Nits are actually the empty shells that are a white/cream colour in the hair and though unsightly they are completely harmless.
The reason for an infestation is down to head lice, they do not fly or jump they crawl from host to host. It is not just by head to head contact, it is from hair to hair contact. This is why people with longer hair are more prone to getting head lice.
Male head lice stay on the scalp feeding and mating, the female head louse is a lot busier, they feed and mate on the scalp, they lay eggs on the hair shaft close to the scalp so that the eggs can incubate in a warm place/. This is why nits are more prolific behind the ears and the nape of the neck because these are the warmest place on the head.
The female louse once has mated it
is capable of laying up to one hundred eggs in its twenty day lifetime. They are genetically programmed to colonize other hosts. So, after laying an egg it will journey down the hair shaft and wait to move to another head when it comes into contact with another persons hair.
If longer hair is tied in the nape of the neck this will help as hair will not be as likely to come into contact with someones hair. If you can imagine two children sitting at a desk sharing a text book and leaning forward, if the hair is not tied back or in a high up pony tail the hair will move forward and come into contact. Making it easy for the head louse to move over and start laying its eggs in the other persons hair.
The best way to prevent infestations getting hard to handle is to once a week use a nit comb and check the hair for these tiny little insect