If there’s one phrase every menstruating woman fears (other than ‘surprise pregnancy’!) it’s Toxic Shock Syndrome. TSS is something everyone has heard of, and no one actually understands; most of us just know it has something to do with tampons. So, while we can’t do anything about that unexpected pregnancy test result, we can tell you everything you need to know about toxic shock syndrome — what it is, what it isn’t, and how likely you are to get it.

What is Toxic Shock Syndrome?

Toxic Shock Syndrome is a complication from a bacterial infection, usually a staph infection, but sometimes strep. Specifically, staphylococcus aureus and group A streptococcus can both produce toxins that spread and cause inflammation throughout the body. This prompts the body’s immune system to go into hyper-drive, and the resulting flood of immune cells flood causes the body to go into shock. If it’s not stopped, organs can fail. It can be fatal; when it’s not fatal, it can have seriously debilitating long-term health consequences; in January, model-turned-TSS-activist Lauren Wasser had to have her remaining leg amputated as she continues to struggle with the fallout of TSS.

TSS can happen to anyone — man, woman or child; in fact, one-third of all TSS cases happen to men, according to Sara Chodosh reporting for Popular Science. People with a skin wound, burn or recent surgery are particularly at risk, as the wound can become infected and the broken skin offers toxins produced by the infection a direct route to your blood stream.

Then why is TSS linked with using tampons?

Tampons are, as Chodosh notes, “one of the few (or only?) foreign objects that we shove inside ourselves and let sit for many hours.” They’re basically just one giant opportunity for antigens to get inside and proliferate in the human body. Blood is, in fact, a culture medium in labs, and the warm, moist environment of the vagina is just what bacteria need to thrive — just ask the good, beneficial bacteria already teeming there. Most of the time, the immune system can fight off these burgeoning infections without a problem, but in the cases of the above strains, the toxins they produce are too, well, toxic for the body to handle.

Beyond the vagina’s natural bacteria-friendly environment, TSS is specifically linked with super-absorbent tampons — the most dangerous version of which originally contained carboxymethylcellulose (CMC) and hasn’t been manufactured since a TSS epidemic in the US in the 70s. While most of the tampons available in India look like they date from roughly that era, it’s unlikely they actually do. Still, even modern, non-CMC super-absorbent tampons are a concern, when it comes to TSS, for two reasons: One, they are designed to stay inside the body for long periods of time, allowing bacteria plenty of time to proliferate; and two, their super-absorbent nature can dry the vagina, leaving scratches on the vaginal walls that allow toxins easier access to your blood stream. (This latter problem is a concern for any size of tampon, if it’s designed for a heavier flow than you’re currently having.)

How likely are you to get TSS from tampons?

Very unlikely, despite what seeing the warning on every tampon box may make you think. Toxic shock syndrome is really, really rare — in 2016, the US recorded only 323 cases, less than half of which were due to tampon use. Good hygiene, making sure your tampon size matches your flow, and following directions, which typically advise removing a tampon after four to eight hours, go a long way to preventing toxic shock syndrome.

Organic, all-cotton tampons  are a new trend in menstrual products, and have been suggested as a safer alternative with less-to-no TSS risk. But the few studies into organic tampons and TSS risk are conflicting. It’s likely they carry similar risks to menstrual products like sponges and cups, which technically can cause TSS, but are associated with few cases.

What are TSS symptoms? And what do you do if you think you have it?

Toxic shock syndrome is possible, even if it’s rare. So it’s good to be aware of the signs of TSS — which unfortunately mimic those of the flu, but come on much more rapidly.

• A sudden high fever
• Low blood pressure (hypotension)
• Vomiting or diarrhea
• A rash resembling a sunburn, particularly on your palms and soles
• Confusion
• Muscle aches
• Redness of your eyes, mouth and throat
• Seizures
• Headaches

If you’ve recently used a tampon, had surgery or suffered a skin wound and experience any one of these symptoms, call your doctor immediately. In most cases, TSS can be combated with modern antibiotics, but timely treatment is of the essence for this fast-acting condition.

TSS is a very serious, but very unlikely condition. If tampons were never your cup of tea, then you don’t need to worry about toxic shock syndrome. And if tampons are your menstrual product of choice, you still don’t really need to worry; just follow directions and avoid the super-absorbent kind.