head lice the facts

Head lice - the facts

The Pediculus humanus is a small, wingless insect with a flattened body about 3 mm long (1/8 inch). It has a claw on the end of each leg that helps it cling to the hair of its human host. Once a day, females lay whitish eggs, often called nits, attaching them to the hair with a sticky substance until they hatch in about a week. Head lice infest people who bathe often as well as those who do not, leaving itchy red spots on the host scalp. They may be particularly prevalent in school age young children who tend to have more head to head contact than teenagers and adults who tend to be more reserved about close physical contact.

The life cycle

Egg stage – approximately 8 days.

Live eggs are opaque in colour, clear eggs have already hatched. Live eggs near to hatching may 'pop' if squeezed.

Eggs are usually found cemented to within 1.5 cm of the scalp, hatched eggs will be found further away. The sticky substance used by the lice to cement eggs to hair shafts is called chitin – vinegar has been found to slightly soften the glue to make removal of the eggs easier.

After hatching, the louse takes 3 weeks to grow into an adult. Lice are grey to grey-brown in colour and are very difficult to see at first. As they grow they become more visible and easier to trap between the teeth of a fine tooth comb.

Female adults lay eggs once a day.

Treatments

Commercial head lice products: There are several different types of insecticide products available. Resistance to insecticides in head lice is common, although they may not be resistant to all types of product.

You will know if the head lice are resistant to a particular compound if, after a correct treatment, the head lice will still be alive on close examination.

If the treatment has worked, all the head lice will be dead after 20 minutes

Major compounds available:

Pyrethrins – a natural pesticide contained in some flowers including chrysanthemums – can be toxic in excess.

Synthetic pyrethrins

Permethrin – less toxic than pyrethrin.

Lindane-based products – more toxic than pyrethrin and permethrin.

WARNING – May also be carcinogenic.

Malathion – generally considered safer than lindane WARNING – Flammable.

Organophosphates

Herbal – including essential oils. In view of the toxicity of other chemical preparations, essential oils and herbal products are more desirable. If used in conjunction with combing methods, they have also been proved to be as effective.

Combinations of herbal and pyrethrins.

IMPORTANT – No commercially available treatment will kill all the eggs: a second treatment is always necessary. Eggs which were not killed after the first treatment will hatch up to 8 days afterwards. These need to be killed before they reach the adult egg-laying stage between 2-3 weeks. A second treatment at 8 days will kill all newly hatched lice.

Preventative methods

Regular fine-tooth combing of the hair will remove any live lice before they have the opportunity to lay eggs. Metal combs are best as the teeth do not bend and miss eggs cemented to the hair. Metal flea combs made for animals are just as effective as the more expensive combs available from chemists. Pale coloured combs are also better than dark combs as you are more able to see the darker coloured lice on the comb.

The louse clings on to the hair shaft with its claws. By using a conditioner the hair is made more slippery, loosening the louse’s grip to the hair. Combing out at this stage is particularly effective.

Shampoos with added lice compounds are not effective as they are too dilute and will not remain on the hair long enough.

Lice can remain alive for up to 72 hours after they have left the human host. Therefore they can remain on pillows, bed linen, combs, clothes and towels, able to re-infest. After lice have been treated, it is important to back-up treatment with a clothing and linen washing routine.

How do I tell it is a louse egg? Louse eggs are cemented to the hair, they are difficult to remove and have to be slid up the hair shaft. Ordinary dandruff and debris from other fungal infections will come away from the hair and scalp more easily.

How do insecticides work? Insecticides attack the nervous system of the lice. The active compounds may also be toxic to humans in the same way if used frequently. Frequent use also encouraged insecticide resistance in the lice.

What if the lice are resistant to treatment? Try another product using a different compound.

Resistance to permethrin products is the most common, particularly in people who have had multiple treatments.

Using essential oils

Many publications list several essential oils suitable for treating head lice. Of these, Veal (1996) used laboratory tests to assess their effectiveness in killing both eggs and live lice. She arrives at the following: Oregano, aniseed and cinnamon leaf – kills 100% of adults and eggs. Tea tree – 83% eggs, 93% adults. Veal also states that the active ingredient in the essential oils used are mostly the phenols, ketones, oxides or aldehydes, so oils high in these chemicals will be the most effective. These would include Bergamot, Spearmint, Niaouli, Petitgrain, Pennyroyal, Ravenscara, Benzoin, Caraway seed, Roman chamomile, Eucalyptus (citriodora and smithii), Clary sage, Jasmine, West and East Indian lemongrass, and Spanish marjoram.

