Let's face it: As wonderful as hot tubs feel, they can get pretty gross. Razyph / Via gettyimages.com Hot tubs or jacuzzis are a great way to soak and relax, especially when it's super chilly outside in the winter. But hot tubs are also known to carry a ton of germs and transmit water-borne diseases, and it's a bit of a problem in the US. In May, the CDC published the results of a 2013 survey involving about 49,000 public aquatic venues. It found that one in eight inspections resulted in immediate closure due to serious health violations. We reached out to Dr. Pritish Tosh, infectious disease specialist at the Mayo Clinic in Rochester, Minnesota, and germ expert Kelly Reynolds, PhD, director of environmental health sciences at the University of Arizona, to find out why hot tubs get so contaminated and how they can make you sick, so that you can be more careful and stay healthy. 1. A lot of germs and pathogens survive in hot tubs. Peshkova / Getty Images / Via gettyimages.com When you get in a hot tub, everything on your body ends up in the hot tub, too— including sweat, dirt, oil, grime, bodily fluids. A lot of this stuff is harmless, but a surprising number of people carry pathogens, or germs that cause disease. "People are colonized with infectious bacteria on their body, meaning it doesn't harm them but it can make other people very sick," says Tosh. Examples of bacteria carried on the skin include Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), and Pseudomonas. People can also shed gastrointestinal pathogens from their feces, such as E. Coli, Shigella, Vibrio, Norovirus, and Cryptosporidium. Even the herpes virus can survive in hot tubs for up to four hours. The list of germs that love to hang out in hot tubs is unfortunately — and horrendously — long. 2. The temperature of hot tubs is actually perfect for bacteria to grow. Tap to play or pause GIF Tap to play or pause GIF Tap to play or pause GIF Tap to play or pause GIF University of California Berkeley / Via ucresearch.tumblr.com Hot tubs are usually kept between 100 and 105 degrees fahrenheit, the experts say. That might feel scalding on your skin if you jump in after swimming in a cold pool or being in the cold and snow, but don't be fooled. The temperature of hot tub water is definitely not high enough to kill bacteria and other germs. The warm, wet environment actually fosters bacterial growth and survival. "Germs are perfectly happy living at those temperatures and can survive for days, even weeks," says Reynolds. 3. Hot tubs are like a big bath where everyone gets a turn to sit in the same hot water. Tap to play or pause GIF Tap to play or pause GIF Tap to play or pause GIF Tap to play or pause GIF FOX / Via simpsonsworld.com Think about how small a hot tub is compared to an olympic-sized swimming pool. You can still transmit bacterial infections and viruses in large pools, even though the pathogens and fecal matter have more space to live. So if the same amount of germs are in a hot tub, the water is way more concentrated, and the risk of infection is even higher, experts say. "Hot tubs are very problematic for this reason — a small volume of water filled with bodies makes the chlorine demand impossibly high," Reynolds says. One person can contaminate the entire hot tub by only shedding a small amount of feces (more on fecal shedding and how it happens shortly). Basically, soaking in a dirty hot tub is kind of the same thing as taking an intimate bath with whoever else used the hot tub. 4. Hot tubs are very difficult to keep clean and chlorinated. StefanieDegner / Via gettyimages.com Sure, you can use disinfectants to kill the germs in a hot tub, but there's a catch: The heat actually breaks down these cleaning chemicals faster, so you need to replace them more often. The CDC recommends checking and adjusting your hot tub chemicals every hour when it's in heavy use to make sure the chlorine is 2-4 ppm, the bromine is 4-6 ppm, and pH level is 7.2-7.8. Not to mention you should regularly scrub off the slimy bacteria biofilm that tends to coat hot tubs.More importantly, most people are not this crazy strict about cleaning. Ideally, Reynolds says you would adjust the chlorine in a hot tub after every single use and replace or clean your filter frequently, but this usually doesn't happen. The bottom line: Hot tubs are high maintenance and require a lot of knowledge and care to stay clean. 5. And chlorine gets depleted by things like sweat, sunscreen, and skin or hair products. paultarasenko / Via gettyimages.com Unless you rinse off before you get in a hot tub, you'll bring everything that's on your body into the water. “The sweat and sunscreen, shampoo, or conditioner will use up and remove the chlorine from the water, so there’s a lower concentration than there needs to be to kill all the bad bacteria,” Reynolds says. The more people and the longer you sit in the hot tub, the more rapidly disinfectant levels decrease, she says. Not to mention, skin cells and residual urine from the body can also interact with chlorine to produce chloramines, which irritate your eyes, skin, and respiratory tract. Unfortunately, the experts say that most people in America don't shower before they get in hot tubs or pools, even though it's standard practice in Europe. 6. Hot tubs can cause a nasty rash called hot tub folliculitis. Doc James / Wikimedia Commons / Via commons.wikimedia.org Hot tub folliculitis is an unfortunately common consequence of soaking in contaminated hot tubs. It's a head-to-toe rash caused by Pseudomonas aeruginosa bacteria, which infects the hair follicles, says Tosh. The rash looks like the chicken pox and it's very uncomfortable. "It's very difficult to treat so you really just have to wait for it to go away but it can cause scarring for life," Reynolds says. Pseudomonas aeruginosa is found naturally in water, Reynolds says, but it grows readily in the warm aereted (bubbly) water of a hot tub. Chlorine can kill Pseudomonas bacteria but only if the concentration is high enough. "It also forms a protective biofilm on the filters, making it very hard to control," she says. 7. They carry bacteria which can cause ingrown hairs and small cuts to become infected. Pobladurafcg / Getty Images / Via thinkstockphotos.com About 50% of the population carries Staphylococcus aureus on their skin. And yes, enough chlorine will kill the Staph, but most hot tubs aren't properly chlorinated. If someone gets into a contaminated hot tub with a cut, ingrown hair, or any other open wound where the water can enter — they can easily contract a bad staph infection, which requires further treatment, Tosh says. It's less common, but MRSA can also survive in hot tubs — this antibiotic resistant bacteria can cause potentially fatal skin infections. So besides keeping your hot tub chlorinated and clean, you should probably stay out if you have any wounds where bacteria can enter. 