"I love your hair when it's combed back," a woman says to her grown daughter. "It looks so beautiful that way."

That's a compliment, right? It would be if her daughter's hair was combed back.

But her daughter's hair falls forward, so the comment implies, "Your hair looks unattractive the way it is." When her daughter snaps, "Well I'm wearing it this way today!" her mother asks, "What's wrong with you? Why are you so sensitive?"

If a daughter has children of her own, it can be deja vu all over again. "She would look so much prettier if she just brushed her hair," a woman says of her granddaughter — and her daughter is beamed back to childhood, when her mother was always at her to brush her hair. "She's fine the way she is," the daughter responds testily. "Leave her alone." The grandmother wonders how a harmless remark got her in trouble.

"I never know what's going to set my daughter off," one mother lamented to me. "Talking to her is like walking through a minefield."

Daughters and mothers agree on what the hurtful conversations are. They disagree on who introduced the note of contention because they have different views of what the words imply. Where the daughter sees criticism, the mother sees caring. She was making a suggestion, trying to help, offering insight or advice. Isn't that a mother's job?

Both are right, because caring and criticizing are bought with the same verbal currency. Any offer of help or advice — however well-intended, however much needed — implies you're doing something wrong.

Women have told me of their mothers — or their daughters — criticizing almost every aspect of their lives: clothes, weight, home decoration, how they raise their kids — plus trivial things, such as how much salt they put in the soup. But the topic I have heard about more than any other is hair.

What is it about mothers and hair? Pondering this while riding a bus, I scanned the women around me. Every one of them, I thought, would look better if her hair were different: longer or shorter, curlier or straighter, a more naturallooking color, a more stylish cut. I looked at the men. Every one of them had a nondescript hairstyle.

I then realized: There isn't any hairstyle for women that's nondescript. Every choice sends a message. Long, flowing hair that covers one eye: A woman who wants to look sexy. Short, sculpted hair: She's all business. Pulled back in a bun: uptight, repressed.

As every hairstyle incurs a value judgment, no wonder mothers fret over their daughters' hair. With so many styles to choose from, the chances are slim of picking one that others (including your mother) judge to be perfect.

Some of the resentment women feel about their mothers' attention to their hair (or clothes or weight) reflects their frustration that women in our society are judged by appearance because mothers typically enforce society's expectations at home. One woman tells me she said to her mother: "I'm sorry, but my lifetime interest in the topic of my hair has been exhausted."

One woman was annoyed when her mother commented that her hairdo needed improvement — and ran to get a brush and conditioning mousse to fix it. Later in the visit, the daughter criticized her mother's hair. She too applied mousse, then wound her mother's thin, gray hair around cans. She felt guilty because her mother's hair became stiff with dried mousse. But the next time they talked, her mother said how pleased she was that they had done each other's hair. She'd even told her best friend about it.

For the mother, how her hair looked wasn't the point. Attention to hair reveals — and creates — intimacy. When a daughter is grown, her mother may long to recapture the intense physical closeness she had with her child, although her daughter may resist it.

On the other hand, the daughter may relish it.

"I'm 65," a woman told me, "and my mother still brushes my hair out of my eyes." This can be maddening, but it can also be comforting because it's an intimate — and motherly — gesture.

One woman, while visiting her mother in the hospital, leaned over the bedrail, full of worry. Her mother's first words were, "When was the last time you did your roots?" The daughter immediately felt not anger but relief. Through the tubes and the fever, her mother was still there — still noticing, still caring.

Deborah Tannen is a professor of linguistics at Georgetown University and author of "You're Wearing THAT? Understanding Mothers and Daughters in Conversation."