteria. Deodorants allow natural perspiration to occur, which is a normal function of body temperature regulation.
If controlling underarm wetness is the main priority, an antiperspirant is necessary because only the aluminum-based salts can temporarily block the sweat glands. Many products combine both functions and are labeled as deodorant/antiperspirant hybrids, offering sweat blockage, antimicrobial action, and fragrance. Individuals with sensitive skin may opt for aluminum-free deodorants that use natural ingredients like baking soda or essential oils to manage bacterial growth and absorb moisture.