Can you swim in period underwear?

Everyday period underwear is not designed for swimming — in water, the absorbent core can't work properly and would just fill with water. For the pool or sea, you need purpose-made period swimwear, or use a tampon or menstrual cup.

A good approach is to wear period swimwear (or a tampon/cup) in the water, then change into regular period underwear before and after your swim for comfort and protection.