A menstrual cup is a flexible cup or barrier worn inside the vagina during menstruation to collect menstrual fluid. Unlike tampons and pads, the cup collects menstrual fluid rather than absorbing it. They are usually made from medical grade silicone.
An early version of a bell-shaped menstrual cup was patented in 1932. Later menstrual cups were patented in 1935, 1937, and 1950. The Tassaway brand of menstrual cups was introduced in the 1960s, but it was not a commercial success. Early menstrual cups were made of rubber. Today, both silicone and rubber models are available. Most are reusable, though there is at least one brand of disposable menstrual cups currently manufactured.
In 1987, another latex rubber menstrual cup, The Keeper, was manufactured in the United States. This proved to be the first commercially viable menstrual cup and it is still in manufacture today. The first silicone menstrual cup was the UK-manufactured Mooncup. Most menstrual cups are now manufactured from medical silicone because of its durability and hypoallergenic properties. The German brand MeLuna is the only company to manufacture their cup out of TPE (thermoplastic elastomer). Menstrual cups are becoming more popular worldwide, with many different brands on the market, and there are different sizes and shapes available.
There are two types of menstrual cups currently available:
The first type is a bell-shaped cup made of rubber (latex), silicone or thermoplastic elastomer (TPE). It is reusable and designed to last for up to 10 years. Some brands recommend replacement each year, as it is a hygiene product. Other brands recommend replacement after 5–10 years, stating that women have been comfortable using them up to 10 years. These bell-shaped silicone or rubber cups must be removed before penetrative vaginal sex.
The second type is made of polyethylene and resembles the shape of a contraceptive diaphragm. There are two types of polyethylene softcups: a disposable version designed for disposal after one use, and a reusable version, designed for re-use for one menstrual cycle. These polyethylene cups may be worn during intercourse, though they are not contraceptive devices.
Most brands have a smaller and a larger size. The smaller size is normally recommended for women under 30 who have not given birth vaginally, or for a lighter flow. The larger size is normally recommended for women over 30, who have given birth vaginally, or who have a heavier flow. The menstrual cups with the smallest size diameter are recommended for teenagers, as well as women who are more physically fit, as those with stronger pelvic floor muscles may find a larger cup slightly uncomfortable. Some brands have a different "squishiness" than others. Shape is also important, as women vary in shape preferences for comfort. As well as shape and width, length also needs to be considered, for example if a woman's cervix sits particularly low, they may need to consider a shorter length cup. Capacity is important to women who have a heavier flow; however, all of the menstrual cups currently available have higher capacity than a regular tampon.
The menstrual cup is first folded, and then inserted into the vagina. It will normally unfold automatically and create a light seal against the vaginal walls. In some cases, a woman may need to twist the cup or flex her vaginal muscles to ensure the cup is fully open. In most women, a menstrual cup will sit lower in the vagina than a tampon. If correctly inserted, the cup shouldn't leak or cause any discomfort, as with a tampon. Those who are familiar with inserting a non-applicator tampon should learn faster how to insert a cup, though there is still a learning curve. If lubrication is necessary for insertion, it should be water-based, as some lubricant ingredients can be damaging to the silicone. After up to 12 hours of use (less if the cup starts to overflow), the cup is removed by reaching up to the stem of the cup in order to find the base. The stem cannot be used to remove the cup, as pulling it down will create suction. The base of the cup is pinched to release the seal, and the cup is removed. After emptying, the cup should be rinsed or wiped and reinserted. It can be washed with a mild soap, and sterilized in boiling water for a few minutes at the end of the cycle.
One case report in the journal Gynecologic and Obstetric Investigation noted the development of endometriosis and adenomyosis in one menstrual cup user.  However, the U.S. Food and Drug Administration declined to remove menstrual cups from the market, saying that there was insufficient evidence of risk.
