MadSci Network: Medicine

Re: Is it true that head lice will not infest colour-treated hair?

Date: Mon Jan 19 22:28:37 2004
Posted By: Roy Costa, Faculty, Hospitality and Tourism Institute, Valencia Community College
Area of science: Medicine
ID: 1073702484.Me


Head lice and personal hygiene

Head lice are not a sign of poor hygiene, dirty hair or lack of parental 
care. Washing hair does not kill head lice, as they can survive under 
water for several hours. Anyone with hair - long or short, clean or 
dirty - can get head lice.

Head lice and disease

Head lice do not carry any disease. However they can make the skin itch 
and persistent scratching can cause skin infections.

Cleaning the house

It is not necessary to wash all the household linen, or to vacuum, scrub 
or spray the house with household insecticide, or to treat the dog or 
cat. Pillowslips may be soiled with lice debris such as droppings and 
moulted lice skins, so they should be washed on the first day of 

Why is cleaning not recommended?
• Head lice do not live in the environment. If they did live in the 
environment then they would be seen everywhere, like ants, and people 
would be infested all the time.

• Head lice are human parasites and need to feed from the scalp every few 
hours. They do not survive for more than a few hours away from the body 
as they quickly dehydrate.

• Head lice kept in a sealed jar may live a few hours longer due to the 
warmth and humidity of the container. (This is not the same as their 
normal environment and head lice will not reproduce in these different 

• Head lice do not leave the scalp unless they are dead, dying or have 
been deliberately removed. The blood supply of the scalp is their only 
food source.

• Head lice that fall off the hair at the end of their life cycle are not 
likely to lay eggs while dying. If they did, the eggs would not survive 
away from the necessary constant heat and humidity of the scalp.

• Head lice that have been deliberately removed from the hair would be 
unlikely to return since they cannot walk very well. Their curved legs 
and claws and are designed only for gripping and climbing along the hair 

‘Flying - Jumping - Swimming’ lice
Head lice cannot fly, jump or swim. They do not have the hind legs or 
wings needed to do so. They can run very fast along one hair to get onto 
another. Head lice can swing or ‘trapeze’ from one hair to another if 
hairs are very close and this may be mistaken for the insect ‘jumping’.
Eggs (‘Nits’)

Not every egg found on the hair at any given time will produce head lice. 
Only those within 1 cm of the scalp will hatch to produce more lice. Most 
eggs further out along the hair shaft will be already hatched. The rest 
will simply have died.

Vinegar and removal of eggs

The cement that glues eggs to the hair is extremely strong and cannot be 
removed by vinegar. Researchers have found that the structure of the 
cement is related to the structure of hair and can only be dissolved by 
strong acid. After the eggs have hatched the cement gradually breaks down 
and eggs are then much easier to detach.

Dye and Bleach

There is no evidence that dye or bleach kills or prevents head lice 
infestations, in the concentrations normally used. Therefore dyed or 
colored hair is no protection. Using these products to kill lice will 
cause injury to the scalp, burns to the scalp, loss of hair and other 
dangers and is definately NOT recommended.

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