Wet Combing for Head Lice: Four Passes, Four Sessions — A Schedule Set by the Egg, Not the Adult

Wet combing with a fine-toothed comb is the main non-chemical treatment for head lice, and it is usually abandoned because it is done once. This study models removal with a 0.22 mm tooth gap and stated per-pass removal fractions (adults 0.72, nymphs 0.58, eggs 0.18) from a starting load of 18 adults, 30 nymphs and 120 eggs. One four-pass session removes 97.8 percent of mobile lice but leaves 54.3 eggs, which is why a single session fails. Combing on days 1, 5, 9 and 13 — spaced so that eggs hatching on days 6 to 9 meet a session before those nymphs can mature — ends with 0.00 adults, 0.01 nymphs and 2.8 eggs. The same effort compressed into days 1 and 13 alone leaves 0.79 nymphs and 13.5 eggs, a surviving bridge to a fresh generation. The originated schedule is four sessions of four passes over 13 days (about 25 minutes each), and the paper shows that the calendar, not the combing intensity within a session, is the variable that decides success: six passes in one session still leave 36.5 eggs. This study is simulated, not measured. SIMULATED, NOT MEASURED.