Think of your hair as a pinecone. When the shampoo’s pH is below 7, the "scales" of the pinecone close, leaving hair smooth, shiny, and manageable. However, when the pH exceeds 7 (common in solid soaps, which typically have a pH of 8.0/8.5), the scales open, making hair appear dull and prone to tangling, creating that "bird’s nest" effect.