Cruises are supposed to be all about sun, fun, and relaxation. But on Reddit recently, a very different topic grabbed attention: where passengers stash their SeaPass cards.One traveler on Independence of the Seas — a ship under the Royal Caribbean umbrella — posted that they twice saw women pull their cards from inside their bras.FLIGHT PASSENGER GETS TOO COMFORTABLE ON PLANE, SPARKING ETIQUETTE DEBATE"Frankly disgusting," the poster declared. "Please just buy a lanyard."For the uninitiated, a SeaPass is Royal Caribbean’s onboard ID and payment card. It opens your stateroom door, acts as your charge card for drinks and shopping, and is used for getting on and off the ship. In short, it’s the one thing you absolutely can’t cruise without.The thread drew hundreds of comments, with travelers weighing in on whether this habit is gross, practical, or simply inevitable.Some sided with the original complaint. 5 DIRTIEST SPOTS IN HOTEL ROOMS: WHAT EXPERTS SAY TO DO AT CHECK-IN"As someone who worked retail…Sweat, lots and lots of sweat. Nothing worse than being [handed] damp money," one commenter wrote.But plenty pushed back. "I hate to break it to you, but cash is wayyyy dirtier than a key card stored in a bra." one person argued. TSA REVEALS THE SURPRISING REASON PEOPLE MIGHT SET OFF SECURITY ALARMS DURING SCREENINGAnother noted, "People do not wash their hands so often that cruise ships have to almost beg them to before visiting the buffet. Boob sweat is the very least of your worries."Many pointed out that women’s clothing often lacks usable pockets, leaving bras as one of the few reliable options. "If I had a pocket, it would go in there," wrote one commenter. "Until then…[my bra reigns] supreme."Other users suggested phone cases with card slots as an alternative to lanyards.CLICK HERE TO SIGN UP FOR OUR LIFESTYLE NEWSLETTERHealth experts note that skin itself isn’t inherently dirty, but damp areas can harbor bacteria and yeast. The American Society for Microbiology has shown that warm, moist skin folds are more likely to collect microbes. MORE IN LIFESTYLE NEWSThat doesn’t mean a SeaPass card from a bra poses a major health risk, but it helps explain why some passengers find the practice unappealing.Fox News Digital reached out to Royal Caribbean for comment.