The louse (plural: lice) is a parasite that attaches itself to human hair and feeds on human blood. The most prevalent kind of lice is head lice. An infestation with head lice is medically known as Pediculosis capitis. The Centers for Disease Control and Prevention (CDC) estimate that up to 12 million lice infestationsTrusted Source occur every year in the United States.

Female adult lice can lay up to six eggs every day. Eggs are laid right onto the shaft of hair. Those that are less than six millimeters from the scalp are most likely to hatch. The eggs are essentially glued on to the hair by secretions from the female louse.

The eggs take about a week to hatch, producing a nymph. The nymphs then go through three successive growth spurts. During these spurts, they molt until they reach adult size.

Adult lice are about the size of a sesame seed and can be very hard to see, because they can be any color from white to tan to brown.

Lice typically feed on blood four to five times each day. They use their mouth parts to bite into the skin and secrete a substance that acts to block clotting.

While it’s important to note that lice infestations can happen to anyone, some people are at a higher risk of coming into contact with lice.


Head lice

Head lice are obligate parasites. This means that they cannot survive without a human host. This species can live only on human hosts, so you cannot get them from your dog, cat, guinea pig, or any other kind of furry pet you may have.

Lice don’t have wings, so they can’t fly. They have six legs with claws at the ends — that’s how they attach themselves to hair.

Head lice can settle anywhere on the scalp, but they’re commonly found on hairs at the back of the neck and around the ears, where it’s warmest.