No Stupid Questions

A couple of other people have commented on this, but no one's fully explained the mechanism, so:

Fabric that's petroleum-derived like polyester and most other synthetics traps odors and resists washing in ways that natural fibers don't. Some people think this is because synthetics are less breathable than natural fibers, and while this is often the case, that's not actually the main cause. Rather, this is because being oil-derived makes the fibers water-resistant, which keeps them from being thoroughly cleaned, and also traps body oils, resulting in food for odor-causing bacteria.

Here's a good video explaining this in more detail, for the curious: https://www.youtube.com/watch?v=zJVYTnFjiFg

Honestly, I don't think there's much to do about that one beyond making sure to get 100% natural fiber clothes. As a bonus, it's often less irritating to the skin and helps reduce a major source of micro plastics.

Some antiperspirants are further much tougher to wash off and will tend to resist washing, but I don't know the mechanism behind this one, so I can't really advise on it, apart from saying that I've not encountered the issue with natural deodorants.

I work out in sleeveless tops.

Had a friend who swore by ammonia for armpit stains on shirts, maybe try that?

You may need a different detergent or a detergent booster that works harder on stains. Usually they're peroxide based, but contain other agents as well. Some come in powder form and others in sprays.

One powder I grabbed does brighten better than detergent alone and makes things smell like an honest-to-goodness laundry. (Which I'm not going to name because this already sounds like a sales pitch. It isn't. It's just something that was on special offer on my supermarket's website and I added it to my virtual basket because I have a few blood-spotted items of clothing that regular washing wasn't getting out.)

It worked wonders on some very greyed white t-shirts, but not so great on the blood spots on coloured clothing. I may need to soak them for longer or use more additive, risking the colour, which I may have been too cautious about up to the present.

Looked into this recently bc I felt like I couldn't get my ex's odor off my clothes. Based on my fav laundry guy (jeeves_ny) on IG, I found Persil and Ariel to be the answer. Feel like I smell like myself again after years.

After the clothes are clean but still wet, add some distilled white vinegar and run the rinse cycle again, or catch the washer before the rinse cycle and add before the rinse starts.

When I have issues with the underarms of my workout shirts coming out still discolored from sweat+deodorant, I like to take a small amount of laundry detergent = just enough to dampen the areas needing extra help. Then I put it in the washer, add my detergent for the load, with a presoak setting so the clothes all soak in the water and detergent for 15 minutes before the wash cycle actually starting.

Use spray on or gel deodorant. It helps a lot.

Wash stinky, sweaty, greasy clothes in hot, it helps dissolve those things. Add at least 1/2 cup baking soda to the drum (front or top loading), this cuts grease and smells. It also helps boost the detergent and does not ruin clothes. Wash super dirty clothes on a heavy cycle. If they still stink after that, you need to replace those clothes. Plastic clothes will eventually get nasty.

Why not exercise in a vest/tank top and let your armpits breath?

Ive bought for my wife a potassium aluminium rod from a pharmacy to use on the armpits. No white marks after using. Also it does not have any scent and does not irritate the skin. No sweat scent either. You could try that for new shirts. If there won't be any information on the packaging. Rinse the rod whit water, applay on skin and leave the rod to try completely.

This happens when you pack HE washers too much. For your stinky clothes you need to do smaller loads, and possibly add in some kind of oxygen bleach booster.

I used to have this on my undershirts. It's 100% anti-perspirant.

If you don't mind sweating, switch to just deodorant. There's a difference. Anti-perspirant cakes and stains to keep your sweat from becoming liquid. Deodorant just stops smell, and the sticks usually aren't pure white.

I use a salt stick deodorant and it's great IMO. That's the same thing as the "potassium aluminum rod" sometime else mentioned. Easy to find, never even know it's there.

Wash your whites in hot water and white vinegar, then usual wash with oxyclean, to get rid of the stains in what you have.

A human buying antiperspirant is like Superman buying kryptonite. Sweating is one of our biggest super powers. Learn to love it. Shower before you work out, and you won't stink.

Sorry, this is more about some of the comments than OP, who never mentioned stinking.

Vinegar and sodium bicarbonate, scrub a little and throw it in the washing machine. Let it rest for about 15 minutes before start washing.

Some of the other tips are covered (aluminum in deodorant is a big cause of stains) so I'd recommend clothing made of natural fibres like cotton, bamboo and wool. They have natural antibacterial properties and are easier to strip stains out of with basic detergents and vinegar.

Quit all that working out nonsense