Most families reach for a bottle of lice shampoo first — and it makes complete sense. When lice are discovered, the instinct is to grab something from the drugstore and deal with it quickly. But for many Denver families, that approach leads to weeks of frustration and reinfestation, not because they didn’t follow the instructions, but because the product simply didn’t do what they hoped.

Chemical resistance is a well-documented and growing problem. Common over-the-counter shampoos rely on permethrin or pyrethrin-based insecticides, and lice populations have increasingly developed resistance to them. Studies have found that the majority of lice in the U.S. carry mutations that make these treatments far less effective than they once were. But even when a chemical treatment does kill live lice, it typically does little or nothing to the eggs. Nits are cemented to the hair shaft and can survive chemical exposure, meaning even a seemingly successful treatment can leave dozens of viable eggs behind, ready to hatch within a week. The cycle most families know too well: treat with OTC shampoo, feel relief, watch lice return a week later, and repeat. The eggs were never removed.