What are nits and lice?

Head lice (scientific name Pediculus capitis) are parasitic insects that feed on human blood, cause itching from their bites but they do not carry disease. Lice can cause bacterial infections only when a bite is scratched with a dirty finger.

The plural of louse is lice, a nit is the egg and a nymph is a young louse.

Head Lice is the second most common communicable disease affecting schoolchildren, after the common cold.

The adult louse resembles a dark sesame seed or small black grain of rice and can be light brown to grey to black in colour with six legs and is slightly transparent as an adolescent. The older the louse, the darker their colour. Head lice are sensitive to temperature and humidity and the head is a perfect environment for these parasites. The lice control their temperature by moving to different parts of the scalp – warmer under the pony tail, cooler around the hair line.

Lice move quickly over the scalp using their specially designed legs. Each of their legs grasp the hair shaft with a tiny claw at the end. This enables the louse to move rapidly around the scalp making them difficult to spot on dry hair. The claws however mean that head lice cannot fly or jump. Their grasp is very strong which makes them hard to dislodge from the scalp and hair. Head lice do not burrow into the skin.

Nits are small, brownish/grayish and oval shaped eggs and are ‘super glued’ at an angle to the side of the hair shaft. The louse lays nits very close to the scalp where the temperature is perfect. Eggs further than 1-2cm from the scalp are usually empty cases which remain attached to the hair after the nymph has hatched (often white in colour). If you can blow or flick it off, or if it crumbles in your fingers, it is not a nit.

People often mistake dandruff or ‘hair casts’ (HCs) for nits. HCs are thin, elongated, firm, whitish cylindrical in shape, which encase the hair shaft and can be easily dislodged (often by sliding without force down the hair shaft). There are two different types of HCs – peripilar and parakeratotic keratin cast. Due to its similarity to head lice, its also known as ‘pseudo-nits’.