Why Does My Polyester Workout Shirt Still Smell After Washing?

The shirt has been through the wash. Once it dries, the underarms still smell. Before changing your deodorant again, check the fiber label and the washing instructions: the garment itself can retain material that contributes to odor.¹²

What polyester holds onto

In a 2021 laboratory study, researchers compared cotton and polyester using a controlled mixture of sweat, sebum and skin bacteria. Sebum is the oily material produced by your skin. Polyester absorbed more sebum than cotton, and bacteria were more active in the polyester.¹

Under the microscope, the oil spread along polyester fibers. In cotton, it collected in droplets. The researchers proposed that polyester’s oil distribution made nutrients more accessible to bacteria.¹

Drying did not make either textile bacteria-free. Bacteria became strongly attached to both fabrics as they dried. Cotton therefore isn’t a guarantee against retained bacteria or odor.¹

These were laboratory fabric samples, not a trial of women washing their own gym shirts. The findings help explain the mechanism. They do not tell you which detergent will rescue a particular top.¹

What a wash removed in one study

A separate 2016 study measured six odor-related volatile compounds in used socks and T-shirts before and after washing at 20°C with unperfumed washing powder. Reductions after washing, while the items were damp, ranged from 16% to 100%, depending on the compound and sample. For T-shirts assessed after drying, reductions from the original prewash measurements ranged from 25% to 98%.³

Those numbers describe chemical concentrations, not a percentage improvement in how pleasant a shirt smelled. They also do not establish that every cold wash fails, or that a hotter wash will fix your shirt. The finding is narrower: under those conditions, laundering removed some compounds more completely than others.³

Check the load before buying another product

Whirlpool’s² care guidance lists several possible contributors to lingering workout-clothing odor: insufficient detergent, an overloaded washer, incomplete drying, and a washer that needs cleaning. Its recommendations include checking the garment label and turning workout clothes inside out before washing.²

Start with the instructions you can compare against what you actually did:

• The shirt’s care tag: check the permitted washing and drying conditions before changing the temperature.
• The detergent directions: check the dose you used for that load.
• The washer instructions: check loading and cleaning guidance, especially if several items come out smelling.
• The dry shirt: check whether the odor persists after drying is complete.²

This is appliance-care guidance from a manufacturer that sells washers. It is useful for checking a washing routine, but it is not a comparative detergent trial.²

The play

Try this: record the shirt as well as the sweat

For your next few wears, note which shirt you wore, its fiber composition, whether it smelled before wear, and what happened after washing. Keep your deodorant the same while you compare shirts, so you have fewer changes to untangle.

If you’re considering an odor-resistant replacement, our guide to antimicrobial clothing labels explains what those claims cover.

Arms Up discusses fabric choices and includes a Fresh Log for tracking the zone, pattern and changes you try. Use it to record whether the smell follows one top or several. See the book.