Several common substances effectively kill the bacteria responsible for underarm odor, including benzoyl peroxide, rubbing alcohol, aluminum-based antiperspirants, and even baking soda. The odor itself isn’t caused by sweat. It’s produced when bacteria on your skin break down compounds in sweat into smaller, volatile molecules that smell. Killing or reducing those bacteria is the most direct way to control the problem.
Which Bacteria Actually Cause the Smell
Your armpits are home to a dense community of bacteria, dominated by a few key groups: Staphylococcus, Corynebacterium, and Cutibacterium. Of these, Corynebacterium species are most strongly linked to the characteristic smell of body odor. People with higher levels of Corynebacterium on their skin tend to have stronger underarm odor. Staphylococcus species also contribute, though they produce a different, less pungent scent profile. Understanding which bacteria you’re targeting helps explain why some products work better than others.
Benzoyl Peroxide
Benzoyl peroxide is one of the most effective over-the-counter options for killing underarm bacteria. Unlike antibiotics that target specific bacterial structures, benzoyl peroxide is directly toxic to bacteria on contact. It works by releasing oxygen into the skin, which destroys bacterial cells that thrive in low-oxygen environments.
A 10% benzoyl peroxide wash used twice daily reduced skin bacteria by 93.5% within five days and 97.5% by day 15 in one study. A 5% wash produced a more modest 46% reduction over two weeks. For underarm use, most people apply a thin layer of a benzoyl peroxide wash (typically 5% or 10%), let it sit for 30 to 60 seconds, and rinse it off in the shower. Be aware that it can bleach fabrics, so white towels are your friend here.
Rubbing Alcohol
Alcohol is a fast-acting disinfectant. According to CDC data, ethyl alcohol at concentrations between 60% and 95% kills gram-positive bacteria like Staphylococcus aureus within 10 seconds of contact. Standard rubbing alcohol (isopropyl alcohol) works through a similar mechanism, dissolving bacterial cell membranes on contact. Solutions below 50% concentration lose their effectiveness sharply.
The downside is that alcohol evaporates quickly and offers no lasting protection. It kills what’s on the surface at the moment of application, but bacteria repopulate within hours. Some people swipe their underarms with a 70% isopropyl alcohol pad before applying deodorant as a way to start with a cleaner slate. Frequent use can dry out or irritate the skin, especially after shaving.
Aluminum-Based Antiperspirants
Antiperspirants do double duty. They’re best known for plugging sweat glands to reduce moisture, but the aluminum salts they contain are also directly bactericidal. Lab testing has shown that aluminum chloride hexahydrate is highly effective at killing the resident bacteria on underarm skin, including the Staphylococcus and Corynebacterium species responsible for odor. It also persists on the skin, providing ongoing bacteriostatic effects (meaning it keeps inhibiting bacterial growth between applications).
This combination of drying the environment and actively suppressing bacteria makes antiperspirants more effective at odor control than simple deodorants, which typically just mask smell with fragrance or use mild antimicrobials.
Baking Soda
Sodium bicarbonate (baking soda) inhibits bacterial growth by raising the pH of the environment. When bicarbonate enters bacterial cells, it disrupts their internal pH balance. The bacteria then burn through energy trying to restore equilibrium, which slows their growth rate and can reduce their viability. This isn’t the same as the rapid kill you get from alcohol or benzoyl peroxide. It’s more of a suppressive effect that keeps bacterial populations lower over time.
Many natural deodorants use baking soda as their primary active ingredient for this reason. Some people find it irritating, particularly if their skin is sensitive or freshly shaved, because the alkaline pH can disrupt the skin’s own acid mantle.
Prescription Options for Persistent Odor
When over-the-counter approaches aren’t enough, prescription topical antibiotics like clindamycin or erythromycin can be applied directly to the underarms. These are typically recommended for bromhidrosis, the clinical term for chronically excessive body odor. A doctor may suggest a few days of washing with an antiseptic soap combined with one of these antibiotic creams to knock bacterial populations down to a manageable level.
How Killing Bacteria Reshapes Your Microbiome
What happens under your arms over weeks and months of product use is more complex than a simple “kill bacteria, reduce odor” equation. Research from a study tracking armpit microbiomes found that long-term antiperspirant users actually developed more diverse bacterial communities than people who used no products at all. Antiperspirant users averaged about 31 different bacterial types in their armpits, compared to roughly 21 for people who used nothing and only 11 for deodorant-only users.
The shift in species composition is especially interesting. People who used no underarm products had communities dominated by Corynebacterium, the primary odor-causing group. Antiperspirant and deodorant users, by contrast, had communities dominated by Staphylococcus, with over 180% more Staphylococcus than non-users. They also had dramatically less Corynebacterium: non-users had over 335% more Corynebacterium than antiperspirant users. Since Corynebacterium drives the strongest body odor, this shift partly explains why these products work.
When people in the study stopped using their products, bacterial density quickly climbed back toward the levels seen in non-users. The bacterial landscape didn’t snap back to its original composition right away, though. Former antiperspirant users still had Staphylococcus-dominated communities days after stopping. This means there can be an adjustment period if you switch products or stop using them altogether, during which your odor profile may change unpredictably as your microbiome rebalances.
Because antiperspirants have only been widely used for about a century, the bacterial species they favor aren’t the ones that historically dominated human armpits. Whether this altered microbiome has any health implications beyond odor isn’t yet clear, but it’s worth understanding that these products don’t just temporarily suppress bacteria. They fundamentally change which species live on your skin.