Sometimes with certain synthetic fabrics odors seem to chemically bond to the fabric.
I experienced this many years ago at the end of a backpacking vacation. My wife insisted that we stop at a laundromat before our flight home.
We didn't have any unscented detergent with us and we assumed the laundromat would have unscented stuff available in those coin-op machines. They did not. All they had for sale was the extremely putrid perfumed garbage.
So not only did we wash some synthetic base layers in the stuff, we also laundered in machines that reeked of "fresh ocean vomit" or some other stupid, made up name that marketers dream up.
We washed both synthetics and cotton clothes and when we were done, it all reeked to high heaven. After several more washings back home the stench of the perfume in the cotton clothes dissipated but it took literally years before I could no longer smell the synthetics. It got to the point where I would toss those synthetics in a load of laundry even if they hadn't been worn since the last washing and it still took a long time to become "odorless".
I refused to wear those clothes while hunting and in those days, they were the only base layers I owned. So I had to buy new base layers which were dedicated strictly for hunting and nothing else, and they are cared for with kid gloves. Always laundered separately, and always air-dried, never dried in a machine. I believe the heat helps bond odors to synthetic fabrics, plus dryers are hard on clothes. Synthetics air-dry quickly so I see no reason to shorten their life by repeatedly drying in a machine. Hang them on the line in front of a fan and they'll be dry almost as fast as a clothes dryer.
We use zero scented laundry products and I never wash them in a machine that isn't mine.
Once a synthetic has been contaminated, I believe the only remedy is time and sunlight. Hang it outside in the sun, rain and fresh air for a few months. Even wearing it will help if you can stand the perfume odor.
I'm extremely resistant to buy used hunting clothing from classifieds. Thrift stores might be okay because you can sniff before you buy but the classifieds is risky, especially for expensive, high-end clothing.No matter what promises the seller claims, don't believe it until you have it in-hand and then be prepared to relegate perfumed clothes to work wear or some other use like making rags.
Side note:
I've had some substantial inflammation issues for the last 13 months and my wonderful wife has been on a major mission to cure me. She is a researching machine.
She recently read about studies that addressed how some people have severe reactions to strong scents and perfumes which can cause all sorts of autoimmune responses. I know that when I'm in the grocery store and I have to walk down the household product aisle, it's very uncomfortable for me. It seems like my body is trying to reject those odors to the point that I resist walking down those aisles.
My point being...I'm bewildered as to why our society seems to be so enamored with chemically scented products. I have no doubt that, for some people, they are a health issue yet to be discovered or pin-pointed.
Hey, many therapists use specific, controlled aroma therapy to treat certain conditions so it stands to reason that chemical perfumes could have an effect on the health of some people.
STOP USING THE SH!+. Gotta reduce our use of chemicals!