How much blood do head lice drink and are they a danger?

How much blood do the little suckers drink?

Not much!

The amount of blood drunk by a head louse in a single feeding session is very small - from 0.0000387 ml to 0.0001579 ml.

Are they a danger in causing ongoing blood loss?

In general "No!". However, it depends how many lice a person has and their iron
status. The risk we looked at is for iron deficiency anaemia. The typical infected person
has less than 10 lice and there is no risk of anaemia. However, a heavily infected person
(thousands of lice) with a marginal iron status may have their condition made worse
by head lice.

How much blood will my child lose?

Use the calculator below to work out how much blood (in theory) that those
suckers will extract. You can use this in 2 ways:
  1. If you know how many lice are present (by using
    conditioner and comb technique
    ), enter a number into the ANY TYPE box.
  2. If you are a whiz and can identify the stages of some lice (NYMPHS) and sexes of the
    adults (FEMALES, MALES), enter these separately, but don't count them again in
    the ANY TYPE total. Adult female lice drink more than males and nymphs.

Number of Feeds per Day - research has not yet determined how many blood meals
a louse takes per day when a host is constantly available. However, it is known
that 3 blood meals is sufficient to keep lice colonies alive. Number of feeds per day equals

A click on any of the buttons below will recalculate all values

Enter number of
lice found below
Click to
This is the
total blood drunk per day

This equates to:

blood per day (ml) or

blood per week (ml) or

blood per year (ml)


Speare R, Canyon D, Melrose W. Quantification of blood intake of the head louse, Pediculus humanus capitis. International Journal of Dermatology 2006;45:543-546

Created by Deon Canyon, David Podger and Rick Speare
Updated 26 January 2013

Looking directly into the mouth of a head louse. Four stylets are visible. These are used to cut into a capillary and form a tube to suck out blood. (Scanning electron micrograph)