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. Menstrual cups are usually made from medical grade silicone.
Manufacturers have different recommendations for when to replace the cups, but in general they can be reused for years. Disposable menstrual cups are also available - these work in the same way as a regular menstrual cup except they are disposed of after every use or (for some brands) after every cycle.
An early version of a bell-shaped menstrual cup was patented in 1932, by the midwifery group of McGlasson and Perkins. 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.
Whilst several companies in Canada, UK, Germany and South Africa are in the meantime offering this product it is still surprisingly little known. One reason might be that it is difficult for the companies to make much profit from this product as one single menstrual cup can last a girl or woman five years or longer. Some non-governmental organisations (NGOs) and companies have begun to propose menstrual cups to females in developing countries since about 2010 (for example in Kenya and South Africa) as a possible low-cost and environmentally friendly alternative to rags, disposable pads (often very expensive in developing countries) or "nothing" - the reality for many females in developing countries.
The menstrual cups currently available can be divided into two basic types:
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.
Sizing and Selection
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. The larger size is normally recommended for women over 30 or who have given birth vaginally. 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 uncomfortable. Length also needs to be considered: if a woman's cervix sits particularly low, she may want to use 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.
A final consideration in selecting a menstrual cup is firmness/flexibility. Certain brands are firmer than others, the firmness of certain brands varies according to size. A firmer cup pops open more easily after insertion and may hold a more consistent seal against the vaginal wall (preventing leaks), but many women find softer cups more comfortable.
Most menstrual cups come in colorless, translucent silicone. Several brands offer colored cups in addition to (or instead of) the colorless ones. Colored cups use a dye that is certified to be safe for food. Translucent cups lose their initial appearance faster than colored - they tend to get yellowish stains with use. The shade of a colored cup may change over time, though stains are often not as obvious on colored cups. Stains on any color of cup can often be removed or at least lightened by soaking the cup in diluted hydrogen peroxide and/or leaving it out in the sun for a few hours.
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, the user 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. There are a number of different folding techniques that can be used for insertion. 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. Simply pulling on the stem is not recommended 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. Alternatively, sterilizing solutions (usually developed for baby bottles and breast pump equipment) may be used to soak the cup.
Menstrual cups are safe when used as directed and no health risks related to their use have been found. However, no medical research was conducted to ensure that menstrual cups were safe prior to introduction on the market.
One case report in the journal Gynecologic and Obstetric Investigation noted the development of endometriosis and adenomyosis in one menstrual cup user. Additionally, after one survey with a small sample size indicated a possible link, Associated Pharmacologists & Toxicologists and Endometriosis Research Centre issued a combined statement that urged further research. 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.
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."
- Since they are reusable, menstrual cups help to reduce waste. Some disposable sanitary napkins and plastic tampon applicators can take 25 years to break down in the ocean and can cause a significant environmental impact. However, biodegradable sanitary options are also available 
- Reusable menstrual products (including menstrual cups) are more economical than disposable ones; in the long run a woman will save money by using a menstrual cup.
- There are reasons to believe that using menstrual cups is healthier for the vaginal environment than using tampons. Tampons absorb all vaginal moisture, including secretions that are needed to maintain the proper pH and beneficial bacteria populations.  Menstrual cups collect menstrual flow and allow the vagina to regulate its own moisture levels. The bleaching process many tampons undergo can produce trace amounts of dioxin, a suspected carcinogen—although whether this causes health problems has not been firmly established. There are unbleached options available for women who have concerns about the bleaching process. In any case, menstrual cup use is not associated with Toxic Shock Syndrome, an infection that can often be traced to improper tampon use. Potential users of the menstrual cup are advised to check with a doctor before using the menstrual cup if they have previously experienced Toxic Shock Syndrome.
- 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.
- Menstrual cups collect menstrual fluid inside the vagina and may not leak (if emptied often enough). However, some women do experience leakage due to the location of their cervix 
- 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 report that they bleed less or have shorter periods or fewer cramps when using a menstrual cup as opposed to tampons.
- Individual menstrual cups are more expensive than a package of sanitary napkins or tampons and require some upfront investment. One woman calculated that within about six to twelve months a menstrual cup saved her money, but this depends on the type and cost of disposable products used previously and how frequently they were changed. A menstrual cup typically costs somewhere between US $25 and $40. Generic cups can sometimes be found for as little as $10, though these may be illegal copies of branded cups and may not be from reputable sources.
- Some women experience difficulty in inserting or removing the menstrual cup depending on previous experience and 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.
- Some women find menstrual cups uncomfortable. This may lessen with practice inserting the cup, selecting a smaller or softer cup, and/or trimming the stem of the cup, if present.
- 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 (or tampons) comfortably or safely.
- Many menstrual cup companies recommend that women using IUDs for contraception who are considering using menstrual cups should consult with their gynecologists before use. There have been rare cases in which women dislodged their IUDs when removing their menstrual cups; this can also happen with tampon use.
- Removing a menstrual cup can be messy, with spillage of menstrual blood.
- Cleaning menstrual cup in a public toilet can pose problems as the facilities to wash the cup are public. Some manufacturers suggest wiping out the cup instead of washing it, but this practice might increase the risk of infection. Certain users carry a small bottle of water in their purse to rinse the cup privately over the toilet. Since menstrual cups often only need to be emptied every 8-12 hours, many users do not have to empty in public restrooms frequently. 
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- Livejournal Forum Forum with information including: brand and size comparisons; folding and insertion techniques; troubleshooting help for beginners
- Menstrualcup.co Website with information about menstrual cups in general, step by step guide on to use a menstrual cup, comparing all brands, large FAQ and blog.