Speaking at the White House's East Room during a pay equity event on Tuesday, President Obama unwittingly touched on the third rail of household errands in America when he talked about , wait for it, dry cleaning.

"We’ll talk about dry cleaners next, right," Obama said, prompting laughter from the audience, which was full of women, "because I know that -- I don’t know why it costs more for Michelle’s blouse than my shirt." Asked about the disparities between what men and women pay for dry cleaning during the daily briefing a little more than an hour later, White House press secretary Jay Carney replied: "It's terrible."

There's a surprising amount of data about the dry cleaning disparity. A few key facts:

1. Women routinely pay more than men to get their clothes cleaned professionally. In 2009 New York City resident Janet Floyd decided to survey dry cleaners there and found that when it came to laundering, men paid an average of $2.86 per shirt compared to the $4.95 women paid. Dry cleaners often complain their machines are built to launder men's garments, making women's clothing more labor intensive, and in some cases, they will only dry clean - -rather than launder -- women's shirts.

2. There is no overarching federal law that prohibits charging men and women differently for similar services. Charging women more for dry cleaning or a haircut, in other words, is different from discriminating on the basis of gender when it comes to housing or job decisions. There are some city and local ordinances that bar gender-based pricing, but even these have exceptions. The New York City Council adopted a bill banning “the public display of discriminatory pricing based on gender” in 1988, for example, but this does not apply to services that require a different level of labor.

3. If Obama took up the cause, he wouldn't be the first Democrat to do so. Mark Green, who served as public advocate in New York City and ran for any number of statewide offices, took on the city's dry cleaners for their pricing discrepancies.

4. The fight against gender-based dry cleaning pricing is not new.  In 1989, a group of George Washington University Law School formed the "Coalition Against Discriminatory Dry Cleaning" and filed complaints with the D.C. Office of Human Rights about unequal pricing at dozens of District dry cleaners. The city soon initiated a formal investigation of all dry cleaners. Two dry cleaning associations and the city brokered a settlement that called for equal prices. The law students also took on ladies' nights at bars, according to Professor John F. Banzhaf, who taught the students. Banzhaf said cleaners argued their equipment could launder a shirt for men between the size of "Pee Wee Herman and Arnold Schwarzenegger," but not women. (Banzhaf doesn't know if the agreement is still being honored.) Other suits were brought nationwide at the time. In San Francisco, a chain of 17 dry cleaners agreed to clean women's shirts for free for a month.