A 2011 randomized controlled trial in Canada measured urovaginal infection in a comparison of menstrual cup and tampon use, and found no significant difference in physician-diagnosed urovaginal symptoms between the 2 groups. The Journal of Women's Health has published a clinical study demonstrating the acceptability and safety of the Instead Softcup in both clinical and pre-clinical testing. Generally, menstrual cups do not significantly affect the population of vaginal flora, including the bacteria responsible for bacterial vaginosis (including yeast infections) or urinary tract infections. There have been no reported cases of toxic shock syndrome (TSS) occurring with the use of menstrual cups.
Acceptability studies 
A 2011 randomized trial in Canada investigated whether menstrual cups are a viable alternative to tampons and found that approximately 91% of women in the menstrual cup group said they would continue to use the cup and recommend it to others. In a 1995 clinical study involving 51 women, 23 of the participants (45%) found menstrual cups to be an acceptable way of managing menstrual flow. In clinical testing, after three cycles of softcup use, 37% of subjects rated the softcup as better than, 29% as worse than, and 34% as equal to pads or tampons. The 37% who preferred the softcup attributed their preference to "comfort, dryness, and less odor."
- Most menstrual cups are made from medical grade silicone, which is a safe, easily cleaned, and hypoallergenic material. TPE has the same advantages as silicone and the additional qualities of being somewhat softer and less expensive. The other material sometimes used for cups is latex, which is equally safe for people who are not allergic to it.
- Reusable menstrual cups are more cost-efficient than disposable sanitary napkins and tampons, as they can be used for up to 5 years.
- Since they are reusable, menstrual cups also help to reduce waste. Disposable sanitary napkins and plastic tampon applicators can remain in landfills for hundreds of years because they are not easily biodegradable.
- Compared to other reusable feminine hygiene products (cloth menstrual pads, reusable tampon-style options like sea sponges) menstrual cups are easier to clean and sterilize after use and typically last longer.
- Menstrual cups can be used when swimming or playing sports the way tampons can.
- Many users, and some gynecologists, believe that menstrual cups are gentler on the vaginal environment than tampons. Tampons absorb all moisture in the vagina, including healthy fluids that are necessary to protect the vaginal walls and maintain the correct pH level and beneficial bacteria populations. Because they collect, rather than absorb menstrual fluid, menstrual cups affect the fluid balance of the vagina less than tampons. In addition, most mass-produced tampons contain rayon fibers, which can separate, stay in the vagina, and collect bacteria. The bleaching process many tampons undergo can also produce trace amounts of dioxin, a suspected carcinogen, although the FDA considers the levels of dioxin in tampons safe. In any case, menstrual cup use is not associated with Toxic Shock Syndrome, an infection that can often be traced to improper tampon use.
- Cups have a greater capacity than pads and tampons, and can be left in the vagina for up to 12 hours if not full, unlike pads and tampons which require more frequent changing. On moderate and light flow days, a woman need only insert the cup and clean and empty it at the end of the day rather than carrying several replacement pads or tampons.
- By keeping menstrual fluid away from the vaginal walls and vulva and unexposed to air, menstrual cups have less odor associated with their use than pads.
- When using a menstrual cup, the menstrual fluid is collected away from the cervix and held in liquid form as opposed to it being absorbed and held in semi-coagulated form against the cervix as is the case with tampons.
- Since menstrual cups collect menstrual fluid inside the vagina and do not leak (if emptied often enough) the way tampons do, there is less break through bleeding and wetness during use.
- If a woman needs to note how much menstrual fluid she is expelling for medical reasons, a cup can allow her to tell more accurately. Some cups even have measuring marks on them.
- Some women find that they bleed less or have shorter periods when using a menstrual cup as opposed to tampons. This may be because the absorbency of tampons can draw menstrual fluid out of the uterus.
- Individual menstrual cups are noticeably more expensive than a package of sanitary napkins or tampons, so that, while in the long run using a menstrual cup saves women money, it requires some upfront investment.
