Hi!

I remember having head lice when I was younger...bad times!  I remember scratching my head all the time, but no matter how much I would do that, the infestation never ceased.  I had to have vile ammonia like stuff to get rid of them eventually.  I would suggest that scratching a certain side would infact help the lice in their quest for a meal by loosening up dead skin and oils and therefore prefered my right side (im right-handed) and your childrens left.  They have adapted; the ability to be almost untouchable without the aid of chemicals or electric combs but not a intuition of left and right.

Good question, Cheers

Deko.

My friend has always slept on her right hand side, always. She reckons this has made the hair on her right side thinner than her left.

Perhaps a similar thing is happening here, the hair is thinner on one side, or the child has been lying on one side. Making one side of the head more attractive to the lice.

Or, if the hair on one side was indeed thicker, it may make the eggs on that side harder to spot, creating an illusion of more eggs on one side.

I think this theory creates more questions than it answers im afraid.