There are several types of lice: the head louse, or Pediculus humanus capitis, is a parasitic insect that can be found on the head and, less commonly, the eyebrows and eyelashes of humans. It feeds on blood and moves from one head to another.
It is the cause of scalp pediculosis (head lice infestation), which is the most common contagious disease in schools after respiratory infections.
Absolutely not! Contrary to popular belief, having lice does not mean one lacks hygiene. The louse is simply a tenacious parasite that has been particularly well adapted to humans for centuries. It settles on both clean and neglected hair. It makes no distinction between races or social classes.
There are three stages in the life cycle of a louse: the egg (also called a nit), the nymph, and the adult. The appearance of the louse will vary depending on its stage of development.
Nits: They resemble tiny dots that can be yellow, beige, or brown before hatching. After hatching, the shell looks like a white or light dot. Nits are firmly attached to the hair root (about 0.5 cm maximum from the scalp) and are very difficult to remove. They are typically found in the warm and humid areas of the scalp (mainly around and behind the ears and at the back of the head near the neckline). It is not uncommon to confuse nits with dandruff, so if in doubt, try removing them with your fingers. If you cannot easily remove them, they are probably nits and not dandruff.
The nit typically takes 5 to 10 days to hatch.
Nymphs: This stage lasts about 7 days during which the baby louse will transition from the larva stage to the adult louse stage. During this time, nymphs begin to move and look similar to adults, but are a bit smaller and their color can vary. Nymphs can be black, light, or red. Just like adult lice, nymphs need to feed on blood in order to reach their full size and survive.
Adult lice: They are easier to spot as they are larger (about the size of a sesame seed, between 2 and 4 millimeters). Their color can vary (grayish-white or reddish-brown) and they typically move at the root of the hair.
Excluding the 5 to 10 days they spend in the egg, lice can live from 40 to 45 days on a head. As parasites, they feed on human blood several times a day.
During their life cycle, a female louse can lay between 150 and 300 eggs. An untreated infestation can thus last for months or even years.
If they are removed from their food source – for example, by being brushed out of your hair or by your hand – they can survive for 24 to 48 hours. If they do not find human hair to settle on during this period, they will die.
In addition to finding a nymph or adult louse living on the scalp, other signs should alert you and prompt you to carefully inspect the person’s hair:
- Tickling sensation, feeling like something is moving on the scalp
- Severe itching, generally caused by an allergic reaction to louse bites
- Irritability and difficulty sleeping; lice are most active in the dark
- Wounds on the head caused by scratching.
No, four out of five infested people do not experience itching, which is why some infestations can last for weeks or months before being detected.
No! Lice cannot jump, swim, or fly. They move using six legs equipped with claws that allow them to grip the hair effectively and move. Without strands of hair to cling to with their claws, they have a lot of difficulty moving. However, since they move quickly on hair, they can easily reach your scalp if your head comes into contact with infested hair.
The main way to catch lice is by placing your head directly in contact with the head of an infested individual. The infestation will not necessarily spread with head-to-head contact, but lice have a better chance of moving from the infested person’s hair to yours.
Less frequently, lice are transmitted between people through indirect contact and items such as hats, ties, scarves, cushions, pillows, etc. However, this type of transfer is quite rare, with probably less than two percent of cases being transmitted through the environment. This is because lice cannot survive more than 48 hours off a head. They are designed solely to live in human hair. They generally do not like to leave the protective environment they have in the hair.
No one is immune. Children between the ages of 4 and 12 are the most affected (with a majority of cases among girls), but increasing cases of infestation are being seen in teenagers. Pajama parties, the habit of gathering around a smartphone screen to take a group photo or watch a video together, are all factors that facilitate the transmission of lice from one head to another.
Teachers, parents, grandparents, nannies… In short, anyone who has close contact with infested children can themselves become infested.
Lice do not survive long if they fall off a person’s head and cannot feed. Don’t panic! You do not need to spend much time or money cleaning your house. Follow these steps to prevent re-infestation of lice that have accidentally fallen from hair and settled on clothing, bedding, or furniture.
- Wash and machine dry the clothes, bed sheets, and other items the infested person has worn or used in the two days before treatment, using the hot water wash cycle (60 degrees Celsius) and the high heat drying cycle. Clothes and items that cannot be machine-washed can be dry-cleaned OR sealed in a plastic bag and stored for two to three days.
- Soak combs and brushes in hot water (at least 60 degrees Celsius) for 5 to 10 minutes or change the brush.
- Vacuum the floor and furniture, especially where the infested person has lain or sat. However, the risk of infestation from a louse that has fallen on a carpet or furniture is very low. Head lice survive less than two days if they fall off a person and cannot feed; nits cannot hatch and will typically die within a week if they are not kept at human scalp temperature.
- Do not use aerosol insecticides: they can be toxic if inhaled or absorbed through the skin.
The risk of re-infestation is much higher if the person who has been treated comes into contact with an infested person again. This is why it is important to ensure that all family members have been checked. Certain habits can also help prevent infestations, such as tying hair back when going to school, explaining to children that head-to-head contact should be avoided, teaching children to store their hats and scarves inside their jacket sleeve, and regularly checking their hair with a lice comb.