There are some things that are surprisingly easy to forget: Mom’s birthday (is it the 21st or the 23rd?!), turning off the oven after making banana bread, putting on deodorant, and yes, changing your tampon. People, it happens to the best of us, which is why you might find yourself wondering, really, how long can you leave a tampon in?

Most likely if you forget to change your tampon at regular intervals once in a while, it’s NBD. But if you have a light flow and don’t want to bother changing your tampon, docs say you should think twice about ignoring the instructions on the box to change it every few hours, since tampon ingredients aren’t meant to stay inside you forever.

There are indeed some important tampon safety tips that you should follow to avoid risks of prolonged use.

How long can you leave a tampon in?

Most gynecologists say you shouldn’t leave one in for more than eight hours at a time. Why? Because while tampons these days are generally very safe, leaving a tampon in for too long can alter the pH of the vagina, which allows bacteria and fungi that are already living in your vagina to grow.

“Yeast and bacteria tend to thrive in moist places, with blood as a medium,” says Alyssa Dweck, MD, FACOG, a gynecologist in New York who has been voted top doctor in New York magazine and in Westchester County. Similarly, while it is safe to pee and poop with a tampon in, you may want to change out for a new one if the string gets exposed to stool (and thereby, bacteria), or if the tampon gets slightly dislodged from straining.

Can you sleep with a tampon in?

Generally, yes, says Dr. Dweck. But if you’re regularly sleeping longer than eight hours at a time (lucky you), you might want to initiate a changing of the guard.

“Most people have the question if they can wear a tampon overnight when they’re sleeping,” Dr. Dweck says. “You can, but if you’re a 12-hour sleeper you should plan accordingly.”

How long can you leave a tampon in after swimming?

According to Penn Medicine, water does not enter the vagina when you go swimming. When swimming while wearing a tampon, change your tampon at the time you normally would.

Potential tampon health hazards if you leave it in for too long

The longer a tampon is left in, the more likely it is to throw the natural balance of bacteria and yeast out of whack. Here’s what can happen if you let a tampon overstay its welcome.

Bacterial and yeast infections

Over time, forgetting to change a tampon increases the risk of irritation and infections, including bacterial vaginosis (BV) and yeast infections, explains Jessica Shepherd, MD, FACOG, a former assistant professor of clinical obstetrics and gynecology at the University of Illinois College of Medicine, in Chicago and current chief medical officer of Verywell Health. You may notice a strong odor that can get quite foul (musty or fishy) due to the blood, secretions, and bacteria in the tampon, and vaginal discharge may appear brownish red or thick yellow, says Dr. Shepherd.

Because tampons are highly absorbent, Dr. Dweck adds that they wick moisture out of the vagina the longer they’re in, making tissue dry and irritated. And if you’re particularly susceptible to yeast infections, she suggests being extra careful about regularly changing your tampon and avoiding scented tampons, which can alter the pH of the vagina and increase infection risk.

The 411 on toxic shock syndrome

Yet another key reason to change your tampon on the reg: In very, very rare circumstances, an overgrowth of certain types of bacteria, including Staphylococcus aureus (staph) and group A streptococcus (strep), can enter the bloodstream through tiny tears in the vagina and cause toxic shock syndrome (TSS). The higher absorbency of the tampon, the greater the risk—which is why doctors recommend using the lightest absorbency that handles your flow and changing tampons regularly. “[TSS] can progress very quickly and cause multi organ failure and damage,” says Dr. Dweck.

According to the Centers for Disease Control and Prevention (CDC), TSS got on our collective radars following an increase in TSS cases and deaths of healthy young American women between 1979 and 1980. The FDA began requiring tampon manufacturers to reduce the levels of certain chemicals (dioxins and rayon) used in tampons to minimize the absorbency to a safer level. Manufacturers also began adding instructions on the label advising women to change tampons frequently. By 1986, TSS cases had dropped significantly. Nowadays, TSS happens but is rare: Dr. Dweck says that she’s only seen TSS two or three times in her more than 20 years of practice, none of which were severe enough to cause death. (Nationally, rates are estimated to be about one to three cases per 100,000 people each year.)

For the record, you should be sure to regularly change your menstrual cup if you use one, too: That same moist environment can similarly lead to infections, including TSS.

Other potential tampon health hazards

Tampons can expire and potentially grow mold. To avoid infections, make sure you purchased your tampon stash within the last five years. If that sounds expensive, explore these resources for free tampons.

If your tampons are current, the ingredients that make up tampons are generally very safe. Titanium dioxide in tampons has caused a stir in recent years thanks to some studies done on animals that saw adverse effects when they ingested this common whitening agent. But there isn’t evidence one way or the other that it’s harmful to humans when used in a tampon.

Finally, tampons should not cause you to feel pain. If you associate tampons and cramps with each other, that’s probably a coincidence. Pain from a tampon could mean you’ve inserted the tampon incorrectly, but it could also be a sign of something bigger going on. So speak with your doctor if tampons cause you to experience pain.

What to do after leaving in a tampon for too long

First of all, try not to freak out. Most of the time if you leave a tampon in for more than eight hours, you’ll just need to remove it and remind yourself to be more careful.

If you’re wondering “should I see a doctor?” about extended tampon use, the answer is definitely yes if you exhibit any TSS symptoms. Those include unusual abdominal pain or pressure, a skin rash (which looks like a bad sunburn or red dots), or flu-like symptoms including a high fever, chills, and watery diarrhea. “Believe me, if it’s TSS you’ll be in the ER. It’s unusual to miss the symptoms,” says Dr. Dweck.

Also check in with your doctor if you have symptoms of BV or yeast infections, which include a change in vaginal discharge (BV tends to be grayish-white and foul-smelling, while yeast infections cause thick, white discharge), vaginal itching or irritation, pain during sex, painful urination, and vaginal spotting outside of your period.

“I don’t want to give tampons a bad name. Loads of women use them and there’s really no problem with them. You just have to be smart about it,” says Dr. Dweck. Hear, hear.