What are pubic lice and where do they live?

What are Pubic Lice?

Appearance and Size

Pubic lice (Pthirus pubis), commonly called crabs, are tiny ectoparasites adapted to coarse body hair. Their bodies are flattened laterally, resembling miniature crab claws, which aid attachment to hair shafts. The thorax bears two prominent, chevron‑shaped, dark‑brown or tan plates that flank a central, lighter‑colored abdomen. Each adult carries three pairs of legs; the front pair is robust and equipped with claw‑like hooks for gripping hair, while the rear pairs are smaller and assist in locomotion.

Length: 1.0–2.0 mm (approximately the width of a grain of rice)
Width: 0.5–0.8 mm
Color: dark brown to tan, varying with blood engorgement
Body shape: dorsoventrally flattened, crab‑like silhouette

Nymphal stages resemble adults but are half the size and lack fully developed claws. Egg cases (nits) are oval, 0.5 mm long, and cemented to hair shafts near the base. The compact size and specialized morphology enable the insects to remain concealed within the pubic region, though they may also inhabit other coarse hair areas such as the axillae, chest, and facial hair.

Lifecycle of Pubic Lice

Pubic lice (Pthirus pubis) inhabit coarse body hair, most commonly the genital region, but may also colonize chest, abdominal, and facial hair. Their development proceeds through a fixed sequence of stages that occur entirely on the host.

The life cycle consists of three distinct phases:

Egg (nit): Female lice embed each egg cemented to a hair shaft near the skin. Eggs measure about 0.8 mm and hatch after 6–10 days, depending on temperature and humidity.
Nymph: Upon emergence, nymphs resemble miniature adults but lack fully developed genitalia. They undergo three molts, each lasting roughly 2–3 days, during which they increase in size and acquire reproductive capability.
Adult: Fully mature lice appear after about 9–14 days from the egg. Adults live on the host for 30–40 days, feeding on blood several times daily. Mating occurs shortly after the final molt; females lay 1–2 eggs per day for the remainder of their lifespan.

The entire cycle, from egg to reproducing adult, completes in approximately two weeks under optimal conditions. Continuous presence of lice on the host provides a stable environment for development, eliminating any need for a free‑living stage. Control measures must therefore target all three phases to interrupt reproduction and eradicate the infestation.

Where Do Pubic Lice Live?

Primary Infestation Sites

Pubic lice (Pthirus pubis) infest areas where coarse hair provides a secure grip for the insect’s claws. The primary sites include:

Pubic hair surrounding the external genitalia of both sexes
Perianal region and surrounding skin
Inner thighs where hair is present
Axillary (under‑arm) hair
Chest hair, particularly in men with dense growth
Facial hair such as beards, mustaches, and sideburns
Eyebrows and eyelashes, especially in children or individuals with extensive body hair

These locations share the characteristic of having thick, pigmented hair that supports the lice’s attachment and feeding behavior. Secondary spread may occur to any region with suitable hair, but the areas listed above constitute the most common concentrations during an initial infestation.

Less Common Locations

Pubic lice (Pthirus pubis) are small, wingless insects that feed on human blood. While they most frequently inhabit the coarse hair of the genital region, they can also establish colonies in areas where hair is present but infestation is uncommon.

Chest hair, especially in individuals with dense or long hair
Facial hair, including beards, moustaches, and sideburns
Armpit hair
Eyebrows and eyelashes; infestation may cause itching and irritation
Abdominal or back hair, particularly when body hair is extensive

These sites provide sufficient temperature and humidity for survival, but lower grooming frequency and reduced contact with contaminated clothing or bedding make them atypical. Detection requires careful visual inspection, and treatment follows the same protocol as for genital infestations.

Transmission and Spread

Pubic lice (Pthirus pubis) spread primarily through direct, sustained skin‑to‑skin contact. The most common route is sexual intercourse, where the insects transfer from one host’s pubic hair to another’s. Close, non‑sexual contact—such as sharing a bed or prolonged hugging—can also facilitate transfer when the lice have access to the hair shafts.

