Health protection – guidance

Head lice (pediculosis)

The characteristics, transmission and management of head lice (pediculosis).

Head lice are parasitic insects called Pediculus humanus capitis. They only live on the heads of people.

Life cycle

There are 3 forms of head lice: nits, nymphs, and adults.


Nits are head lice eggs. The oval, yellowy white eggs are hard to see and may be confused with dandruff. They attach themselves to the hair shaft, and take about a week to hatch. The eggs remain after hatching, and many nits are empty egg cases.


Nymphs hatch from the nits. The baby lice look like the adults, but are smaller. They take about 7 days to mature to adults, and feed on blood to survive.


Adults are about the size of a sesame seed, have 6 legs, and are tan to greyish-white. The legs have hook-like claws to hold onto the hair with. Adults can live up to 30 days and feed on blood.


Anyone can catch head lice, but preschool children, primary school children and their families are most at risk.

Head lice are spread most commonly by close person-to-person contact.


See Public Health Medicine Environmental Group’s ‘evidence-based guidelines based on the Stafford report 2012 update’ for guidance on head lice control.

Read Public Health England’s ‘guidance on infection control in schools and other childcare settings’.

Treatment and prevention

For information on how to spot, treat and prevent head lice, visit NHS Choices.