Should I Wear Underwear Under Swim Trunks?

When It Makes Sense

• Good fit: You have a pair of quick‑dry, moisture‑wicking briefs and your swim trunks are loose or made of thin fabric, so extra coverage prevents accidental exposure and adds personal comfort.
• Good fit: You are swimming in a mixed‑gender environment and prefer additional modesty because the trunks are particularly short or see‑through.

When You Should Avoid It

• Warning sign: Your trunks already include a built‑in mesh liner; adding underwear can increase friction, trap water, and lead to chafing.
• Warning sign: You have a skin condition, rash, or are prone to irritation; an extra layer may exacerbate the problem, so minimal contact is safer.

Pros and Cons

Pros

• Provides extra modesty and peace of mind if the trunks shift during activity.
• Can offer additional support for those who find standard swim trunks too loose or unaffordable.

Cons

• Increases the risk of chafing, bulk, and water retention, potentially making swimming feel heavier.
• May be prohibited in competitive settings where only swim‑specific garments are allowed.

Decision Checklist

• Does the swim trunk have an internal mesh liner that already provides coverage?
• Do you have underwear specifically designed for water activities (quick‑dry, low‑friction)?
• Will adding underwear affect your comfort, cause skin irritation, or impact performance?

Alternatives to Consider

Instead of layering underwear, you can choose swim briefs or board shorts with built‑in liners, select tighter‑fit trunks that stay in place, or wear swim‑specific compression shorts that are designed to minimize drag and chafing.

Final Recommendation

If you prioritize modesty, have quick‑dry underwear, and your trunks lack a liner, wearing underwear can be reasonable. For most swimmers, the built‑in liner is sufficient and reduces risk of irritation. Check competition rules if you plan to race, and consult a medical professional for persistent skin concerns.