How do you detect or diagnose head lice?
Head lice may be brought home after a person has had direct head-to-head contact with someone who has an active head lice infestation. This is most often a close family contact or friend. Lice may spread rapidly to others throughout the home because of the close contact of family members. Whenever one person in the family has been identified to have lice, everyone living in the home should be checked. Any friends, family members, or other people who have had close head-to-head contact with the infested person over the previous week should be notified so they can be checked for head lice as well.
Careful inspection of the hair and scalp is necessary to see if a person has head lice.
Supplies needed for a head lice inspection include:
- Time – The person who is inspecting for head lice needs to conduct a careful and thorough search. Times may vary, but this process may take over ten minutes per person.
- Strong source of natural light, high intensity lamp, or strong flashlight – Nits reflect ultraviolet light, so natural light (near a window or outside) are the best. If natural light is not available, convenient, or sufficient, a lamp (>60-watt bulb) or strong flashlight (LED recommended) can be used.
- Magnifying glass (with a light source if possible)(optional) – Nits are small and may be difficult for some people to see. Newly hatched and adult head lice are also tiny, crawl fast through hair, avoid light, and may be difficult to see in contrast with certain hair colors. A magnifying glass may assist in focusing on a small area and detecting movement. It may also be helpful for people with problems focusing at close distances.
- Fine-toothed comb (lice comb) or other disposable hair parting tool (optional) – To examine the base of the hair nearest the scalp, most examiners will need to use a tool to part and lift the hair. If more than one person is being inspected, new tools should be used for each individual. The inspectors should wash hands between checking individuals for general hygiene.
- Disposable gloves (optional) – There is no evidence showing that head lice are spread through hand contact; however, some organizations or facilities may mandate barrier precautions for hygienic reasons. If gloves are used, they should be changed between each inspection.
- Transparent tape (optional) – If a head lice infestation is suspected and the person conducting the inspection is having difficulty identifying the insect, transparent tape may be used to capture and seal the insect for further identification by someone trained to identify head lice.
Head lice are best identified by inspecting the hair and scalp for live lice or nits (eggs attached to the hair shaft close to the scalp). The standard for identifying head lice is finding a live louse on the head. Lice and nits are most often found at the nape of the neck and above and behind the ears.
- Carefully part the hair and examine the hair and scalp for nits or crawling lice.
- Begin by inspecting the nape of the neck and the area behind the ears. If nothing is seen in these areas, continue to inspect the rest of the head.
- Most recently laid nits will be opaque, white, shiny, and located on a hair shaft within one-quarter inch of the scalp. Empty nit cases are more visible and are dull yellow in color.
- Dandruff, hair casts, globules of hair spray, and scalp conditions such as psoriasis or eczema may easily be mistaken for nits. To differentiate between nits and other debris, remember that hair debris is easily detached or loosened from the hair shaft, and nits are firmly attached to the hair and are not easily removed. Nits are also usually found one-quarter inch or more from the scalp due to hair growth following the initial attachment. By the time the hair has grown sufficiently for the egg case to be one-half inch from the scalp, the egg has either hatched or is non-viable.
- Nits or lice in the eyelashes or eyebrows indicate possible infestation with other species of lice. Specimens should be submitted to a laboratory for full identification, and the case referred to a private physician or local health department, as a different form of treatment will be required.
Questions about identifying lice or nits should be referred to a health care professional familiar with head lice, such as a school nurse or local health department. Lice may be submitted to a laboratory in a clean/dry container or on a piece of transparent tape. Pieces of hair with possible nits attached may be snipped and submitted to a laboratory in the same manner. In Michigan, identification may be obtained through:
- Local or state health department
- Michigan State University Extension office
- Healthcare provider