It feels like a laundry problem, so that's where everyone fights it: stronger detergent, vinegar soaks, extra rinses, the "sour towel" hacks online. It half-works for a day, then the musty note creeps back into the same favourite shirt — and you quietly move it to the back of the wardrobe.
Here's the part no one explains. After 40, changing skin oils produce nonenal — an odour compound that isn't water-soluble. It sits on your skin, and every time you wear something, it transfers into the fibres. Detergent is built to lift dirt and sweat, not nonenal, so the source survives the wash and re-loads the fabric the moment it touches your skin again. You're not failing at laundry. You're treating the wrong end of the problem.