I just wanted to point out (in case no one noticed) that in the dermatological study results DeeAnna posted above, the soap with the highest pH - Johnson's Baby Oat soap with a pH of 12.4- rated the lowest on the irritability index scale.
That just goes to show how tenuous it is to rely on pH as an indicator of soap safety. Dr. Kevin Dunn said pretty much the same thing in his book, 'Scientific Soapmaking' on page 371.
By the way- Dr. Dunn also devotes a few pages of his book in Chapter 4 to the Tongue Test (zap test). He considers it a valid test and gives instructions on how to do it properly.
IrishLass
I did notice that and it made me do a double take!