Even though baking soda is only a 9 on the ph scale that is and extreme difference from the 4-5 that hair naturally is. Any basic/alkaline product can cause raising of the cuticle and swelling of the hair strand = damage. Please do not take baking soda lightly there are relaxers that are as strong or only slightly stronger than it. Proceed with caution if you are using large amounts of baking soda or leaving it in your hair for long periods of time.
"Alkaline products cause the hair to swell, the cuticle to lift and remove oils from the air. This results in frizzy, dull, brittle hair that is prone to breakage and tangling. Extremely alkaline solutions cause the disulfide bonds between keratin protein molecules to break down and can eventually dissolve the protein completely. These types of solutions are the ones used to perm or relax the hair and can be extremely damaging, especially to hair that is already fragile."