The Adherent Cylindrical Nit Structure and Its Chemical Denaturation In Vitro: An Assessment With Therapeutic Implications for Head Lice

Head lice: Scientific assessment of the nit sheath with clinical ramifications and therapeutic options

“…Chemical denaturation does occur with the use of very strong acids to the solid state of the nit sheath; however, 5% acetic acid, 8% formic acid, and the enzymatic nit removers currently marketed do not have any visible effect on the nit sheath by examination under light microscopy. 9 Similar to various other species, the glue of the head lice is liquid within collateral glands but solidifies when exposed to air. 3,[10][11][12][13][14][15][16][17][18] In the case of body lice, Carter 3 found that the glue solidifies within seconds of exposure to atmospheric air.…”

“…9 Flash pyrolysis-gas chromatography/mass spectrometry shows that the nit sheath, or insect glue, is composed of protein, possibly cross-linked to aliphatic components. 10 The protein composition is similar to that of hair keratin, although it is structurally more rigid, possibly because of the large amount of tyrosine and phenylalanine residues, which could allow hardening of the nit sheath.…”

Head Lice

“…Hair pomades are easier to remove but may not kill eggs, and treatment should be repeated weekly for 4 weeks. 61 Other occlusive substances have been suggested (mayonnaise, tub margarine, herbal oils, olive oil), but to date, only anecdotal information is available concerning effectiveness. One study that examined several "home remedies" (vinegar, isopropyl alcohol, olive oil, mayonnaise, melted butter, and petroleum jelly) revealed that the use of petroleum jelly caused the greatest egg mortality, allowing only 6% to hatch.…”

“…9,61 This product has not been tested with and is not recommended for use with permethrin, because it may interfere with permethrin's residual activity. A variety of other products, from acetone and bleach to vodka and WD-40 (WD-40 Company, San Diego, CA), have proved to be ineffective in loosening nits from the hair shaft 61 and present an unacceptable risk to the patient. It seems that nature has protected the louse by making the nit sheath similar in composition to the hair, so that agents designed to unravel the nit sheath can also damage human hair.…”

Head Lice

“…7,68 This product has not been tested with and is not indicated for use with permethrin, because it may interfere with permethrin's residual activity. A variety of other products, from acetone and bleach to vodka and WD-40 (WD-40 Company, San Diego, CA), have proved to be ineffective in loosening nits from the hair shaft 68 and present an unacceptable risk to the patient. It seems that nature has protected the louse by making the nit sheath similar in composition to the hair, so that agents designed to unravel the nit sheath can also damage human hair.…”