Because hair is dead fiber that cannot heal: the protective cuticle wears away under heat, bleach, and friction, then the shaft fractures lengthwise - lab simulations show damaged hair's splits propagate far along the strand, and bleaching healthy hair makes it split the same way.
Serums cannot weld a split - they glue it visually until the next wash. The real fixes: trims every 8 to 12 weeks, less heat, conditioner every wash, gentle handling of wet hair. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper .
What to do
Common questions
Why do I get split ends?
Because hair is dead fiber, not living tissue - it cannot heal, so everything it endures accumulates until the shaft fractures lengthwise. Biomechanics research that simulated combing forces in the lab shows how it happens: the protective cuticle scales wear off first, then microcracks form inside the strand under repeated bending and friction, and in damaged hair those splits propagate far along the fiber; in the same experiments, bleaching healthy hair made it split like naturally damage-prone hair. That maps onto the daily causes: heat styling, bleaching and dye, rough towel-drying, tight elastics, dry brushing, and plain length - the ends of long hair have simply survived more years of wear. What does not work: serums that "repair" split ends - a split shaft cannot be welded, only glued down visually until the next wash. What works: trim every 8 to 12 weeks, lower the heat and add protection when you use it, condition every wash (conditioners deposit smoothing layers that cut fiber friction), and go gentle on wet hair, which stretches and snaps at its weakest.