Removing head louse eggshells and nits after a successful pediculicide treatment is often made more difficult because it is not easy to see them all amongst the hairs. Therefore, a treatment that makes louse eggs more visible potentially makes the task of removal easier and reduces the risk that children would be sent home from school or over-treated. This project involved the development of a hair treatment gel concept that was easy to apply, wash out, and that stained louse eggs and nits but without staining the hair and skin. A series of food-grade dyes were evaluated for their ability to stain the eggshells, and various copolymer-based rheology modifiers were tested for dye compatibility and stability. Several dyes were rejected because either they failed to stain louse eggshells or else stained skin too easily. Two dyes, Patent Blue and Ponceau 4R, were eventually selected for different product developments, one specifically for post-treatment nit removal and the other for pre-treatment diagnosis. In clinical field studies, both were found to make the treated eggshells contrast sufficiently with the hair to enable identification of persistent nits. Use of a nit stain product can enable easier detection of louse eggs and nits, thus facilitating the removal process and reducing the risk that persistent eggshells could be mistaken for signs of a continuing infestation.
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