In Vitro Evaluation of the Efficacy of 27 French Over-the-Counter Anti-lice Treatments

Head lice remain a major public health problem worldwide, with a high prevalence among schoolchildren. Many lice treatments are available, but their efficacy is often poorly evaluated. An increase in the resistance of parasites to neurotoxic therapies, combined with a partial efficacy of certain suffocating agents, can contribute to the maintenance or even rise in infestations. The study aims to evaluate the effectiveness of 27 different over-the-counter lice treatments available in France in 2024 for eliminating lice and nits. To do this, we used the subspecies Pediculus humanus humanus, a well-established model organism for competitive studies. The products were purchased in France from randomly selected pharmacies and then tested in the laboratory on lice and their eggs. The laboratory conditions of the in vitro tests were designed to reproduce the exposure times and application methods recommended by the manufacturers. A parallel study was carried out on sales data for anti-lice products from French pharmacies. The results allowed the classification of the 27 products into four groups: five products demonstrated potentially 100% pediculicidal and ovicidal activity; four products showed potentially 100% pediculicidal activity but insufficient ovicidal activity; another four products exhibited potentially 100% ovicidal activity but insufficient pediculicidal activity; and the remaining 14 products showed insufficient activity against both lice and nits. Sales data show that only 27% of products sold in French pharmacies are able to completely cure pediculosis. The French market for lice products is mainly occupied by treatments with a lack of effectiveness. Health authorities should require thorough efficacy assessments before registration and conduct periodic reviews to ensure the effectiveness of these treatments sold in pharmacies.