Causes and Transmission
Pediculosis capitis is caused by the head louse, a tiny wingless insect that lives on the human scalp and feeds on blood. The primary way these parasites spread is through direct head-to-head contact with an infested person. This allows the lice to crawl from one person's hair to another. They cannot fly or jump. Although less common, transmission can technically occur through sharing personal items like hats, scarves, brushes, or combs, but lice survive only a short time away from the human scalp.

Risk Factors
Anyone can get head lice, but certain groups are at higher risk due to their behavior and environment. Age is the most significant factor; preschool and elementary school-aged children are most frequently affected because they often play closely together. Living in crowded conditions or sleeping in the same bed as an infested person also increases the risk. Personal hygiene and cleanliness are not risk factors; lice prefer clean hair just as much as dirty hair.

Prevention
Preventing head lice primarily involves reducing opportunities for direct contact. Parents and caregivers can:

• Encourage children to avoid head-to-head contact during play and other activities
• Advise against sharing clothing, such as hats, scarves, coats, sports uniforms, or hair ribbons
• Suggest not sharing combs, brushes, or towels
• Disinfect combs and brushes used by an infested person by soaking them in hot water for at least 5 to 10 minutes

Signs and Symptoms
The most common symptom of head lice is itching on the scalp, neck, and ears. This itching is an allergic reaction to louse bites and saliva, though it may take four to six weeks to appear after the first time a person is infested. Other signs include:

• A tickling feeling or sensation of something moving in the hair
• Irritability and difficulty sleeping, as lice are often more active in the dark
• Sores on the head caused by scratching, which can sometimes become infected

Diagnosis
Diagnosis is confirmed by finding a live nymph or adult louse on the scalp or hair. Because lice move quickly and avoid light, they can be difficult to see. Finding nits (eggs) firmly attached to the hair shaft within a quarter-inch of the scalp suggests an infestation, but nits alone do not always indicate an active case, as they may be old or hatched empty shells. Health care providers or parents often use a fine-toothed louse comb (wet combing) to carefully examine the hair, which is generally more effective than visual inspection alone.

Differential Diagnosis
Head lice are often confused with other conditions that leave debris in the hair. Clinicians must distinguish live infestation from:

• Dandruff (seborrheic dermatitis)
• Residue from hair products like spray or gel
• Dirt or sand particles
• Hair casts (tubes of skin that slide along the hair shaft)
• Scabs or other skin conditions

Medications
Treatment typically begins with over-the-counter (OTC) medications containing pyrethrins or permethrin. These are insecticides applied to the scalp to kill the lice. In some regions, lice have developed resistance to these chemicals. If OTC treatments fail, doctors may prescribe stronger medications such as malathion, benzyl alcohol, spinosad, or ivermectin (topical or oral). It is crucial to follow the package instructions precisely regarding how long to leave the medication on and whether a second treatment is needed days later to kill newly hatched nymphs.

Manual Removal (Wet Combing)
Removing lice and nits by hand is a safe, non-chemical management strategy, often used in conjunction with medication or for young children who cannot use certain drugs. This involves wetting the hair, applying a lubricant like conditioner, and using a special fine-toothed comb to physically remove insects and eggs. This process requires patience and must be repeated every few days until no lice are found for two weeks.

Household Management
While lice do not survive long off the human body, simple cleaning steps can help prevent re-infestation. Clothing, bedding, and towels used by the infested person in the two days prior to treatment should be washed in hot water and dried on a high heat cycle. Items that cannot be washed may be sealed in a plastic bag for two weeks. Furniture and floors can be vacuumed to remove fallen hairs with attached nits.

When to See a Doctor
Most cases can be managed at home, but medical advice is recommended if:

• Over-the-counter treatments have failed after proper use
• There are signs of a secondary bacterial infection, such as redness, tenderness, crusting, or pus on the scalp
• The person infested is pregnant or breastfeeding
• The child is under two years old, as some medications are not approved for this age group
• There are open sores or broken skin on the scalp

Severity and Complications
Pediculosis capitis is generally considered a mild condition. It is not a vector for disease and does not cause serious systemic illness. However, severe infestations can lead to intense discomfort and sleep disruption. The most significant medical complication is a secondary bacterial infection, such as impetigo, caused by bacteria entering the skin through scratches. If left untreated, these skin infections can occasionally require antibiotic treatment.

Prognosis and Duration
The prognosis for head lice is excellent. With correct treatment, the infestation is typically eradicated. The duration depends on how quickly the condition is identified and treated. An active case can be cleared in a few weeks with appropriate medication and combing. However, recurrences are common if the treatment cycle is not finished (missing the second dose to kill hatched eggs) or if the person is re-exposed to an infested contact.

Factors Influencing Outcomes
Success depends largely on adherence to the treatment plan and checking household members. Using medication incorrectly—such as rinsing it out too soon or using too little—is a common reason for failure. Resistance to common insecticides is also a factor; in these cases, prescription treatments prescribed by a healthcare provider usually resolve the issue effectively.

Impact on Activities and Mental Health
While head lice are physically harmless, they can cause significant stress, anxiety, and embarrassment for children and parents due to social stigma. Children may feel isolated if they are kept home from school or activities, although medical organizations usually recommend against "no-nit" policies that exclude children from school solely for having nits. The process of treating and combing hair can be time-consuming and frustrating for families, impacting daily routines and causing friction between parents and children.

Coping Strategies
Managing the emotional side of head lice involves understanding that infestation is not a sign of poor hygiene. Keeping children occupied with a movie or book during the combing process can make the experience less stressful. Parents should focus on following instructions calmly without assigning blame.

Questions to Ask Your Healthcare Provider
Preparing questions can help ensure successful treatment. Consider asking:

• What is the best treatment option for my child's age?
• If the first treatment fails, how long should I wait before trying a different one?
• Do I need to treat other members of the household even if I don't see lice on them?
• How do I tell the difference between a live nit and an empty shell or dandruff?
• Is it safe to use home remedies like mayonnaise or olive oil?

Q: Can head lice jump or fly from person to person?
A: No. Head lice do not have wings and their legs are adapted for crawling and holding onto hair shafts, not jumping. They spread primarily through direct contact where hair touches hair.

Q: Does having head lice mean a person is dirty?
A: No. Head lice infestations are not related to personal hygiene or cleanliness in the home or school. Lice can thrive on anyone who has blood and hair, regardless of how often they bathe.

Q: Can I get head lice from my pets?
A: No. The head lice that affect humans are a specific species that only feeds on human blood. Dogs, cats, and other pets do not carry or transmit human lice.

Q: Do home remedies like mayonnaise or olive oil work?
A: While some people use occlusive agents like mayonnaise, olive oil, or butter to try to suffocate lice, scientific evidence for their effectiveness is mixed and generally weak. They may slow lice down, but they are often less effective than medicated treatments or diligent wet combing.

Q: How long do lice live on furniture or bedding?
A: Head lice need human blood to survive and typically die within 24 to 48 hours if they fall off a person. Nits (eggs) cannot hatch and usually die within a week if they are not kept warm near the scalp.