pH is a measure of the acidity of a substance. More specifically, it measures the proton concentration via the following equation: pH=-log[H+]. The pH level will absolutely affect the effectiveness of soaps, detergents, and stain removers. Many stain removers and detergents contain enzymes to help break down stains. Enzymes are proteins and consist of long chains of amino acids. Proteins are designed to operate most efficiently at a particular pH. If the pH of their environment is changed too much, the protein will denature and lose its shape, thereby losing it's ability to function (in this case breaking down stains and soils). Soap itself is made under highly basic conditions, meaning a very high pH. As such the polar part of soap is in salt form. Using soap under highly acidic conditions can affect this salt and therefore the effectiveness of the soap's cleaning abilities.