“There is a learning curve. It takes some time and getting familiar with your body. And I think it’s very important for people who want to use the cup to be prepared for that.”

New users are often shocked at the size of the devices. Menstrual cups hold just less than one fluid ounce. They come in different sizes, but all are about 1.9 inches high. The rim of the cup, or bell, is about 1.6 inches in diameter.

[Read The Wirecutter’s review of menstrual cups.]

“People don’t understand their anatomy — they see it and think, ‘It will never fit,’” said Penelope Phillips-Howard, the review’s senior author, also of the Liverpool School of Tropical Medicine. “They don’t realize that actually it’s very flexible. You shape the cup in a certain way in position and fold it so you can insert it, and then it opens up inside the vagina.”

If the cup is inserted incorrectly, it will be uncomfortable, and the user should remove it and try to reinsert it, Dr. Phillips-Howard said. It can take two to three months for a woman to become accustomed to the device. (Her own research has found that teenage girls in Kenya preferred menstrual cups to pads.)

And, she said, there is an initial ‘ick’ factor that needs to be overcome.

“This is just anecdotal, but many girls and women I’ve spoken to say it’s a bit yucky,” Dr. Phillips-Howard said. “Menstrual blood is taboo. It’s not to be seen, not to be talked about. And some people don’t like to touch their bodies. You have to be willing to touch yourself, though it’s not very different from using a tampon.”

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The new analysis found no increased risk of infection associated with the use of menstrual cups. But the authors identified five cases in which menstrual cup users developed toxic shock syndrome, a life-threatening condition caused by the release of toxins from the overgrowth of Staphylococcus aureus bacteria.

Since the total number of menstrual cup users is unknown, however, the authors were not able to estimate the risk compared to other menstrual products, such as high-absorbency tampons, which were once linked to toxic shock syndrome.