CAUSES for Dry Hair
Sun, wind, and dry air pull moisture from hair the same way they do skin. Chlorine, salt water, and cold winter air pull it out too, just more gradually in the cold and more suddenly with a swim.
Shampooing too often strips away natural oils, especially with sulfates, which lift hair's outer layer and make it harder to hold onto moisture. Silicones make the problem worse from another angle, coating the hair shaft so moisture can't get back in once it's gone, and building up over time until it takes an even harsher wash to remove.
Heat styling and chemical processing break down the protein bonds that hold moisture in place, which is why blow-drying, coloring, and bleaching all leave hair drier afterwards. Hair that's already been bleached is even more vulnerable to heat, since its structure is already weakened.
Rough handling wears hair down the same way: brushing it wet, rubbing it dry, tight hairstyles, and rough pillowcases all add up over time.
Curly and textured hair tends to run drier by nature, since its texture and porosity make it harder for natural oil to travel down the hair shaft.