Ms Liang was telling us about the Dove commercial. It's something to do with ph scale. Acidic and alkali are two extremes that describe a chemical property chemicals. Mixing acids and bases can cancel out or neutralize their extreme effects. A substance that is neither acidic nor alkali is neutral.

The ph scale measures how acidic or basic a substance is. The pH scale ranges from 0 to 14. A pH of 7 is neutral. A pH less than 7 is acidic. A pH greater than 7 is alkali.

The amount of hydrogen ions creates the acidicity of the substance. take a look at this diagram:


So the commercial's aim is trying to say that the ph level is 7, which is the same as water and i suppose it's good for the skin.