Head Lice Treatment FAQ

If the treatment for head lice doesn't seem to be work, does this mean the lice are resistant and I need a different treatment?

The following are several common reasons why treatment for head lice may fail sometimes:

1. Misdiagnosis. The symptoms are not caused by an active head lice infestation.
2. Applying the treatment to hair that has been washed with conditioning shampoo or rinsed with hair conditioner. Conditioners can act as a barrier that keeps the head lice medicine from adhering to the hair shafts; this can reduce the effectiveness of the treatment.
3. Not following carefully the instructions for the treatment that is used. Some examples of this are not applying a second treatment if instructed to do so, or retreating too soon after the first treatment before all the nits are hatched and the newly hatched head lice can be killed, or retreating too late after new eggs have already been deposited.
4. Resistance of the head lice to the treatment used. The head lice may have become resistant to the treatment. If the treatment used does not kill the head lice, your health care provider and pharmacist can help you be sure the treatment was used correctly and may recommend a completely different product if they think the head lice are resistant to the first treatment.
5. Reinfestation. The person was treated successfully and the lice were eliminated, but then the person becomes infested again by lice spread from another infested person.
   Sometimes reshampooing the hair too soon (less than 2 days) after correctly applying and removing permethin can reduce or eliminate any residual (continued) killing effect on the lice.

Is there a treatment recommendation for certain age groups?

Before treating young children, please consult the child's doctor, or the health department for the recommended treatment based on the child’s age and weight.

Are there any side affects from using these chemical treatments for head lice?

Treatments for head lice are generally safe and effective when used correctly. Some treatments may cause an itching or a mild burning sensation caused by inflammation of the skin on the scalp. Most products used to treat head lice are pesticides that can be absorbed through the skin. Therefore, all medicines used for the treatment of lice should be used with care and only as directed.

Is it necessary to remove all the nits?

Removal of all nits after successful treatment with a pediculicide is not necessary to prevent further spread. Removal of nits after treatment with a pediculicide may be done for aesthetic reasons, or to reduce diagnostic confusion and the chance of unnecessary retreatment. Because pediculicides are not 100% ovicidal (i.e. do not kill all the egg stages), some experts recommend the manual removal of nits that are attached within 1 cm of the base of the hair shaft.

Where can I go to have the nits removed from hair?

CDC does not make recommendations about businesses that may offer such services. Your health care provider or local health department may be able to provide additional guidance. Removal of all nits after successful treatment with a pediculicide is not necessary to prevent further spread of head lice. Removal of nits after treatment with a pediculicide may be done for aesthetic reasons, or to reduce diagnostic confusion and the chance of unnecessary retreatment. Because pediculicides are not 100% ovicidal (i.e. do not kill all the egg stages), some experts recommend the manual removal of nits that are attached less than1 cm of the base of the hair shaft.

Why do some experts recommend bagging items for 2 weeks?

Head lice survive less than one or two days if they fall off the scalp and cannot feed. Head lice eggs (nits) cannot hatch and usually die within a week if they do not remain under ideal conditions of heat and humidity similar to those found close to the human scalp. Therefore, because a nit must incubate under conditions equivalent to those found near the human scalp, it is very unlikely to hatch away from the head. In addition, if the egg were to hatch, the newly emerged nymph would die within several hours if it did not feed on human blood.

However, although rarely necessary, some experts recommend that items that may be contaminated by an infested person and that cannot be laundered or dry-cleaned should be sealed in plastic bag and stored for 2 weeks to kill any lice that already are present or that might hatch from any nits that may be present on the items.

Should my pets be treated for head lice?

No. Head lice do not live on pets. Pets do not play a role in the spread of head lice.

Should household sprays be used to kill adult lice?

No. Using fumigant sprays or fogs is NOT recommended. Fumigant sprays and fogs can be toxic if inhaled or absorbed through the skin and they are not necessary to control head lice.

Do I need to have my home fumigated?

No. Use of insecticide sprays or fogs is NOT recommended. Fumigant spray and fogs can be toxic if inhaled or absorbed through the skin and they are not necessary to control head lice.

Routine house cleaning, including vacuuming of carpeting, rugs, furniture, car seats, and other fabric covered items, as well as laundering of linens and clothing worn or used by the infested person is sufficient. Only items that have been in contact with the head of the infested person in the 48 hours before treatment need be considered for cleaning.

Should I have a pest control company spray my house?

No. Use of insecticide sprays or fogs is NOT recommended. Fumigant spray and fogs can be toxic if inhaled or absorbed through the skin and they are not necessary to control head lice.

Routine vacuuming floors and furniture is sufficient to remove lice or nits that may have fallen off the head of an infested person.

Will laundering kill head lice?

Washing, soaking, or drying items at a temperature greater than 130°F can kill both head lice and nits. Dry cleaning also kills head lice and nits. Only items that have been in contact with the head of the infested person in the 48 hours before treatment should be considered for cleaning.

Although freezing temperatures can kill head lice and nits, several days may be necessary depending on temperature and humidity; freezing is rarely (if ever) needed as a means for treating head lice.