What causes the itch of head lice?

When a head louse sucks blood, it injects some of its saliva into the wound, which prevents the blood from clotting.
It does this to keep the blood flowing well so that it can drink enough blood.
It's this saliva that can cause itching, provided you have an allergic reaction to it.

In the case of an allergic reaction, it can take about 2 weeks after the initial infestation before you begin to feel the itch. This is referred to as the incubation period.
The itching can even persist for 2 weeks after the infestation has been eliminated.

Approximately 53% of people are not allergic, and they don't experience any itching, even if they have hundreds or thousands of lice.

The annoying itching sensation can sometimes disappear for a while and later return.
Especially in the evening and at night, more people complain about itching.
The degree of itching can also increase as more lice are present on the head.
More lice means more lice bites, and for those who experience the typical itching from lice bites, this means more itching.

In people with long hair, it's often observed that lice prefer the skin on the neck, where they descend along the long hairs.
Once they've fed, they climb back up to the warm scalp, leaving behind clearly visible lice bites that can be quite itchy.

Does itching necessarily mean I have head lice?

No, itching can have many causes.
Changes in the weather, a dry scalp, reactions to hair care products, and even some lice treatments can actually cause itching because they may not always be gentle on the scalp.

And then there’s the psychosomatic type of itching, the kind we all sometimes experience simply because we think about lice or hear people talking about it.
Psychosomatic itching feels exactly the same as physical itching, namely the sensation of crawling lice on your skin.

But the ironic part is that you can't actually feel lice crawling!
Over the thousands of years they've been living on our heads, lice have evolved to be completely unfelt and unnoticed in our hair.
The only physical itching you might feel is from the lice bites, the reaction to their saliva.

So people can mistakenly think they still have head lice just because they continue to experience psychosomatic itching.
This itching persists precisely because they keep thinking they are infested.
It creates a vicious cycle perpetuated by this incorrect self-diagnosis.

However, sometimes, it has a deeper cause, namely when someone suffers from Ekbom Syndrome.
These are people with prolonged (itching-) complaints who are irrationally convinced that these are caused by lice (or other parasites) without actually having lice.
More about this can be found on our page, specially dedicated to the “Ekbom Syndrome”.