Headlice Eggs (Nits) are and evolutionary masterpiece... waterproof, extremely tough and resilient.
The Nit Eggs have multiple Spiracles on the cap of the egg shell allowing a growing louse the ability to breathe whilst in the egg. Like a chicken egg the louse begins its life as a fertilised liquid.. in fact once mating act results in all 30 or so eggs within the breeding female louse being fertilised all at once. She then lives for about another thirty days laying her little bundles at around 3-4 a day.
Why repeat headlice treatments after seven days?
The louse within the nit egg, once old enough, can open and close the breathing spiracles as required and therefore they can survive being submerged in water, hair products such as shampoos and conditioners and even head lice treatments.
This is why it is so important to repeat headlice treatments again after seven days in warmer weather and fourteen days in cooler climates, giving the little louse time to hatch, so you can catch the little sucker before it gets a chance to grow into a fully breeding adult louse.