Why Does Underarm Odor Occur?

Freshly released sweat from your armpits is generally odorless. The long-chain fatty acids produced there are too large to become airborne. If you were to smell a gallon of sweat directly from your underarms, it might not even register as an unpleasant scent. Odor arises when sweat interacts with the skin's microbiome, where bacteria and hormones break down these fatty acids into smaller, volatile, and odorous molecules. The primary microorganisms responsible for underarm odor include:

1. Corynebacterium: These bacteria are prevalent on the skin but are not typically found on clothing, which suggests they’re not the culprits behind the odor in fabrics.
2. Staphylococcus: Present in similar amounts on both skin and clothing, they do contribute to body odor, but they are less significant when it comes to clothing smells.
3. Micrococci: Found on the skin and particularly thrive on synthetic fabrics like polyester and nylon, these bacteria are mainly responsible for the unpleasant odors in your favorite shirts.

The Science Behind Polyester Odor

Research conducted by Callewaert and his team in 2014 tested microbial growth on freshly washed shirts after intense exercise. They discovered that micrococci flourished in nearly all synthetic shirts but were absent in cotton items. “Micrococci thrive better on polyester,” Callewaert explained upon releasing his findings.

Furthermore, polyester and its blends produced a far stronger odor according to a trained odor panel's assessments. The synthetic materials emitted scents described as musty, ammonia-like, and sour, contrasting sharply with the fresher odors of cotton.

A 2020 study by Mukhtar Abdul-Bari at the University of Alberta corroborated these findings, revealing that polyester retains odors more stubbornly than cotton. “Polyester doesn’t easily release those sweat-related compounds, and repeated wear intensifies the accumulation of odor,” he noted. Being a non-polar fiber, polyester repels water, allowing it to dry quickly but also attracting skin oils that contribute to body odor.

Synthetic materials like polyester create a warm, moist environment that fosters bacterial growth, while cotton quickly absorbs moisture, reducing the opportunity for odor to develop.

Effective Strategies to Combat Odor

Although you may not always smell fresh after a workout, certain strategies can help mitigate unpleasant scents:

1. Air Dry Clothes Immediately: Avoid leaving sweaty garments piled up where air can't circulate, as heat can amplify odors. Turning clothes inside out can also help release trapped smells.
2. Pre-Treat with Vinegar: Soaking workout clothes in a vinegar-water solution (1 part vinegar to 5 parts water) for 30 minutes can help before washing. Always wash using the warmest temperature suitable for the fabric.
3. Avoid Liquid Fabric Softener: While useful for cotton, fabric softeners can trap odors in synthetic fabrics and compromise their elasticity.
4. Incorporate Laundry Sanitizers: Using a laundry sanitizer weekly can help prevent the buildup of odor-causing bacteria, with phenolic disinfectants being gentler on fabrics than chlorine bleach.
5. Skip the Dryer: Air-drying your activewear after washing is ideal for prolonging the life of the clothes and keeping odors at bay, as machine drying can set unpleasant smells.

Looking Ahead: Microbiome Innovations

Callewaert is optimistic about future solutions to body odor, including microbiome transplants. He successfully transferred the microbiome of a non-smelly identical twin to his brother, resulting in a significant reduction in odor within weeks. He is now exploring microbiome transfers among unrelated individuals.

Instead of wishing for the absence of the ABCC11 gene, which is present in most East Asians and 2% of those of European descent, you can take simple steps to keep your clothes smelling fresh. Interestingly, those without this gene may have dry ear wax, which is less effective and more prone to clogging than the wet variety that most of us produce.

In this informative video, "The Reason Polyester Clothes Get So Stinky," we delve into the science behind why polyester can cause unpleasant odors and what you can do about it.

Discover practical solutions in "7 Ways to Get RID of STINKY Odors in Clothes!" This video provides tips to help you keep your clothing fresh and odor-free.