Although it may seem like a simple question, many people wonder if they should wear underwear under their one-piece swimsuit or swim trunks. As a competitive swimmer, swim coach, and avid beachgoer, I can help you figure out if you need underwear when you swim.

So, should you wear underwear underneath swimwear? In general, you should never have to wear any underwear under your swimsuit. If it is a one piece, you don’t need to wear a bra or panties. If it is swim trunks, swim shorts or swim briefs, you usually shouldn’t wear underwear underneath those either.

Many people may want to know why you shouldn’t wear any underwear under swimsuits. Isn’t it too revealing and uncomfortable without additional cover? In reality, you are more covered up than you think you are. Here are more details about how the swimsuits are built to act as both under and outerwear.

Swimsuits vs Underwear: Use in Water and Transparency

Swimsuits are made with certain types of material that are suitable for water use and can also withstand harsh pool chemicals like chlorine. Additionally, they absorb less water and dry out faster.

Most non-pool water appropriate undergarments are made from less durable materials such as cotton, and can be easily ruined by pool water. Regular underwear will also absorb a significant amount of water, which increases drag and makes swimming more difficult. Extra water retention will also increase drying time of the garment. 

Swimsuits are specifically made to eliminate the need for wearing underwear. Women’s swimsuits generally have special lining and additional padding in the bust and crotch areas. Both are added to make the swimsuit more comfortable and to prevent visibility of one’s private areas.

Here is how to check for lining: take your swimsuit and turn it inside out. Look for a second layer of material under the main layer (it is usually white, but can be any color). Try separating the second layer of the material with your fingers – the lining should easily separate.

Along with lining, recreational swimwear tops can have an underwire for additional support in-place of a bra. Certain advanced swimsuits for competitive athletes do not include any padding in the bust area, but are made out of thicker material, therefore preventing any accidental transparency.

Pro Tip: If you want to avoid your swimsuit being see-through, stay away from those without lining and suits that are pink/yellow. If you have an opportunity to try the suit on, be sure to apply water to areas you’re most concerned about being see-through

From a male perspective, most men’s swim trunks and shorts have additional lining and/or padding in the crotch area, which acts as a substitute for underwear. Usually, the lining is a mesh material with small holes. However, with technology advancements, more and more companies are making swim shorts and swim trunks without any lining. 

There is never a need to wear underwear beneath speedos (swim briefs); however, you can still be at risk of speedos being see-through.

Pro Tip: If you are at the store, stretch the suit material that doesn’t have lining and check if you can see anything through it. It is very rare that men’s swimsuits are see-through, but anything can happen, and no one wants to witness a wardrobe malfunction. Additionally, can always google swimsuit reviews to be safe

Is there any time I should wear underwear beneath my swimsuit?

In rare circumstances, yes. For example, if your swimsuit doesn’t have enough support, you can try wearing a bra underneath. If your swim shorts don’t have any lining, in most circumstances, it would probably be better to wear boxers or briefs rather than going commando. Females can wear panties with board shorts for additional comfort.

Some people may be simply afraid that their swim bottoms will fall down. Some just want extra support or compression – all valid reasons to wear underwear. However, most of these and similar problems can be eliminated by simply choosing a better swimsuit.

Can I just wear underwear as a swimsuit? What about a t-shirt?

Short answer – it depends. In general, it is not advised. Most swimming pools have some type of policy about swimwear usage. A majority of them require you to wear an acceptable swimsuit and prohibit wearing underwear or street clothing.

Those policies are mostly implemented for safety reasons. Clothes worn outside can transport waterborne disease and make other swimmers sick.

Clothing can also transfer dirt and dust particles into the pool, which can throw off the water chemical balance. Chemicals in the pool act as a disinfectant and help fight germs and prevent the spread of disease. Therefore, it is important to keep dirt from clothing away from the pool.

The rules are also needed to provide some consistency of coverage among swimmers, as well as avoid accidental nudity and unhappy customers. Because underwear usually doesn’t have a string to tighten it, the underwear is more likely to slide off your body while swimming. Underwear can also become see-through after getting wet.

At beaches, on the other hand, you can wear whatever you want, making it acceptable to wear bras, boxers, briefs, or anything else you can think of. I have been to some beaches that have regulations about swimwear, but those are very rare.

Pro Tip: If you forgot your swimsuit, you can wear a tight-fitting sports bra and nylon panties. I have even heard of men wearing tight women’s nylon underwear to pass as a speedo (this can be really embarrassing for some men, though). Just remember – underwear can become see-through after getting wet

Can I Wear a Swimsuit as An Undergarment?

Although a swimsuit can function as underwear, it is not recommended to use it in that way. Swimsuits can irritate skin and become uncomfortable over a long period of usage. Underwear is made specifically for prolonged wear and is constructed from breathable, moisture-absorbent materials that are pleasant to the touch and comfortable to wear. In addition, underwear is cheaper and will survive longer than a swimsuit worn as underwear.

To summarize, here are the reasons why you shouldn’t wear underwear under your swimsuit:

  • Underwear material is not made to be worn in the pool or any kind of water
  • It will be ruined by the chemicals in the swimming pool
  • It will absorb water, making it harder to swim
  • It will almost always be visible from underneath the swimsuit, which can look unpleasant and unattractive
  • It can be very uncomfortable
  • Underwear and street clothes can transport dirt and water-borne disease to the pool, harming other swimmers

Related Questions

Do professional swimmers wear any underwear beneath their swimsuits? Competitive swimmers never wear underwear under their swimsuits. Not only is it inconvenient, but it can also slow the swimmer down, and every hundredth of a second counts.

Are there swimsuits that can provide more coverage? You can purchase specific types of swimsuits that are more modest than regular swimsuits. There is a variety of swimwear that provides t-shirt, long-sleeve or even leg coverage. There are also Burqini and Alsharifa-style swimsuits for people with religious requirements, that cover entire bodies.

Do you wear underwear underneath your swimsuit? Have you ever? Let us know in the comments below!


Be sure to look into our other articles On Deck too!

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October 22, 2020 — Roman Trussov


M said:

I just bought a long leg white skin tight swimsuit for swimmers. It doesn’t have any lining but is very comfortable. It might be too see through when wet however.
What would you suggest as I swim laps at the YMCA 3x a week.

Lee said:

In the waterplay/splash pad i never wear briefs/undergarments under/with boardshorts.

In the waterpark/beach/river/pool etc. I often (80% of time) wear briefs/underwear with boardshorts especially when water is cold (below28*C) and i stay in the water for a long time.
It’s more comfortable.
It’s practical to wear undergarments with boardshorts for men but women don’t need to wear anything under 2 pieces swimsuits.
Undergarments for men are made for swimming and walking (water and air purpose) so undergarments for men are considered like a swimsuit.

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