What is head lice?

Head lice infestation is also called “Pediculosis capitis”. “Pediculosis” refers to louse infestation and “capitis” means the head.

Lice (Pediculus humanus variety capitis) are small insects that live on the skin over the head or scalp. Lice may also infect the body (Body lice – corporis) or groin (Public lice – Phthirus pubis). These are different from Pediculosis capitis. (1-6)

Ectoparasites

Head lice are called “ectoparasites”. They live on human skin and can survive only on human blood. They do not affect other animals.

Each louse takes several meals of blood each day and die if they are removed from the head for more than 2 days.

The lice are wingless and cannot jump but are good climbers that climb from hair to hair especially when it is dry.

When the hair is wet, the lice are unable to move. This makes it easier to remove those using gloved hands or a specially designed fine-tooth comb.

Laying of eggs

The adult female lice lay around 7 to 10 eggs a day and attach them to the hair using a glue-like, water-insoluble substance.

The site of attachment is usually close (1 mm) to the scalp.

The heat and the moisture of the human head help to incubate the eggs.

The common site for these eggs or nits is the back of the head or back of the ears.

Within 7 to 10 days the nymph emerges from the eggs and feeds on blood from the scalp.

Another 7 to 10 days and three moulting stages makes the nymphs adult lice.

How long do adult lice live for?

Each adult lives for around 30 days. Eggs survive for more than 2 weeks.

At any given time a person with an infestation has no more than 10 to 12 live lice but over a 100 eggs or nits. (2, 3)

How is head lice spread?

Infestation with this parasitic bug can spread by close contact with other people.

Head lice spread easily, particularly among closely grouped populations like school children.

Clothing and other articles like helmets, combs, hats, bedding may also help in spread of the infection.

How many people are affected by head lice?

According to the Centers for Disease Control and Prevention (CDC) 6 to 12 million people in the United States are affected each year with head lice.

Children between ages 3 and 10 years are most at risk. Girls are at further heightened risk since they have more frequent head-to-head contact.

Head lice affect people from all socioeconomic classes. African Americans are less at risk of infestations mainly because of differences in hair thickness and curliness. (1-4)

Symptoms of head lice

The eggs of the lice look like flakes of dandruff but unlike dandruff that flakes off the skin these stay hooked.

Eggs survive for more than 2 weeks.

Head lice leads to intense itching and rarely serious diseases are carried or spread by head lice unlike body or pubic lice infestations.

With severe infestation the lice may also be found in eyebrows and eyelashes.

Treatment for head lice

Head lice can be treated using medicated lotions or by wet combing, using a specially designed fine toothed head lice comb. (3, 5, 6)

Further Reading

• All Head Lice Content
• Head lice Causes
• Head lice Symptoms
• Head lice Diagnosis
• Head lice Treatment

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.