What is a head louse?

A head louse is a parasite that lives exclusively on humans.
A head louse cannot survive on an animal; you cannot get or transmit head lice through contact with animals.

An adult louse is approximately the size of a sesame seed and is brownish-gray of color.
Lice have a flat body with 6 legs and 2 small antennae.
The female is slightly larger than the male and can be distinguished by the shape of her rear end.
 

Lice have no wings, so they cannot fly.
They also lack legs designed for walking on surfaces or for jumping.
They can only climb from hair to hair.
However, they are highly skilled climbers. Using a few legs to grasp one hair, they use the other legs to sense where the next hair is to climb onto.
This allows them to move over distances of up to 30 centimeters, so from one side to the other side of your head, per minute.

 

They make use of the claws located at the ends of their six legs, which fit perfectly around a hair and allow them to hold on tightly to your hair.
So, even when you brush or comb your hair, run your hands through it, or rub your head against your pillow, a louse won't fall out of your hair as a result.
 

Lice do not have lungs like mammals. Like most insects, lice breathe through small openings on the sides of their bodies called tracheae.
 

They can close these openings to hold their breath for up to 8 hours.
This is why lice do not drown when you shower, wash your hair, or swim.

A head louse feeds on its host's blood approximately 5 times a day. They possess a piercing mouthpart that allows them to pierce the skin without being felt.
Lice introduce a bit of their saliva into the puncture wound to keep the blood flowing and to ensure they can drink  enough.
 

In addition to the host's blood, a louse also requires the body heat and high humidity of the host's scalp.
The thicker the hair, the more sultry it is, the better the louse can thrive.
It is primarily the combination of warmth and moisture where both a louse and its eggs thrive.
 

What is a nymph?

The newly hatched lice are called nymphs.
In the beginning, they are as small as a nit; to the naked eye, they appear as moving specks of dust.



Lice have an exoskeleton, just like a crab or a lobster.
As the (soft inside of the) young nymph grows, the external rigid shell eventually becomes too small.
To free themselves from the constricting "jacket", the nymph molts. 
The nymph undergoes this molting process three times in a period of ten days, after which it becomes an adult louse.



When a recently molted nymph sheds its exoskeleton, it is almost transparent, allowing you to see the consumed blood, making the nymph appear red. 



Nymphs are usually found lying flat on the scalp because it's warm and humid there, which is exactly what the nymph needs.
During a combing treatment, nymphs are often missed because they slip through the tapered points of the nit comb teeth.
This issue can be addressed by combing with the ‘Comb Cream’, which is highly suited for this job because nymphs and lice get stuck into this cream and are then combed out, cream and all. 
 

What is a nit?

The eggs of head lice are called nits.
A nit is only 0.8 millimeters long.
A female head louse only needs to be fertilized once by a male and can lay between 100-150 eggs in her lifetime.


 

Nits are attached extremely firmly to the hair.
The adhesive is not only strong but it is also applied all around the hair shaft, preventing the nit from being pulled sideways away off from the hair.
Only with a very good nit comb it is possible to detach the nit and slide it off of the hair.
Nits can remain firmly in the hair for months, up to a year, even when the egg has already hatched or when the embryo in the egg has died.

In the picture below, you can see the nit with a "tail".
This "tail" is the adhesive that has surrounded the hair shaft like a casing.



The louse always lays its eggs very close to the hair roots, where they can develop into young lice thanks to the warm and humid environment of the scalp.
Eggs that are located more than a few millimeters away from the scalp have been laid longer than 10 days prior and therefore cannot contain live embryos, as eggs always hatch within 10 days.


 

Fortunately, not all nits hatch, which is exactly why the louse lays so many of them, to ensure its survival.
However, it's important to kill or remove each viable nit to eliminate an active infestation, unless you consistently comb with the right tools for a minimum of 14 days.
Doing this, you continuously remove newly hatched lice (nymphs) before they can lay new eggs, eventually breaking the cycle.

Lice treatments often only kill some of the eggs, and nits also frequently slip through the teeth of nit combs.
Therefore, it's essential to use a high quality nit comb with teeth that do not spread apart.
 

What is the difference between brown and white nits?

A nit is a transparent egg containing an "unborn" louse: the embryo.
The embryo is brown in color, giving the nit a brown appearance.
After 7 to 10 days, the egg hatches, leaving behind an empty, transparent shell that appears white.

So, white nits are empty eggs, and brown nits are eggs with a (potentially live) embryo inside. 


 

Sometimes you may also see eggs that are partially filled and partially empty. These are nits with an embryo that did not fully develop and has died.
A dead embryo, of course, cannot hatch from the egg and remains inside, where it shrivels over time.
This explains the empty parts in the egg.

Frequently, dandruff is mistaken for white nits.
There is even a type of dandruff that clings around the hair shaft like a cylinder.
Because this type of dandruff closely resembles white nits, it's also referred to as Pseudo-Nits (see the photos below).

 

How can I tell if a nit is still viable?

A nit is possible viable if it meets all of the following 3 criteria:

1. The nit is located within a few mm of the scalp.
2. The nit is firmly attached to the hair.
3. The nit is entirely light to dark brown in color.


 

For more information on determining if you have an active head lice infestation, you can visit our Diagnosis page.