Many things about marriage and divorce rates have changed over the years. The average age of men and women when they get married has ticked upward. Divorce rates have gone up and down. But one thing has stayed relatively constant: what’s known as the “seven-year itch.”

It was made famous by the Marilyn Monroe movie over half a century ago. The reasons may be different, but the statistics are still the same. Seven years is the median age in a marriage when couples tend to separate.

People have always wondered why. Experts point to the stress of raising children, plus spouses’ slow realization that they are unhappy in their marriages. Work pressure and money issues can be factors, too.

According to an article on the Boston Globe’s website, people’s flaws or negativity can come out more as a marriage progresses, even if their positive qualities stay the same. Some people say it is impossible to know how a marriage will go until children enter the picture.

In addition, issues that aren’t necessarily related to the marriage directly can crop up and overwhelm people. Ill parents, expensive mortgages, daycare – it can all stress a person out, and when that fills up a life, sometimes there’s not enough room left for romance.

As for the Monroe movie, it was based on a George Axelrod play from 1952. According to the Globe, he was originally going to call it “The 10-Year Itch,” but seven had a better ring to it.

If he had only known.

Source: Boston Globe, “As pressures mount, unhappy couples still call it quits at 7 years,” Beth Teitell, July 29, 2011