8. There's a lot of poop in hot tubs. Karam Miri / Via gettyimages.com Before we give you the facts, remember that poop is everywhere — including our smartphones — so don't panic when you read these statistics. "Five people in a hot tub naturally contribute about a tablespoon of feces to the tub from residual fecal matter on the skin," Reynolds says. In a typical busy public pool or water park, there are several pounds of feces shed in the pool by the end of the day, she says. That's a lot of shit to deal with.The truth is that we all have residual feces on our bodies, Reynolds says, unless we’re literally soaping up every time we use the bathroom or a bidet. Adults shed an average of 0.14 grams of feces, which is equivalent to the weight of one pea, and kids can carry up to 100 times that amount. This is why it's so important to keep your hot tub clean, because if the fecal matter builds up or it contains any bacteria from a sick person, it can cause problems. 9. You're supposed to wait two weeks after having diarrhea to go in a hot tub, but most people don't — which exposes others to gastrointestinal bacteria. Ablemark / Via gettyimages.com Seriously, do not get in a hot tub or pool after you've had a diarrheal disease or gastrointestinal infection, Tosh says. The CDC suggests you wait two weeks because that's how long it takes your body to fully recover and stop shedding diarrhea-causing pathogens, which can make other people sick if they swallow water. “Even if you feel better and you don’t have symptoms, you can still be shedding millions, even billions, of diarrhea germs,” Reynolds says. Unfortunately, not many people know about this rule or understand the risks of leaking a little diarrhea into the hot tub. So if you aren't entirely sure about how clean a hot tub is, definitely keep your head above the water and don’t open your mouth underwater... ever. 10. A common hot tub parasite, Crypto, is chlorine-tolerant. CDC / Via cdc.gov Cryptosporidium is a parasite that causes severe diarrhea lasting for weeks; and there’s no cure or antibiotic, so you just have to wait it out. “Crypto is easily passed through feces and it causes most recreational water illness outbreaks, and even a few deaths, each year,” Reynolds says. Crypto is especially bad because it’s chlorine-tolerant, so it'll withstand your typical chemicals for days before dying off. The parasite stays in your feces for days or even weeks after you get sick and even when you get better, says Tosh. So the people who bring it into hot tubs probably aren’t even aware — and it takes only a little bit of feces to contaminate the whole hot tub with Crypto. The only good news is that Crypto is spread through the fecal-oral route, and you're less likely to accidentally swallow water in a hot tub than you are in a pool. 11. It's rare, but hot tubs can also transmit Legionnaires' disease, a potentially fatal respiratory disease. Jarun011 / Via gettyimages.com Legionnaires' isn't as common as the other hot tub infections we've mentioned, but it's definitely still a concern. It's caused by the Legionella bacteria, which thrive in warm water that isn't properly cleaned. You can only get infected by breathing in the mist and steam from a contaminated hot tub, says Reynolds, and it causes an upper respiratory infection similar to pneumonia. According to the CDC, each year 8,000 to 18,000 people in the US are hospitalized with Legionnaire's but people who are over 65, immunosuppressed, or smoke are at higher risk. If you don't get the proper antibiotic treatment, it can kill you. You can avoid Legionella by keeping the chlorine, bromine, and pH levels high. Also, you can't tell if your hot tub has Legionnaires' until someone gets sick, Reynolds says, so it's a good reason to be super careful with the chemicals. 12. Bacteria will grow overnight if the hot tub isn't cleaned beforehand. pastorscott / Via gettyimages.com One of the most important practices is adding enough chlorine before finishing up for the night, Reynolds says. If you don't, the hot tub water will spend hours and hours just sitting still at a high temperature, allowing the chlorine and bromine to continue to break down and more bacteria to grow. Since you probably aren't adding chlorine every few hours throughout the night, it's important to try to "shock" the water with a very high amount before you cover it up for the night. 13. Private hot tubs actually tend to be worse than public ones. Tap to play or pause GIF Tap to play or pause GIF Tap to play or pause GIF Tap to play or pause GIF FOX / Via giphy.com Okay, hear us out. At a public hot tub or spa, there's a lifeguard or staff whose job it is to routinely check the chlorine levels and adjust accordingly. There are also more rules at public hot tubs to keep it clean, such as showering before entering or not allowing children in — they do, after all, shed the majority of fecal matter and germs. "Private hot tubs are often worse because it's up to the owner to be diligent about cleaning and people get lazy when it's only family and friends using the tub," says Reynolds. And it doesn't matter whether it's your spouse who is in the hot tub with you or a complete stranger, because either way you can't tell if another person is shedding infectious pathogens or viruses. Bottom line: Keep your hot tub clean!