A fine tooth comb, sometimes called a fine-toothed comb, is merely a hair comb that has small, narrow teeth that are set closely together. For centuries, people used such combs for the unglamorous purpose of removing the eggs of lice (nits) from their hair, though people with shorter hair also found they were helpful in simply combing the hair. An example of the fine tooth comb today for hair styling is the traditional black comb, about 3-4 inches (7.62-10.16 cm), that many men with short hair use as their main styling tool. It tends to be less effective on longer hair that is very thick, and may pull and hurt if you’re trying to use it to get out snarls.
The fine tooth comb, as used for the removal of lice eggs, is often sold separately as a lice comb. You can also find fine-toothed combs called flea combs for cats and dogs. Even after using a lice shampoo, nits or lice eggs tend to adhere to the hair shaft, and it’s important to try to removed as many as possible. By combing through the hair with a fine tooth comb, you can remove most nits. This is also a good way to check for lice, though you can get confused if the comb removes dandruff too. To really check whether you have lice or dandruff, watch carefully as you pull the comb through small sections of the hair, and see if any of the flakes give slight resistance to being removed, which indicates they may be nits.
The expression of “going over things with a fine toothed comb” was first used in the late 19th century. It was often linked to detection or police work. Just as a person would use a fine tooth comb to examine minute sections of hair, investigatory proceedings began to go over the minutia of each crime scene. Today the expression can apply not just to criminal investigation, but also to a very detailed approach to anything. An editor might go over a book or article with a fine tooth comb to check for any tiny mistakes, as might a teacher use a similar approach when he/she is examining a student’s work. Computer programmers also focus on tiny mistakes that might occur in data entry and programming, and referencing the comb as used for lice, check for any “bugs” in their programs.