Module 1.4 Macule, Erythema and Excoriations
PEDICULOSIS CAPITIS (HEAD LICE)
Fitzpatrick’s Dermatology in General Medicine [9E]
AT-A-GLANCE ● Infestation occurs worldwide affecting hairs of the scalp most commonly in children between the ages of 3
and 12 years.
● Presence of 0.8-mm eggs (nits) firmly attached to scalp hairs is most common sign of infestation.
● Spread by close physical contact and sharing of headgear, combs, brushes, and pillows.
● Resistance to traditional nonprescription preparations is growing; topical malathion and ivermectin should
be considered in resistant cases.
EPIDEMIOLOGY Prevalence:
● Head lice infestations are common worldwide, particularly in children aged 3 to 12 years.
● In the U.S., an estimated 10 to 12 million children are infested each year, based on pediculicide sales.
Demographics:
● Head lice infestations affect all societal levels and ethnic groups.
● The incidence is lower among African Americans, possibly due to the inability of female lice to deposit eggs
on coarse, curly hair.
Trends:
● A study by Koch and colleagues observed an increase in prescriptions for lice treatment, suggesting either
an increase in infestation rates or higher failure rates of over-the-counter treatments.
Transmission:
● Primary mode: Direct head-to-head contact.
● Less common mode: Indirect transmission through fomites, such as:
○ Combs, brushes, blow-dryers
○ Hair accessories
○ Upholstery, pillows, bedding
○ Helmets, other headgear
● Lice can be dislodged by air movement, blow-dryers, combs, and towels, which can lead to passive
transfer to fabrics and potentially result in new infestations.
ETIOLOGY AND PATHOGENESIS Organism Characteristics:
● Head lice are blood-sucking, wingless insects from the order Anoplura.
● They are highly host-specific and approximately 2 mm long.
● They have 3 pairs of claw-like legs adapted to grasp human hair.
● The entire life cycle of head lice occurs on the scalp.
Infestation Details:
● More than 95% of infested individuals have fewer than 100 adult lice on their scalp.
● Female lice lay 5 to 10 eggs per day during their 30-day life span.
● The eggs hatch after 10 days, producing nymphs or instars (miniature adult lice).
● Instars go through 3 developmental stages, taking 14 days to reach full maturity.
Egg (Nit) Characteristics:
● Eggs are laid approximately 1 cm from the scalp, attached firmly to individual hairs by a proteinaceous
, glue secreted by female lice.
● This glue has an amino acid composition similar to human hair.
Survival Away from Host:
● Lice can survive less than 2 days away from the scalp but may survive up to 4 days in favorable
conditions of heat and humidity.
● Nits (eggs) can survive up to 10 days away from the scalp.
CLINICAL FINDINGS Location of Infestation:
● Pediculosis capitis (head lice) is confined to the scalp.
● Nits are most commonly found in the occipital and retroauricular (behind the ears) regions.
Common Symptoms:
● Pruritus (itching) is the most common symptom.
● The incubation period before symptoms appear is 4 to 6 weeks.
● Some individuals may remain asymptomatic, serving as carriers.
Skin Findings:
● Mite bites may result in 2-mm erythematous macules or papules.
● However, common findings include excoriations (scratches), erythema (redness), and scaling.
● Other possible symptoms include low-grade fever, regional lymphadenopathy (swollen lymph nodes),
and irritability.
DIAGNOSIS/DIFFERENTIAL DIAGNOSIS Diagnosis:
● Diagnosis is based on finding egg capsules (nits) and live lice.
● Nits are easily seen with the naked eye and indicate past or present infestation.
● Nits can be distinguished from dandruff or hair casts, as they are firmly attached to the hair shaft and
cannot be easily removed.
● The color of viable nits is tan to brown, while hatched nits are clear, white, or light in color.
● Newly laid eggs are usually found close to the scalp, while hatched nits are further away.
● Dermoscopy can reveal lice embryos in unhatched eggs.
Identification of Lice:
● Presence of adult lice confirms active infestation.
● Lice are difficult to find as they are fast, avoid light, and blend in with the hair.
● Fine combing with a nit comb is the best way to find live lice or immature nymphs.
● Wet combing (using water and conditioner) improves the detection of lice by loosening them from the hair
follicles.
