You may have heard that mayonnaise kills head lice. And that's true, although there are less messy and more effective ways to treat lice.
Products like mayonnaise kill lice through suffocation. If you were to look at a louse under a microscope, you'd find a series of openings along the side of the thorax that allows air into the respiratory system. These holes are called spiracles. And just like you'll die if your air supply gets cut off, lice will die if their spiracles get plugged up.
So the intent of suffocation products is to kill lice by filling in, coating or paralyzing their spiracles. Besides home remedies like mayonnaise, Vaseline or olive oil, there are commercial suffocation products specifically for treating lice. These products are often lotions or sprays that can contain silicone-based ingredients.
Unlike lice pesticides, suffocation products aren't necessarily regulated by the FDA.
The efficacy of suffocation products depends on the thoroughness of the application, and the time spent on each treatment. Since the spiracles can't be seen with the naked eye (they are hard to see even in lice pictures), it is hard to know whether they are getting plugged with the product. Treating lice with suffocation products usually requires many hours and multiple treatments.
As is the case with pesticide-based products and herbal remedies for lice, suffocation products have a tougher time affecting the lice eggs (also called nits). The low efficacy in killing lice eggs means the head-lice problem continues as soon as the nits hatch, requiring additional applications of the suffocation products. That is in contrast to heated-air treatments like the AirAllé® device which kills 99.2 percent of lice eggs.