Understanding Head Lice

AUGUST 04, 2014
Guido R. Zanni, PhD

Although very contagious, head lice can be treated and prevented.
Head lice are insects with 6 claws and no wings. Lice cannot hop or fly. Lice move by crawling. Their claws hold tightly onto hair. They are gray-white or tan and the size of sesame seeds. Lice feed on human blood 4 or 5 times a day. Lice live and breed within a quarter inch of the hair from the base of the scalp, especially near the ears and neck. Head lice may also thrive in eyebrows and beards. Lice are most active at night.1,2

Head lice are very contagious. Lice are spread by direct contact with someone who is infested or by sharing clothing (eg, hats) with someone who has lice. Female lice attach their eggs firmly to hair. Lice eggs are called nits, which are usually yellow to white. Nits are extremely small and can be confused with dandruff. Nits hatch in 8 or 9 days. They reach adult size in 9 to 12 days after hatching.2 Lice live up to 30 days. Females can lay 50 to 150 eggs in their lifetime.1,3 If lice fall off the scalp, they die within 2 days.

Six to 12 million children, mostly between 3 and 12 years of age, get lice each year.1,4 It is more common in girls and in individuals living in crowded conditions. 5 Head lice is less common in African Americans.2

How Can I Tell if My Child Has Head Lice?
The first symptom of head lice is intense itching. Other symptoms include a tickling sensation or a feeling that something is moving in the hair. Small red bumps on the scalp or neck may also be present (Table 12).6 Constant scratching can result in open wounds and infections.5

Myths and Facts
Myth: Pets spread head lice.
Fact: Lice cannot live on pet fur.

Myth: Head lice carry diseases.
Fact: Lice do not carry other diseases.

Myth: Head lice thrive in dirty households.
Fact: The cleanliness of a person or house has no role in spreading head lice.

Myth: Insect sprays kill lice.
Fact: Insect sprays should never be used. They may contain harmful chemicals.

Myth: Swimming spreads lice.
Fact: Lice tightly hold onto hair when underwater. Chlorine in pool water cannot kill lice.2

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