How Does Aluminum-Free Deodorant Work?

Short Answer: Aluminum-free deodorant controls odor without reducing sweat, using ingredients that target odor formation, odor release, and freshness.

Aluminum-free deodorant is designed to fight body odor without using aluminum-based active ingredients used in antiperspirants. Unlike antiperspirants, which use aluminum salts to temporarily reduce the amount of sweat reaching the skin’s surface, aluminum-free deodorants focus on the biological and chemical processes that cause odor.

At Old Spice, our aluminum-free deodorants are designed around a fundamental scientific fact: fresh sweat is largely odorless. Underarm odor develops when naturally occurring skin bacteria transform components of sweat into volatile, odorous molecules.^1-4

Old Spice aluminum-free deodorants use complementary odor-control mechanisms that may include:

• Fighting odor-causing bacteria by preventing the growth of S. epidermidis, S. hominis, and C. tuberculostearicum
• Devolatilizing acidic odor molecules so they don’t evaporate
• Providing fragrance that supports the perception of freshness
• Pairing primary and secondary fragrances for 24/7 freshness

Together, these approaches effectively manage odor to keep you fresh 24/7.

Why Does Underarm Odor Happen?

Short Answer: Fresh sweat is largely odorless; underarm odor develops when skin bacteria convert sweat components into volatile odor molecules.

Sweating is part of the body’s natural process for regulating temperature. Although sweat contains water, salts, lipids, amino acids, and other components, freshly produced sweat is largely odorless.^1,3,4

Odor develops when bacteria living on the skin metabolize components of underarm sweat. Through this process, bacteria generate volatile molecules that can leave the skin, evaporate into the air, and reach odor receptors in the nose.^1–4

Several compounds have been identified as most frequently associated with underarm odor, including:^1–4,8

• Sulfur-containing compounds such as 3-methyl-3-sulfanylhexan-1-ol, or 3M3SH
• Branched-chain fatty acids
• 3-methyl-2-hexenoic acid, or 3M2H
• 3-hydroxy-3-methylhexanoic acid, or HMHA
• Isovaleric acid, or IVA^{2, 8}

The amount and type of bacteria present in the underarm, part of your body’s unique microbiome, can influence the dynamic mix of odor-causing byproducts released. Certain bacterial populations, including specific commensal Staphylococcus species, like S. hominis, have been associated with differences in body odor.⁴

However, the underarm microbiome is a complex ecosystem, and not every bacterial species contributes to odor production to the same extent. This is why the ultimate goal is not necessarily to eliminate all bacteria. The goal is to help reduce the bacterial activity and chemical processes that generate noticeable odor.^3,4

How Glycols Help Control Odor

Short Answer: Glycols are versatile, electrically neutral ingredients whose water- and oil-compatible properties support deodorant structure, feel, and performance.

Glycols are organic molecules containing two hydroxyl (-OH) groups attached to a hydrocarbon backbone. Variations in the length and structure of this backbone influence the physical and chemical properties of individual glycols. Importantly, the hydroxyl groups present in glycols are chemically distinct from free hydroxide ions (OH⁻), which contribute to alkaline (basic) pH. Consequently, glycols are typically electrically neutral molecules that do not substantially raise pH on their own.

Propylene glycol and dipropylene glycol, for example, are commonly observed in antiperspirant & deodorant categories and are known for their ability to create topical products with desirable skin-feel, product structure, and shelf life.

The glycols commonly used in personal care products are generally small, electrically neutral molecules. Their hydroxyl groups readily form hydrogen bonds with water, while their hydrocarbon portions are more compatible with less polar materials and other hydrophobic ingredients. This balance of polar and nonpolar character contributes to their versatility within deodorant formulations.

This combination gives certain glycols an amphiphilic character, meaning that the molecule has both water-loving and lipid-loving properties. Different glycols can be used in combination with water and other carrier fluids to tune the properties of the deodorant.

• The polar hydroxyl groups support interaction with water and other polar materials.
• The nonpolar hydrocarbon portion can be tuned to dissolve ingredients like fragrance while maintaining desirable structure and aesthetics.
• The relatively small molecular size makes them semi-volatile, so they don’t leave your skin’s surface feeling wet at application.

These properties of glycols also make them useful in managing the activity of odor causing bacteria.

How Glycols Affect Bacterial Membranes

Short Answer: Certain glycols can interact with bacterial membranes, disrupting normal membrane function and reducing odor-producing bacterial activity.

Underarm bacteria are single-celled microorganisms, meaning each bacterium consists of just one independently functioning cell. Although microscopic, these cells contain all the components necessary for survival, including their own genetic material and enzymes.

A critical structure of these bacterial cells is the lipid membrane, which surrounds the cell and acts as a selectively permeable barrier. This means that the lipid membrane allows certain components to penetrate its exterior ‘wall’. The membrane is primarily composed of phospholipids, amphiphilic molecules that contain a water-attracting (polar) head, and a water-repelling (nonpolar) tail. This arrangement forms a flexible bilayer that protects the cell while controlling what enters and exits. The membrane helps bacteria maintain hydration, transport nutrients, remove waste, generate energy through electrochemical gradients, and preserve the internal conditions required for life.