- Some women experience difficulty in inserting or removing the menstrual cup depending on certain physical factors. Remedies for this include selecting a different size, shape, or material cup, using a water-based lubricant to ease insertion, changing the folding method for insertion, and practice.
- Use of a menstrual cup results in closer contact with a greater volume of menstrual fluid than traditional women's hygiene products, which may be discomfiting.
- Some women find menstrual cups uncomfortable initially. This may lessen with practice inserting the cup, selecting a more appropriately sized or shaped cup, and/or trimming the stem of the cup, if present.
- Cleaning the cup after emptying it can pose complications in crowded public restrooms and places without potable water. Carrying a small bottle of water or simply wiping the cup with durable toilet tissue can suffice if running water is not immediately available.
- There have been rare cases in which women using IUDs for birth control inadvertently dislodged the IUDs when removing their menstrual cups. Women with IUDs who are considering using cups should consult with their gynecologists.
- Use of a menstrual cup can stretch or break the hymen, arguably even more than tampon use. Since some cultures value preservation of the hymen as evidence of virginity this can discourage young women in those cultures from using cups.
- Women with pelvic organ prolapse may not be able to use menstrual cups comfortably or safely.
See also 
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- Goddard, L.J. US Patent #1,891,761 (issued December 1932).
- Hagedora, Arthur F. US Patent #1,996,242 (issued April 1935).
- Chalmers, Leona. US Patent #2,089,113 (issued August 1937).
- Chalmers, Ileona W. US Patent #2,534,900 (issued December 1950).
- Wysocki, Susan. "New Options in Menstrual Protection". Advance for Nurse Practicioners (November 1997).
- Pruthi, Sandhya. "Menstrual cup: What is it?" Mayoclinic.com (January 30, 2008).
- "Alternative Menstrual Products". Center for Young Women's Health. Boston Children's Hospital. 28 March 2013. Retrieved 30 March 2013.
- LeVay, Simon & Sharon M. Valente. Human Sexuality. Sinauer Associates (2002), p. 104. ISBN 0-87893-454-5.
- "Assorted Size Charts". Menstrual Cup Support. 18 August 2008. Retrieved 8 November 2009.
- Stewart, Elizabeth B. The V Book: A Doctor's Guide to Complete Vulvovaginal Health. Bantam (2002), p. 96. ISBN 0-553-38114-8.
- Spechler S, Nieman LK, Premkumar A, Stratton P (2003). "The Keeper, a menstrual collection device, as a potential cause of endometriosis and adenomyosis". Gynecologic and Obstetric Investigation 56 (1): 35–7. doi:10.1159/000072329. PMID 12867766.
- Lione, Armand. "Citizen Petition on Menstrual Cups & Endometriosis". Retrieved 19 December 2010.
- Howard C, Rose CL, Trouton K, Stamm H, Marentette D, Kirkpatrick N, Karalic S, Fernandez R, Paget J (June 2011). "FLOW (finding lasting options for women): Multicentre randomized controlled trial comparing tampons with menstrual cups". Canadian Family Physician 57 (6): e208–15.
- North BB, Oldham MJ (February 2011). "Preclinical, Clinical, and Over-the-Counter Postmarketing Experience with a New Vaginal Cup: Menstrual Collection". Journal of Women's Health 20 (2): 303–311. doi:10.1089/jwh.2009.1929.
- Cheng M, Kung R, Hannah M, Wilansky D, Shime J (September 1995). "Menses cup evaluation study". Fertility and Sterility 64 (3): 661–3. PMID 7641929.
- "Green Eco Services". Green Eco Services. Retrieved 05/14/13.
- "pH Balance and You: Can't We All Just Get Along?". Instead Softcup Blog. Retrieved 05/14/13.
- Taylor, Bethany, M.D. "Using Tampons: Facts and Myths". SteadyHealth.com. Retrieved 05/14/13.
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- Livejournal Forum Forum with information including: brand and size comparisons; folding and insertion techniques; troubleshooting help for beginners