What is the ruling on a man wearing women's underwear (panties) if they resemble men's underwear in shape, and the purpose of wearing them is to avoid sweat and allergies, not to imitate women?

It is not permissible for a man to wear women's clothing, nor for a woman to wear men's clothing, whether with the intention of imitation or not, as long as the clothing of each gender can be distinguished. It is advised to look for another type of men's clothing.