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

Rick Speare and Deon Canyon
Vector Control and Repellent Research Group
School of Public Health, Tropical Medicine and Rehabilitation Sciences, James Cook University, Townsville. 4811.

How much blood do the little suckers drink?

Not much! Our group has calculated how much blood head lice drink. See the paper Quantification of blood intake of the head louse: Pediculus humanus capitis. International Journal of Dermatology 2005. 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
calculate		 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)

[Head lice Information Sheet] [Head lice - Additional Information]

Created by Deon Canyon, David Podger and Rick Speare
Updated 9 May 2005