Head Lice Eggs

Head lice eggs occur in three states:

• Live egg
• Dead egg
• Hatched egg

Being able to identify the state of the egg is important. Hatched and dead eggs are historical evidence of infection, but are not an infection risk. If a child has hatched or dead eggs only, and no live eggs or no climbers, they do not have an active infection. No treatment is needed for inactive pediculosis.

How do I tell the state of the egg?

Check the following:

• The shape in profile:
  Hatched eggs have no operculum and look like a boiled egg with the top cut off.

  The overall shape:

  Dead eggs collapse in on themselves and the sides are crumpled.

  The colour:

  Live eggs are brown; hatched eggs are pale; dead eggs are brown.

  The pressure inside the egg:

  Live eggs "pop" when squashed between the nails; dead eggs and hatched eggs don't.

The following photographs of head lice eggs have been made using a scanning electron microscope (SEM). The SEM is great for showing details of eggs, but the pictures are in black and white only.

Live Egg

The complete egg consists of a tube which encircles the hair shaft with the egg attached to the end furtherest from the scalp. Note the operculum forming a lid on the top of the egg. To hatch the operculum opens. Live eggs have curved walls.

An unhatched egg has the operculum in place

Dead Egg

Dead eggs have the operculum in place, but the sides of the egg have collapsed inwards. Probably a live embryo is needed to maintain pressure in the egg, and when the embryo dies pressure falls and the atmospheric pressure forces the walls in.

Hatched Egg

Hatched eggs have lost the operculum, and have a flat top in profile.

Remember:

• live eggs = active infection and an infection risk
• dead eggs only = inactive infection; no infection risk
• hatched eggs only = inactive infection; no infection risk

Updated by Rick Speare
14 September, 1998