PEDICULOSIS CAPITIS (HEAD LICE)
Fitzpatrick’s Dermatology in General Medicine [9E]
AT-A-GLANCE ● Infestation occurs worldwide affecting hairs of the scalp most commonly in children between the ages of 3
and 12 years.
● Presence of 0.8-mm eggs (nits) firmly attached to scalp hairs is most common sign of infestation.
● Spread by close physical contact and sharing of headgear, combs, brushes, and pillows.
● Resistance to traditional nonprescription preparations is growing; topical malathion and ivermectin should
be considered in resistant cases.
EPIDEMIOLOGY Prevalence:
● Head lice infestations are common worldwide, particularly in children aged 3 to 12 years.
● In the U.S., an estimated 10 to 12 million children are infested each year, based on pediculicide sales.
Demographics:
● Head lice infestations affect all societal levels and ethnic groups.
● The incidence is lower among African Americans, possibly due to the inability of female lice to deposit eggs
on coarse, curly hair.
Trends:
● A study by Koch and colleagues observed an increase in prescriptions for lice treatment, suggesting either
an increase in infestation rates or higher failure rates of over-the-counter treatments.
Transmission:
● Primary mode: Direct head-to-head contact.
● Less common mode: Indirect transmission through fomites, such as:
○ Combs, brushes, blow-dryers
○ Hair accessories
○ Upholstery, pillows, bedding
○ Helmets, other headgear
● Lice can be dislodged by air movement, blow-dryers, combs, and towels, which can lead to passive
transfer to fabrics and potentially result in new infestations.
ETIOLOGY AND PATHOGENESIS Organism Characteristics:
● Head lice are blood-sucking, wingless insects from the order Anoplura.
● They are highly host-specific and approximately 2 mm long.
● They have 3 pairs of claw-like legs adapted to grasp human hair.
● The entire life cycle of head lice occurs on the scalp.
Infestation Details:
● More than 95% of infested individuals have fewer than 100 adult lice on their scalp.
● Female lice lay 5 to 10 eggs per day during their 30-day life span.
● The eggs hatch after 10 days, producing nymphs or instars (miniature adult lice).
● Instars go through 3 developmental stages, taking 14 days to reach full maturity.
Egg (Nit) Characteristics:
● Eggs are laid approximately 1 cm from the scalp, attached firmly to individual hairs by a proteinaceous
, glue secreted by female lice.
● This glue has an amino acid composition similar to human hair.
Survival Away from Host:
● Lice can survive less than 2 days away from the scalp but may survive up to 4 days in favorable
conditions of heat and humidity.
● Nits (eggs) can survive up to 10 days away from the scalp.
CLINICAL FINDINGS Location of Infestation:
● Pediculosis capitis (head lice) is confined to the scalp.
● Nits are most commonly found in the occipital and retroauricular (behind the ears) regions.
Common Symptoms:
● Pruritus (itching) is the most common symptom.
● The incubation period before symptoms appear is 4 to 6 weeks.
● Some individuals may remain asymptomatic, serving as carriers.
Skin Findings:
● Mite bites may result in 2-mm erythematous macules or papules.
● However, common findings include excoriations (scratches), erythema (redness), and scaling.
● Other possible symptoms include low-grade fever, regional lymphadenopathy (swollen lymph nodes),
and irritability.
DIAGNOSIS/DIFFERENTIAL DIAGNOSIS Diagnosis:
● Diagnosis is based on finding egg capsules (nits) and live lice.
● Nits are easily seen with the naked eye and indicate past or present infestation.
● Nits can be distinguished from dandruff or hair casts, as they are firmly attached to the hair shaft and
cannot be easily removed.
● The color of viable nits is tan to brown, while hatched nits are clear, white, or light in color.
● Newly laid eggs are usually found close to the scalp, while hatched nits are further away.
● Dermoscopy can reveal lice embryos in unhatched eggs.
Identification of Lice:
● Presence of adult lice confirms active infestation.
● Lice are difficult to find as they are fast, avoid light, and blend in with the hair.
● Fine combing with a nit comb is the best way to find live lice or immature nymphs.
● Wet combing (using water and conditioner) improves the detection of lice by loosening them from the hair
follicles.
