Middle aged women (a.k.a. Generation X) have stopped wearing panties in large numbers. About 20% no longer wear them even once a week. The numbers aren't quite as great in younger generations, but are much higher than you might naively expect.
Meanwhile Millennial women have in the last few years fairly abruptly decided that they usually won't wear bras in large numbers, a trend that has sent Victoria Secret's holding company's stock into a tailspin. And, it isn't just American women either. Bras are also on the decline in Japan.