Hair Expertise

For some reason I saw some GMTV this morning. I usually shy away from such things because they are bad for my blood pressure. But I happened to be in the room and the TV was on and they were interviewing a hairdresser. And the hairdresser said:

"Of course, your hair changes every seven years....."

And the person talking to her just nodded and agreed. And my blood pressure went up (told you it would).

I just hate it when people make statements like these (and I hate it when others agree). What is the basis of saying this? How do they know? Why is it seven? Was my hair exactly the same for the first seven years of my life, and then turned another colour, or curly or vanished, until I was fourteen when it came back, or whatever? What happens if you are bald? Does this only happen on multiples of seven years. If you make it to 22 with a full set of follicles does this mean you are OK for the next six years?

I've done some research on this (actually searched for "hair changes seven years" on the interweb) and I did find one other person that mentioned this "fact". So I guess it must be true..