Mayonnaise is commonly used as a home remedy to kill head lice, but its effectiveness is not scientifically proven, according to WebMD. To smother lice, a thick layer of mayonnaise is applied to the infected person's head and left on overnight underneath a bathing cap.
While there is no proof that mayonnaise kills lice, pediatricians state that there is no harm in trying this simple home remedy, as noted by WebMD. It should not, however, be used as a main treatment.
Over-the-counter lice treatments, which typically contain chrysanthemum extract, are effective at killing lice and are generally safe, according to WebMD.