You can't. Cotton trousers can't be worn as underwear. Underwear and cotton trousers have different constellations. Cotton trousers are trousers made of chemical fiber, pure cotton and other materials. When the temperature is cold, they are worn under the outer trousers to keep warm. In the north of Huaihe River, they are collectively called "autumn trousers". Bloomers generally refer to underwear, which is divided into men's wear and women's wear. And there are more and more styles according to gender. Wearing underwear appears in different countries at different times.