Although there are many types of lice, the head louse, or Pediculus humanus capitis, is a parasitic insect that can be found on the head and, more rarely, the eyebrows and eyelashes of people. Head lice (the plural form of louse) feed on human blood several times a day and live close to the scalp to maintain their body temperature.
Head lice come in three stages: egg, nymph and adult (learn how big lice are in their various stages). Eggs are often called lice nits, although many people refer to nits as the empty egg shells left behind by a hatched louse.
A head louse has six claws that allow it to crawl around from hair strand to hair strand. It can move from one head to another this way, which is why head-to-head contact is the primary way head lice are spread between people.
A head-lice infestation occurs when a female adult louse makes it onto a new head and lays eggs. When those eggs hatch, the lice will most likely stay on that head throughout the entire lice life cycle. Unless the head is treated (see pediculosis treatment) and all lice and eggs are killed, the lice infestation will continue for however long the lice can live.
Adult lice will be the easiest to spot because they are the biggest. But at the size of a sesame seed, they still aren’t that big. Although lice vary in color, if you see a grayish-white or tan bug crawling through the hair, it is probably a louse. If you look closely at an adult louse, you should be able to see human blood inside it.
Look at the hair strands about a quarter inch (~0.5 cm) off the scalp. See if you can find lice eggs (often called nits) attached to individual hairs. Nits are extremely small. They look like tiny specks and will be glued pretty securely to the hair. If you see any, try pulling them off with your fingers. If you can’t easily pull them off, they are probably eggs and not dandruff.
The primary way you can get head lice is when your head comes in direct contact with the head of an infested individual. Head-to-head contact like that doesn’t guarantee that the infestation will spread, but it gives lice the best opportunity to move from the hair of the infested person to your hair.
Head lice don’t jump, swim or fly. Without strands of hair to grab with the claws on their legs, they have trouble getting around at all. However, they can crawl pretty quickly along the hair, so if your hair comes in contact with an infested head, it doesn’t take much for a louse to hitch a ride on a strand of your hair and make its way to your scalp.
Excluding the 8-9 days they spend as eggs, head lice can live for around 30 days on your head. As parasites, they feed on human blood several times a day.
If they are removed from their food source – say from getting knocked out of your hair with a brush or your hand – they can survive 24-48 hours. If they don’t find some human hair to crawl back to a new host during that time, they will die.
There are many ways you can kill lice. You can suffocate them, poison them, or dry them out. You can also starve them if you get them away from their food source – your head – long enough (they’ll die within 24-48 hours).
Head lice do not survive long if they fall off a person and cannot feed. You don’t need to spend a lot of time or money on housecleaning activities. Follow these steps to help avoid re–infestation by lice that have recently fallen off the hair or crawled onto clothing or furniture.