Lice resistance is a popular topic because lice have now evolved a resistance against many preparations that are used. It’s well documented in scientific literature that these products produce clinical failure. Lice have developed this kind of resistance over time much like bacteria have developed resistance against penicillin and other antibiodics. They reproduce very quickly and therefore can develop resistance very quickly.   There are basically 2 products that would be very, very difficult for lice to develop resistance against. That would be simple mechanical treatment using lice combs which physically remove head lice and eggs from the head. Or there is a new medical device, AirAlle, that dehydrates and uses heated air. That is also very unlikely to allow for the develop of resistance.