Understanding Head Lice (Pediculosis Capitis)

Educational information for licetreatments.org. Not a substitute for medical care. If you’re unsure whether you have lice or symptoms persist after treatment, contact a healthcare professional. 

What are head lice?

Head lice (Pediculus humanus capitis) are tiny parasitic insects that live on human hair—most commonly on the scalp—and feed on small amounts of human blood. They can also be found on eyebrows and eyelashes in some cases. 

• Size & appearance: Adult lice are about 2–3 mm long (roughly sesame-seed sized) and can look tan/grayish; they move by crawling (they do not fly or jump).
  
• Who gets them: Anyone can get head lice. Infestations are not a sign of poor hygiene and are common among school-aged children because of close contact.
  

The head lice life cycle (in detail)

Head lice go through three stages:

1) Eggs (“nits”)

• Lice lay eggs that are firmly attached to hair shafts close to the scalp. 
  
• Nits can be mistaken for dandruff, but unlike flakes, they don’t brush off easily. 
  

2) Nymphs (immature lice)

• After hatching, nymphs look like smaller versions of adults and must feed on blood to survive. 
  

3) Adults

• Adult lice continue to feed and reproduce while living on the scalp and hair. 
  

Key point: Lice depend on the scalp’s environment to live and reproduce, which is why they are primarily a head-to-head contact problem.

How head lice spread

Head lice spread mostly by direct head-to-head contact, when lice crawl from one person’s hair to another’s. 

Less commonly, they can spread through sharing items that touch hair, such as:

• hats, headbands, helmets
  
• brushes/combs, hair ties
  
• scarves, towels, bedding 
  

What they don’t do

• They don’t fly or jump. They move by crawling. 
  
• Head lice are not known to spread disease the way some other parasites can.
  

Signs and symptoms

Some people have no symptoms, especially early on or with a first infestation.

Common symptoms include:

• Itching (pruritus): often due to an allergic reaction to bites 
  
• Tickling or a “moving” feeling in hair 
  
• Irritability or sleep trouble (lice can be more active at night) 
  
• Sores or scratch marks on the scalp from scratching
  

How to identify head lice accurately

Correct diagnosis matters because itching alone is not proof of lice.

Most reliable approach: find a live louse (nymph or adult), often using a fine-toothed nit comb and good lighting. 

Where to look:

• behind the ears
  
• at the nape of the neck
  
• along the hairline 
  

Important: Finding only nits does not always mean there is an active infestation. (Some nits may be old/empty.) Clinical guidance emphasizes careful confirmation before repeated treatment.

Myths vs facts (to reduce stigma)

• Myth: “Only people with poor hygiene get lice.”
  Fact: Lice infestations are not related to cleanliness; lice simply need access to a human scalp. 
  
• Myth: “Lice live on pets.”
  Fact: Head lice are human parasites; pets are not their normal host. 
  
• Myth: “Kids must be sent home immediately and be ‘nit-free’ to return.”
  Fact: Public health guidance has moved away from strict “no-nit” policies; lice are not considered a reason for immediate exclusion in many recommendations.
  

Health impact and complications

Head lice are associated with limited morbidity, but they can cause:

• itching and discomfort
  
• skin irritation and secondary infection risk from scratching
  
• stress, stigma, missed school/work, and caregiver anxiety
  

Prevention: what actually helps

Prevention focuses on reducing opportunities for lice to crawl to a new host:

• Avoid head-to-head contact during play, sleepovers, selfies, sports huddles 
  
• Don’t share combs/brushes, hats, helmets, scarves, hair accessories 
  
• If someone in the household has lice, consider checking close contacts and following evidence-based treatment guidance
  

Treatment overview (high-level)

licetreatments.org may cover treatments in dedicated pages; for context, major health authorities note that head lice can be treated with over-the-counter and prescription options, plus combing. 

If symptoms persist, live lice remain after proper use, or you’re treating eyelashes/eyebrows, seek medical advice.

Home and environment: what’s reasonable to clean

Because lice survive best on the scalp, cleaning efforts should be targeted rather than extreme.

Common guidance includes focusing on items with recent head contact, such as:

• pillowcases, bedding, hats, scarves
  
• hair brushes/combs (clean as directed)
  
• items used by the affected person