The answer is detergents. Milady's shop-safety guidance is explicit: "Never mix detergents with the bleach; always use bleach in a well-ventilated area." In practice, this means implements and surfaces need to be fully rinsed of any cleaning detergent before a bleach-based disinfectant is applied — mixing the two isn't just ineffective, it's a real chemical-safety hazard.
This is a genuinely common real-world mistake, not just a trivia point: a barber rinsing a fresh detergent wash straight into a bleach soak without an intermediate clear-water rinse is exactly the scenario this rule exists to prevent.
Milady Standard Barbering, 6th ed., Ch. 4 (Infection Control), p. 76: "Never mix detergents with the bleach; always use bleach in a well-ventilated area."
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