How the body reacts to certain foods is what determines what foods are alkaline-forming and what foods are acid-forming. For example lemons are acidic in nature, but have an alkalizing effect on the body once they are digested. Similarly, milk is alkaline outside the body, but acidic upon digestion.
Baking soda, or Sodium Bicarbonate, is a substance that neutralizes acids. In the body, it acts similarly. So, when I brush my teeth with baking soda and swallow it as I walk around the house it is an okay thing. I do not recommend dosing yourself with it. Instead I suggest watching the foods you eat.
The pH scale goes from 0 to 14, with 7 being neutral. Below 7 is acid and above 7 is alkaline. The blood, lymph and cerebral spinal fluid in the human body are designed to be slightly alkaline at a pH of 7.4.
A healthy pH level tends to also alleviate allergies as well as to discourage tumors.
To test your blood pH level, use test strips: