While I am not entirely certain about acne products, I do know that the pH of shampoo can be very important to its performance. Let me first mention a few things about hair. A hair consists of a central region, and an outer shell. The outer shell is called the cuticle, and reminds me of a pine cone. The outer cuticle can either lie flat and closed or it can "fluff" up and out. When the cuticle is fluffed out, light scatters off of the hair in a very diffuse manner, and the hair looks dull. When the cuticle is flat, the hair looks shiny and healthy. It turns out that when the hair is exposed to a silghtly acidic environment, the cuticle lies down and the hair looks the best. Additionally, hair is stronger when in an acidic environment. This may be due to the cuticle laying flat, but i am not certain.

I found the answer to this question in a book called The Extraordinary Chemistry of Ordinary Things. If your library does not have it, I would recommend it strongly to your librarian. In this book you can find more details about the question of pH balance.

I'd like to propose a little experiment for you to test one of my hypotheses about shampoo. We have seen that acidic shampoo makes the hair look good, but of course if it is too acidic, it will burn if it gets in the eyes. You are most likely aware of shampoos which are designed for children and may be marketed as "no-tears" brands. I think it would be an interesting project to test the pH of shampoos with litmus paper. I would imagine that the baby shampoos are far less acidic than adult shampoos. If you try this, I would be interested in hearing the answer.