The most effective method of application was using a high concentration of essential oil in alcohol (alcohol makes the insect skins more permeable to the insecticide properties of the essential oil solution).

E.g.: 50 mls alcohol (vodka) to 10 drops essential oil rubbed into the scalp/hair, then left overnight.

The solution can then be washed off with shampoo, after which 2 mls of the original mix is added to a rinse solution of 50 ml vinegar and 50 ml water. The treatment should be repeated after 7 days and fine combing between treatments is essential.

CAUTION: oils high in ketones need to be used with care in pregnancy and aldehydes used in excess may irritate the skin (Price 1999, p31-32). There are other specific cautions associated with high concentrated use of some of these oils so they should only be used under the supervision of a trained practitioner.

Treatment with Carrier oil

Sue Seale (http://fly.hiwaay.net/~sseale/ftest.html) offers an alternative to pesticide treatments by stating that she is reasonably convinced that in the majority of situations, a carrier oil has sufficient suffocating capabilities to make almost any mixture of essential and carrier oil effective in killing lice (although possibly not the eggs). She states that any combination of essential oil and carrier would also be more pleasant to use. Veal certainly supports this idea by saying that Jojoba oil may be particularly effective (as well as some other carrier oils) because the insect cuticle is soluble to lipids and lipid compounds (a major constituent of carrier oils). Further evidence from Price et al. (1999) supports the effectiveness of penetration using lipid-based compounds (carrier oils), into which essential oils have become soluble. Using a carrier oil with essential oils to treat head lice has an added advantage against using an alcohol base because carrier oils are fixed oils and do not evaporate, whereas alcohol –based preparations evaporate quickly, along with the highly volatile essential oils dissolved in them.

Some parents are understandably reluctant to use the powerful neuro-toxins contained in pesticide-based preparations, particularly now lice are becoming resistant to such chemicals. The evidence examined proves the effectiveness of certain essential oils against lice and eggs as a more acceptable treatment. The ideal medium in which to apply the oils seems to be in a lipid-based compound commonly regarded as a carrier oil to suffocate the lice and enable maximum penetration for the essential oil to do its work.

A blend for success

10 ml Jojoba

40 ml Extra virgin cold pressed olive oil

10 drops Cinnamon leaf (Cinnamonum zeylanicum), reported as being anti parasitic by both Lawless and Veal.

5 drops Tea tree (Melaleuca alternifolia) due to its reported insecticide effect yet still being a safe oil. Oils must be bought from a reputable source to ensure their anti-parasitic qualities have not been compromised by the addition of synthetic chemicals.

Method

Massage half the blend into the hair and scalp, leave overnight under a shower cap.

Shampoo and condition, using a fine tooth comb to comb out the debris, wiping each time onto a tissue. Repeat after 8 days.

CAUTION: Wash immediately should any irritation occur on the scalp or in the eyes. Essential oils can be made soluble in milk, then rinsed thoroughly.

Top of page

Fact sheet to print and use as you wish

References and information

Lawless J (1999) The Encyclopedia of Essential oils Shaftsbury, Element Books Limited

Price L,. Price S (1999) Aromatherapy for Health Professionals London: Churchill Livingstone

Pollack RJ, Kiszewski A, Armstrong P, Hahn C, Wolfe N, Rahman HA, Laserson K, Telford SR III, Spielman A. Differential Permethrin Susceptibility of Head Lice Sampled In the United States and Borneo. Archives of Paediatrics and Adolescent Medicine. 1999; 153:969-973. An abstract of their article is available on the American Medical Association's web site at http://www.ama-assn.org/public/journals/ajdc/.

Seale S (updated 5/16/00) The great head lice information page http://fly.hiwaay.net/~sseale/ftest.html

Speare R (April 4 2000) Dept of Public Health and Tropical Medicine James Cook University http://www.jcu.edu.au/school/phtm/PHTM/hlice/hlinfo1.htm

Veal L (no date) Head lice http://www.wingedseed.com/Agora/Lice_page.htm