How to Get Sweat Smell Out of a Heavy Hoodie

Late August is when it shows up. The hoodie has been fine all summer, then one humid evening it goes on over a damp t-shirt and there it is, a stale note under the arms that a wash cycle didn't touch. The fabric looks clean. It still smells.

Why it survives a normal wash

Fresh sweat has almost no smell. In a 2020 review in Philosophical Transactions of the Royal Society B, Andreas Natsch and Roger Emter describe underarm odour as a two-step job. The apocrine glands in the armpit release odourless precursor molecules, then enzymes from skin bacteria, mainly Corynebacteria and Staphylococci, split those precursors into the volatile compounds you actually smell. The smell is made on the skin, and on whatever is pressed against it.

Those compounds don't all behave the same in the wash. A University of Alberta team, writing in Textile Research Journal in 2020, soiled cotton and polyester knits with three odorants and washed them up to ten times. The polar one, octanoic acid, came out more readily than the two oily, nonpolar ones on both fabrics. Odorants also built up over the first five soil and wash cycles before levelling off. That is the stale note: a residue that one wash reduces but doesn't clear.

The same study has some good news for heavy cotton. Laundering removed odorants from cotton more effectively than from polyester. An earlier Ghent University study in Applied and Environmental Microbiology collected shirts from 26 people after a spinning class, and a trained panel rated the polyester ones as significantly less pleasant and more intense than the cotton ones. Micrococci grew almost only on the synthetics. Cotton is the easier fibre to get clean. It just takes more than a short cold cycle.

Where heavy cotton does make the job harder is bulk. A 400 gsm loopback terry has a dense field of open loops on the inside face, right against the skin, and a lot of cloth for water to work through. Nobody has published a wash test on loopback specifically, so treat this as our reading rather than a finding. It is still why we soak inside out and give it time instead of trusting a quick cycle.

We leave fabric softener out. It works by leaving a coating on the fibres, which is what makes them feel soft. We didn't find settled evidence on whether that coating holds odour on cotton, so we won't claim it does. On the inside of a fleece that is already holding residue, it just isn't doing anything useful.

The soak that actually shifts it

Read the care label first. On the Canadian care symbols set out in the Office of Consumer Affairs guide, the dots in the wash tub give the maximum water temperature, one dot for 30°C and two for 40°C. A triangle with two diagonal lines means non-chlorine bleach only, and a crossed-out triangle means no bleach at all.
Turn the hoodie inside out so the loop face is exposed. This is where the residue sits.
Fill a sink or a tub with warm water, around 30 to 40 degrees, within whatever the label allows. Warmth helps with oily soil. In a 2013 lab study of a detergent lipase, the class of enzyme that breaks down fats, the researchers found higher wash temperatures gave better oil removal from cotton, with the best result at 40°C.
Add a biological detergent, the kind with enzymes listed on the back, at the soak dose printed on the pack. Lipases break oily residue down rather than just pushing it around the cloth.
Push the hoodie under and work the water through the underarms and the neck with your hands. Leave it one to four hours. Longer is fine on cotton.
Wash on a normal 30 degree cycle, inside out, with a second rinse if the machine offers one. No softener.
Air dry it flat or on a rack, out of direct sun.

For lighter colours, oxygen bleach in the soak helps, as long as the label shows a plain triangle or the one with two diagonal lines. Follow the tub for dose and water temperature rather than guessing.

The usual advice for blacks and dark greys is a cup of white vinegar in the rinse. We couldn't find a controlled study showing it removes body odour from cotton, so file it under folklore. It is popular, not proven. If you try it, keep it out of any water that has oxygen bleach in it. We haven't seen that combination tested either, and there is no reason to run an experiment on a hoodie you like.

No chlorine bleach on a dyed hoodie. It strips colour, and if the triangle on the label has lines through it or a cross over it, the maker has already ruled it out.

The yellow crust under the arms

That stiff, slightly yellow patch is antiperspirant residue built up with sweat and body oil. Antiperspirants work with aluminium salts, and University of Georgia extension guidance notes that products containing substances such as aluminium chloride are acidic and can change the colour of some dyes. It is not a stain in the usual sense, and more detergent on its own rarely shifts it.

The UGA guidance starts simple: rub undiluted hand dishwashing liquid into the patch, then launder. Try that first. If it is still there, make a paste of oxygen bleach and a little warm water, work it into the patch with an old toothbrush, leave it thirty minutes, then run the soak above. Two rounds is normal on a patch that has built up over a season. On dark cloth, test on the inside hem first.

The same guidance is blunt on one point. Never iron or apply heat to a deodorant stain. That means no hot dryer until the patch has gone, because heat makes it harder to move.

Keeping it out

Let deodorant dry properly before the hoodie goes on. Wet residue transfers straight into the loops.
Hang it to air after wearing rather than folding it warm into a drawer.
Never leave it balled up damp in a bag overnight. Odour is bacterial work, and it needs time. The Ghent researchers left their worn shirts for 28 hours before testing them. A gym bag does the same thing for free.
Wear a t-shirt under it. It takes most of the sweat and oil, and a t-shirt is far easier to wash than 400 gsm of fleece.
Wash it before it smells, not after. The Alberta study saw odorants accumulate over repeated soil and wash cycles. Once the residue has built up, you are doing the soak.

None of this is aggressive. Warm water, enzymes and time do the work, which is the same principle behind everything in our care notes. If the wash itself is the worry, washing a hoodie without shrinking it covers the temperatures in more detail.

Sources

Natsch, A. and Emter, R. "The specific biochemistry of human axilla odour formation viewed in an evolutionary context." Philosophical Transactions of the Royal Society B: Biological Sciences, 2020. pmc.ncbi.nlm.nih.gov/articles/PMC7209930
Abdul-Bari, M. M., McQueen, R. H., de la Mata, A. P., Batcheller, J. C. and Harynuk, J. J. "Retention and release of odorants in cotton and polyester fabrics following multiple soil/wash procedures." Textile Research Journal 90 (19-20), 2020, pp. 2212 to 2222. University of Alberta repository copy: ualberta.scholaris.ca/handle/123456789/17230
Callewaert, C., De Maeseneire, E., Kerckhof, F.-M., Verliefde, A., Van de Wiele, T. and Boon, N. "Microbial Odor Profile of Polyester and Cotton Clothes after a Fitness Session." Applied and Environmental Microbiology, 2014. pmc.ncbi.nlm.nih.gov/articles/PMC4249026
Chauhan, M., Chauhan, R. S. and Garlapati, V. K. "Evaluation of a New Lipase from Staphylococcus sp. for Detergent Additive Capability." BioMed Research International, 2013. pmc.ncbi.nlm.nih.gov/articles/PMC3782757
Office of Consumer Affairs, Innovation, Science and Economic Development Canada. "Guide to Apparel and Textile Care Symbols." Page modified 2024. ised-isde.canada.ca
University of Georgia College of Family and Consumer Sciences, Extension. "Remove Stains From Antiperspirant, Deodorant." fcs.uga.edu