The first time I fit into size 0 pants, I was so pleased that they fit that I bought them. I continued to feel the rush of being a size 0* for a few more months, until I was browsing among the Banana Republic sale racks when a woman confided in me, "I'm not a real size 0. I don't know where the actually skinny people shop these days."
Then I realized that I had been duped by vanity sizing, a gimmick companies use to get women to buy clothing by making them feel good. I had always heard that though Marilyn Monroe wore a size 16, she was not actually fat, but I had not realized to what extent clothing sizes have been shifting. The growth seems to have been particular aggressive in the last couple of years: as the Boston Globe says, 0 is the new 8. When I was 12, I was a size 3/4; at 22, I have become a size 00 in and can no longer find appropriate-length pants in American stores. Though I seem to decrease in American size each year, I remain a size 4 on the European scale..
Vanity sizing is harmful because 1) it encourages obesity while 2) perpetuating unhealthy pressures to look a certain way and 3) makes it very difficult for small people to buy clothing. When women try to lose weight, they often have clothing sizes as targets. This becomes meaningless as the sizes become moving targets in favor of those who have gained weight. Also, a woman remains the same size over the course of a few years may have actually gained a significant amount of weight. Especially since Americans have grown larger and obesity has become such a public health issue that New York governor Paterson has proposed an "obesity tax", it is not a good change that clothing sizes no longer serve as an indicator of whether someone may need to watch his or her weight. One argument people have made in favor of vanity sizing is that because size 0 is now associated with average-looking people, it takes away the pressure for women to be anorexic waifs. But wait a minute, isn't shifting the whole sizing chart just a way of legitimizing pressures to be a smaller size (and helping people cheat at it)? As long as there exist people who are rail-thin (naturally or otherwise), there will be clothing manufacturers who make clothes for them, and there will be girls who yearn to be that thin. Inflating sizes does not get rid of the size-0 fetish, it just decouples the size-0 fetish from the actual size 0. Inflating sizes also makes it more difficult for the previous size 0's (and previous size 2's, 4's, and 8's) to buy clothing. As clothing has become larger, the list of stores where I can shop has been shrinking and I can never get anything on sale. For instance, I cannot shop at J. Crew for pants at all anymore! I have spent increasingly more money and time just to buy clothes that fit.
Many people say that vanity sizing is not as bad as the lack of a standard. Differing rates of vanity sizing makes buying clothing inefficient, as I now have to try on a range of sizes even at stores where I knew my size 3 months ago. It is also impossible to predict how things will fit when shopping online. (Sometimes the inflation is so bad that I know to just go down a size from the previous time. Absurdly enough, by the time I run out of sizes the store may have added an even smaller size--e.g., 00, XXXS.)
Though I do not know how much longer stores can go enriching their Petite lines and adding smaller sizes, it seems unlikely that a brand will stop or reverse this process. One way to stop this is to have regulations for standardizing clothing sizes. A way to implement regulation is to create a standard based on measurements and tax companies that do not adhere to standards by an amount comparable to how much they make from vanity sizing. (To address the argumen that a medium-sized barrel-racer need not fit into a medium-sized tutu, the regulation could either exempt niche clothing or have different standards.) Other countries have begun regulating sizes, though for the purpose of reversing pressures for women to be too thin. Vanity sizing is bad enough for American women in the other direction that regulation would not be inappropriate. (Does anyone know of studies on how vanity sizing has affected the sizes of American women?)
* Size 0 used to be associated with the anorexic-waif look, which was unattainable by most but desired by many. Since recent size inflation, this association has become meaningless.