The acidity or alkalinity of a substance is measured on the pH scale, which ranges from 0 to 14. A pH of 7 is neutral, while values below 7 indicate acidity and values above 7 indicate alkalinity. Most teas, including black tea, green tea, and oolong tea, have a pH between 5 and 6, making them slightly acidic. This acidity is mainly due to the presence of compounds such as tannins and flavonoids, which are naturally occurring polyphenols found in tea leaves. Other factors that can affect the pH of tea include the type of tea, the brewing method, and the additives used such as milk or sugar. So, tea generally falls on the acidic side of the pH scale.