Certain glycols can associate with bacterial cell membrane structure and disturb how tightly its components are organized. Reduced bacterial activity can be associated with increased membrane permeability and loss of normal membrane function.⁵ Reviews of glycol’s effectiveness in odor protection show that performance depends on the glycol, concentration, target organism, test system, and formulation conditions.⁶

• The polar hydroxyl groups can interact favorably with the polar headgroups of phospholipids in the bacterial membrane.^5,6
• The nonpolar hydrocarbon portion supports interaction with the lipid interior of the bacterial membrane.^5,6
• The relatively small molecular size may allow the molecule to more easily make the journey from product to the surface of bacteria, by having useful mass transport properties such as high diffusion coefficient.
• Glycols with longer hydrocarbon portions may interact more strongly with lipid membranes, although activity depends on concentration, formula environment, and the specific organism being tested.^5,6

When bacterial membrane integrity is disrupted:

• Essential cellular contents may leak out.^5,6
• External materials may enter the bacterial cell in an uncontrolled way.^5,6
• Nutrient transport can become less efficient.^5-7
• The cell may have difficulty maintaining ion balance.^5-7
• Energy-producing processes may be impaired.^5-7

By reducing bacterial viability or activity, glycols can help decrease the conversion of odorless sweat components into volatile odor molecules.^5,6

Old Spice Aluminum-free deodorants leverage various blends of glycols to effectively manage odor while balancing this against other formulation considerations. Depending on the choice of glycols this will lead to deodorants with varied hardness, glide, skin feel, fragrance expression, and odor-causing bacterial control.

Why pH Matters in Odor Control

Short Answer: A higher-pH environment can interfere with bacterial energy processes and shift acidic odor molecules into less volatile forms.

Bacterial cells must maintain a controlled difference between their internal environment and the environment outside the cell.

One component of this difference is the proton gradient. Protons are positively charged hydrogen ions. A proton gradient is a difference in proton concentration across the cell membrane, resulting in an ability to move compounds across the cell membrane via passive (moving with the concentration gradient) or active transport (moving against the concentration gradient). This is called the proton motive force, or PMF. Bacteria use the proton motive force, or PMF, to support processes such as:

• ATP production
• Nutrient acquisition
• Ion balance
• Motility in certain organisms
• Cellular homeostasis⁷

Many bacteria maintain an internal pH that is higher than the surrounding environment. Raising the pH outside of bacterial cells reduces the proton motive force and may make it more difficult for susceptible bacteria to maintain the gradient needed for normal metabolism.⁷

A useful analogy is a hydroelectric dam. The dam produces energy because water moves across a height difference. If that difference is reduced, the system has less energy available. Similarly, weakening the proton gradient can interfere with the energy bacteria need to grow and metabolize odor precursors.⁷

What Sodium Stearate Contributes

Short Answer: Sodium stearate gives the stick structure and helps maintain an alkaline formula environment that supports odor control.

Sodium stearate is the sodium salt of stearic acid. Generally, salts are compounds constituted upon interaction of positively and negatively charged ions, resulting in formation of three-dimensional crystalline lattice structures. It is commonly used to create the solid gel structure of clear or translucent deodorant sticks, but its chemical properties can also contribute to the formula’s overall odor-control.

Sodium stearate contains:

• A long, nonpolar 18-carbon hydrocarbon tail
• A polar, negatively charged carboxylate head group
• An overall amphiphilic structure (water- & lipid-loving ends).

The long hydrocarbon tail interacts with oils and other nonpolar materials, while the charged head group interacts with water and polar components. This structure allows sodium stearate molecules to organize into networks that help give a deodorant stick its structure and application feel. Most of our ingredients, like glycols and water, are liquids, but the sodium stearate provides the structure that makes our sticks solid.

Because sodium stearate is the salt of a fatty acid, formulas containing it are typically maintained under alkaline conditions to preserve the desired structure and performance.⁷

Within an alkaline formula, sodium stearate supports odor control by:

• Contributing to a higher-pH formula environment: This more alkaline environment can reduce the proton motive force that susceptible bacteria use to support normal metabolism, helping limit the production of odor-causing byproducts.⁷
• Much like glycols, the amphiphilic nature of sodium stearate may help to disrupt the phospholipid membranes of odor causing bacteria, leading to less production of odor.^5,6

What Magnesium Hydroxide Contributes

Short Answer: Magnesium hydroxide gradually raises local pH, helping limit susceptible bacterial processes and reduce the volatility of acidic odorants.

Magnesium hydroxide is an inorganic base composed of positively charged magnesium ions and negatively charged hydroxide ions.

Its relevant chemical characteristics include:

• Alkaline in solution: As magnesium hydroxide releases hydroxide ions, it increases local pH, which can make conditions less favorable for susceptible bacterial processes and convert some neutral, acidic odor molecules into charged forms that are not volatile, keeping them from evaporating into the air where they can be smelled.^7,8
• Low solubility in water: Because only a limited amount dissolves at a given time, undissolved magnesium hydroxide can remain available as a reservoir, supporting gradual alkalinity as moisture is introduced during wear.
• Capacity to release hydroxide ions as material dissolves: These ions combine with available protons, lowering proton concentration and helping sustain the higher-pH environment associated with reduced odor formation and reduced odorant volatility.
• Ability to neutralize acidic compounds: By converting acidic odorants into their corresponding charged salts, magnesium hydroxide can reduce their tendency to enter the air and reach odor receptors in the nosee.