Is it normal to wear underwear under a swimsuit?
Depends.It depends
Yes, some people wear underwear under a swimsuit, but most swimsuits are designed to be worn on their own. It’s mostly a comfort or modesty preference, though underwear can get soggy and show through.
It’s not unusual, especially if you want extra coverage or support. But swimsuits usually have a lining and are made to be worn without underwear, so you don’t need an extra layer for the sake of hygiene.