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When you hear about the dangers of toxic shock syndrome (TSS), the conversation typically focuses on the risk of leaving a tampon in for too long. While that can up your chances of getting TSS, using the appropriate size tampon according to your current flow is equally important—a fact that one North Carolina woman learned after she nearly died from TSS as a result of wearing and removing a super-absorbent tampon during a light-flow day.

Earlier this year, Greta Zarate, a 32-year-old mother of five, experienced flu-like symptoms on the day she started her period, Fox News reports. But after treating her symptoms with over-the-counter medication and spending a few days in bed, Zarate realized she was only getting “sicker and sicker.”

Zarate then went to the hospital, where she learned her blood pressure was extremely low and her spleen was enlarged, as her body was attempting to fight off an infection.

She was diagnosed with TSS, which had developed after she removed a super-absorbent tampon when her period flow was light, resulting in microscopic cuts on her vaginal walls that allowed bacteria to enter her body and cause an infection, according to Fox News.

Zarate said she knew that leaving a tampon in for too long could potentially lead to TSS. “[But] I never knew that the size of the tampon should move with your flow,” she told SWNS, per Fox News. After 11 days in the hospital—including four days in intensive care—Zarate was treated with a blood transfusion and a round of antibiotics.

Fortunately, she made a full recovery, but this illustrates that tampon sizes remain a less commonly known cause of TSS, especially as the mortality rate for TSS has continued to drop, says Yvonne Bohn, M.D., an ob-gyn and chief medical correspondent for Cystex. Here’s a breakdown of the relationship between TSS and tampon size.

What is toxic shock syndrome?

TSS is a clinical illness—typically caused by the bacteria staphylococcus aureus (commonly known as staph)—that can result in a high fever, fainting, a flat red rash on the skin that looks like a sunburn, very low blood pressure (called hypotension), and potential failure of multiple organs, explains Dr. Bohn. Long-term complications include liver or kidney failure, and at its most extreme, TSS can lead to amputation of fingers, toes, or limbs, and even death, she adds.

Though young women most commonly experience TSS, anyone is at risk (including men and children), because we all carry the staph bacteria that produce the toxins that can lead to infection, says Dr. Bohn.

TSS can usually be diagnosed based on clinical signs (like the presence of a rash or a significantly low blood pressure reading), laboratory evidence of liver or kidney failure, or by finding cultures that have traces of staph bacteria, adds Dr. Bohn, who notes that TSS can come on very suddenly and requires immediate medical attention.

What are the causes of TSS?

Toxic shock syndrome is most commonly associated with wearing a tampon for too long—but that doesn’t characterize all cases of TSS, says Dr. Bohn. “About 50 percent of cases are associated with menstruation, but [the other] 50 percent are associated with non-menstrual conditions such as post-surgical wound infections, postpartum wound infections, burns, and respiratory infections.”

In other words, anyone who has recently undergone surgery and/or suffered a wound infection can be at risk for contracting TSS.

Changes in tampon sizes and formulation helped reduce the risk over time, she says. However, while it is rare to contract TSS, it’s not impossible, adds Dr. Bohn.

How can the wrong tampon size lead to TSS?

If you use tampons and are afraid of getting TSS, don’t fret. Tampons are safe to use—but you have to change them often and use the proper size according to your current flow, says Dr. Bohn.

The benefit of using a smaller tampon is that you will naturally have to change it more frequently, whereas you might falsely assume you can leave a larger tampon in for longer periods of time, which may then up your chances that bacteria will grow on the tampon and enter your bloodstream, explains Dr. Bohn.

Note: Even on days when your period flow feels light, and it seems like your tampon doesn’t need to be changed as frequently because the blood isn’t soaking through, you should still change it with the same frequency, just to be safe, says Dr. Bohn. As long as you’re wearing a tampon size that matches your flow, you should be able to avoid scraping the inside of the vaginal wall when removing the tampon, she explains.

If you’re not sure whether your flow is heavy enough at all for a tampon, play it super safe and stick to a pad or menstrual cup.

If you feel discomfort or pain when inserting a tampon, that might be a clue that you’re using one that’s too large for your period flow. And if it feels painful to insert any tampon, regardless of size, Dr. Bohn recommends consulting your doctor, who can look for hormonal changes (which can happen after childbirth, during breastfeeding, or before menopause), cervical inflammation, endometriosis, or any other infection or pain disorder, all of which can lead to vaginal dryness and could explain the discomfort, explains Dr. Bohn.

How serious is TSS, and how is it treated?

TSS can be very serious—and fatal, if not treated quickly, says Dr. Bohn.

Once you’ve received a proper diagnosis, doctors will work to “reverse hypotension and shock” by way of antibiotics and by treating any “suspected wound infections,” explains Dr. Bohn. “It’s also important to prioritize the removal of any foreign bodies like tampons or [similar] wound-packing materials,” she adds.

How can you prevent TSS?

Dr. Bohn warns that those who have had TSS should never use tampons—period. Unfortunately, reinfection is “common” in those who have already had TSS, according to Johns Hopkins Medicine.

For those who’ve never had TSS, Dr. Bohn recommends changing tampons “about every three hours,” noting that all women should not sleep in tampons.

As for the size of your tampon, it should always match your flow, says Dr. Bohn.