Should I Wear Underwear Under Swim Trunks?

When It Makes Sense

• Good fit: When the swim trunks are made of thin, quick‑dry material and you want extra modesty or a hygiene barrier for mixed‑gender environments.
• Good fit: When you have a medical condition such as sensitive skin, recent surgery, or a need for added protection, a thin breathable underwear layer can provide comfort.

When You Should Avoid It

• Warning sign: When the trunks already include a built‑in mesh liner; adding underwear can create friction, leading to chafing or skin irritation.
• Warning sign: When you are engaging in high‑performance swimming or water sports where extra fabric increases drag and slows drying, making a swimsuit less efficient.

Pros and Cons

Pros

• Provides an additional hygiene barrier, reducing direct contact with pool water and potential bacterial exposure.
• Offers modesty for swimmers who prefer more coverage, especially in public or mixed‑gender settings.

Cons

• Extra fabric can bunch, cause chafing, and create drag that hampers swimming efficiency.
• Swimwear dries more slowly with an additional layer, which may be uncomfortable after leaving the water.

Decision Checklist

• Does the swim trunk have a built‑in mesh liner that already provides coverage?
• Will the extra layer affect your performance or comfort during the intended activity?
• Do you have any medical or personal modesty needs that justify wearing underwear?

Alternatives to Consider

Instead of regular underwear, you can choose swim‑specific briefs or a thin, moisture‑wicking liner designed for water use. Some swimmers prefer boardshorts with a sewn‑in liner, while others opt for classic swim briefs that already deliver coverage without extra fabric.

Final Recommendation

For most casual swimmers, relying on the built‑in liner of quality swim trunks is sufficient. Wear underwear only when you need extra modesty or have a medical reason, and select seamless, quick‑dry underwear to minimize discomfort. If performance or comfort is a priority, choose swim‑specific inner liners or trunks with appropriate built‑in coverage.