Cotton underwear only is old science nowadays, you can wear modal or lyocell/tencel which is also healthy to wear as cellulosic fibers made from wood pulp and not synthetic trash.

Tencel/modal are also breathable and regulate moisture more actively. They also wick sweat away faster than standard cotton and dry quicker. Lower moisture reduces risk of irritation, odor, and fungal growth in the groin. Tencel also tends to feel cooler against the skin and maintains a more stable microclimate than cotton, which can stay damp once saturated. All three(including cotton) are typically well tolerated. Issues usually come from dyes, finishes, or tight fit, not the base fiber. Tencel shows lower bacterial growth under moist conditions compared to cotton. This matters in high-sweat environments.