“As their hair line is eroding, so is their self-confidence and attractiveness,” said Mr. Kobren. “We call it a cancer of the spirit.”…

Because of the blow to their self-esteem, some balding men simply settle when it comes to spouses, Mr. Kobren said. “Guys believe they don’t have much time left as they continue to lose their hair. They kind of grab the person closest to them who they find relatively attractive at the time. Emotionally it’s too difficult for them to go out there and try to court the girl of their dreams if they are feeling emotionally insecure about themselves.”

Although Ms. Middleton and most other women aren’t likely to admit having an aversion to balding men, Susan Jones, an executive at an accounting firm in Manhattan, said many of her female friends in their late 30s and 40s are alone, in part, because their “impossibly high” criteria for men have little to do with what it takes to be a good husband. “They want to date these good-looking men, but really, that’s not going to get you very far in a marriage,” said Ms. Jones, who pointed out that she has been happily married to Richard Jones, who is bald, for 13 years.