A: Dear acocpa1:
I would take your daughter to a doctor. You are describing a longstanding problem with fears of dirt or disease that cause disruptive and compulsive activity, interfering with her peace of mind and the health of her skin. It is important that you and your daughter meet with a mental health professional who has the training and experience to make the proper diagnosis and to work with you and your daughter to form a treatment plan. A special therapy and perhaps medication might be prescribed, depending upon the results of a comprehensive evaluation. An ideal person to consult would be a child psychiatrist--a physician (i.e. medical doctor) who has had extensive training in the emotional problems of children and adolescents as well as adults.
I would start with your family doctor or pediatrician and ask for a referral for a comprehensive psychiatric evaluation. I would not wait, since your daughter has had this problem for several years already--and the sooner one starts effective treatment, the better the outcome.
In the meantime, you can offer your daughter your emotional support. You don't need to agree with her that her hair really needs to be washed because she has touched her hair after touching someone's backback--but you can agree that she somehow feels compelled to wash it and that she can't help feeling that way right now.
Good luck to you both.
Elizabeth Berger MD
Child Psychiatrist and author of "Raising Kids with Character"