Evidence for Calcium Soaps in Human Hair Shaft Revealed by Sub-Micrometer X-Ray Fluorescence

The study used X-ray micro-fluorescence imaging to investigate calcium distribution in human scalp hair shafts, revealing two types of calcium. The first type, identified as calcium soaps, was easily removable by hydrochloric acid and found in the cortex, cuticle zone, and medulla core. The second type, likely involved in Ca 2+-binding proteins, was not easily removable and located in the medulla wall, possibly the cuticle, and uniformly in the cortex, with a consistent concentration across different individuals.