What happens if you have head lice and you can't get them all out because a lot of them have spreaded too much, then?

Call your doctor. Lice can be hard to eradicate because they can become resistant to medications available at the grocery store. Discuss with your doctor- there are prescription options. Consider cutting your hair short which can make it easier to remove the insects and eggs. Have someone help you - you need a fine tooth comb and patience to remove all the eggs and insects from every area of scalp. Repeat often. .