Baking soda is alkaline and therefore raises the cuticle, making hair rougher, drier, and more porous. This is why a vinegar rinse is absolutely necessary, to lower the pH of the hair back to it's natural 5 and smooth down the cuticle. Because curls need moisture, bs can loosen curls.
My hair is porous, medium thickness, good elasticity, medium density, 2c/3a, APL, dark brown with a silver lining. Biggest enemy: frizz!