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Basic

Life cycle

Head lice live in three stages: eggs/nits, nymphs and adults.

Head lice are “oviparous”, meaning they lay eggs, and embryos develop almost entirely outside the mother (and inside the egg).

Eggs live attached to hair on the scalp. They look yellow but are generally too small to see. In this life cycle stage, head lice do not feed on human blood.

Eggs turn into nymphs after about a week and are then fed every few hours. The nymph’s body turns dark red after feeding. Nymphs survive for eight to nine days and then transition to adults, which can live for a month.

Read more about the biology of the louse and the life cycle of the louse.

Mobility

Head lice cannot fly, but they can crawl into sweaters, towels, hair accessories and carpets, which is generally how infection occurs. It is possible for lice to survive for several hours in water (such as in a pool), but this type of person-to-person transmission is rare.

Health concerns and treatment tips

According to the Centers for Disease Control and Prevention, lice are not known to transmit any disease and are therefore not a public health hazard. However, head lice infestations require treatment and can be prevented. Follow these principles in your treatment plan:

• Do not treat family members who do not have head lice. Treat for head lice ONLY when a person has them.
• Check everyone in the family with a good quality lice removal comb.
• Avoid pesticide-based shampoos.
• Shampoo hair with normal shampoo.
  • Use clips to divide wet hair into small sections, working with one section at a time.
  • Comb from scalp, place lice and eggs in a bowl of soapy water.
  • Some people report that using conditioner and leaving it in the hair makes the process easier.
  • Use a good quality fine toothed metal comb.
• Do not use environmental sprays for lice – they are unnecessary and can pose a health risk if used incorrectly.
  • Lice infect people, not the home.
  • They are human parasites. Lice cannot live without human blood for more than 24 hours.
  • Nites will not live unless they are given a meal of human blood as soon as they hatch.
• Vacuum carpets and upholstered furniture to remove hair with attached nits and any lice crawling off the infested person.
• Place bedding, pillows, stuffed animals and similar items in a dryer for 30 minutes on high heat to kill both live lice and nits.
  • Lice jump or don’t jump. They crawl and cling.
  • If a louse comes off the head and is left on a pillow, headrest, or hat, the louse can infect another person who places the head in that area. Vacuuming will catch these escapees.
  • Experts used to suggest wrapping items such as stuffed animals for several weeks to help control infestations, but this is now recognized as unnecessary.
• Do not treat family pets for lice with insecticidal shampoo. It is potentially harmful (to both humans and pets). Lice cannot live on pets, so there is no need to fear that lice may be hiding on your dog, cat or guinea pig.
• Do not use head lice treatments as a preventative measure. Head lice cannot be safely or effectively prevented by washing with either chemical or alternative treatments.
• Practice early detection by doing weekly head checks with a good quality comb. Early detection and removal of live lice or nits can keep head lice problems to a minimum. “It only takes a few minutes,” says Bonnie Byers, parent of four. “I check around the ears, the back of the neck, around the forehead and where the hair is parted. Lice seem to like these areas the best.”

Additional resources