I stopped at the local Medicine Shoppe chain to fill my sons rx for his acne (duac and differin) and thought maybe they might stock ph test papers. I remember years ago being able to buy them and test my cosmetics with them.
Well, they had them, a huge tube for $7.

I have had more fun dipping them in my skin stuff and seeing what the actual ph is! For ex. the Aveeno Positively ageless cream I was concerned with because of it's glycolic acid content came out at a ph of 6 -- which renders the aha ineffective! No worrys here!
My Clinique liquid soap is a perfect ph neutral, as is the Aveeno Ultra-calming cleanser. Yay!
Who would think dipping and testing would be this much fun!
I highly rec buying these, it takes the guesswork out of gauging whether or not your alph/beta hydroxys are effective or if a product is too harsh or not.