Bleach has a pH value of around 12 or 13. The pH scale is used as a measure of the acidity or basicity of solutions in which the solvent is water. Solutions with a pH value of 7 or less are acidic, while those above this number are basic.
Pure water has a pH value of 7. Substances with lower, or more acidic values, include lemons (2.2), wine and beer (4.0) and battery acid (1.0). Substances with higher, or more basic, pH values include bleach, as well as ammonia (11.0) and human blood (7.4). Bleach can be considered extremely basic at pH 12, and should not be allowed to contact bare skin.