Additional vectors include personal items that retain live lice or viable eggs. Contaminated bedding, towels, underwear, and clothing may serve as temporary reservoirs, especially if they remain damp and are not laundered promptly. Viable eggs can survive up to 48 hours off the host, allowing indirect transmission under favorable conditions. Transmission via public surfaces—such as toilet seats, shower benches, or swimming pool decks—is extremely unlikely because lice require the warmth and humidity of the human body to remain active.

Key factors influencing spread:

Duration of contact: Transfer requires several minutes of continuous contact; brief encounters rarely result in infestation.
Environmental conditions: Warm, humid environments prolong lice survival on inanimate objects.
Hygiene practices: Regular laundering at temperatures above 60 °C eliminates both adult lice and eggs, reducing risk.
Population density: Crowded living situations increase the probability of shared items and close contact.

The incubation period ranges from 5 to 10 days, during which nymphs develop into mature lice capable of reproduction. An adult female can lay up to 30 eggs per day, depositing them near the base of hair shafts. High reproductive capacity accelerates spread within a community, particularly when untreated cases persist. Prompt diagnosis and treatment interrupt the life cycle, curtailing further transmission.

Symptoms of Pubic Lice Infestation

Common Signs

Pubic lice, also known as Pthirus pubis, are small, wingless insects that inhabit coarse body hair, primarily in the genital region but also in the armpits, chest, abdomen, facial hair, and occasionally eyebrows. Their presence produces a distinctive set of clinical signs that facilitate prompt identification.

Typical manifestations include:

Intense itching that intensifies after warm showers or prolonged periods of inactivity.
Visible mobile insects measuring 1–2 mm, often spotted on the hair shafts near the skin surface.
Small, bluish‑gray or tan eggs (nits) firmly attached to the base of hairs, usually arranged in a linear pattern.
Red or inflamed papules and tiny puncture wounds where lice have fed, sometimes developing into secondary bacterial infections.
Presence of brownish debris, the excrement of lice, which may appear as fine specks on clothing or bedding.

These indicators usually appear within a few days of infestation and persist until effective treatment eradicates the parasites. Early recognition of the signs enables timely intervention and reduces the risk of complications.

When to Seek Medical Attention

Pubic lice infest the hair of the genital area, perianal region, and occasionally coarse body hair. They feed on blood, causing irritation and a characteristic itching sensation. While over‑the‑counter treatments often eliminate the insects, certain circumstances demand prompt evaluation by a health professional.

Persistent itching or rash lasting more than two weeks despite treatment.
Visible signs of secondary bacterial infection, such as redness, swelling, pus, or warmth around the affected area.
Development of painful sores, ulcerations, or lesions that do not heal.
Presence of lice or eggs (nits) on atypical body sites, suggesting extensive spread.
Pregnancy, immunosuppression, or chronic skin conditions that could complicate standard therapy.
Uncertainty about diagnosis, especially when symptoms resemble other sexually transmitted infections.

Immediate medical consultation is advisable when any of these indicators appear. A clinician can confirm the diagnosis, prescribe prescription‑strength pediculicides, address complications, and provide counseling on prevention and partner treatment. Delaying care increases the risk of infection spread, prolonged discomfort, and potential secondary bacterial involvement.

Diagnosis and Treatment

How Pubic Lice are Diagnosed

Pubic lice (Pthirus pubis) are small, wingless insects that inhabit coarse body hair, most commonly the hair of the genital region, but also the hair of the abdomen, thighs, chest, armpits, beard, and eyelashes. Their presence is confirmed through specific diagnostic procedures.

Visual examination remains the primary method. A trained clinician inspects the affected area with a magnifying device, looking for live insects, nits (eggs) attached to hair shafts, and the characteristic brownish‑black fecal debris. Live lice are about 1–2 mm long and move slowly; nits appear as tiny, oval, translucent or brownish specks firmly cemented to the hair shaft near the scalp.

When visual clues are ambiguous, dermatoscopy (skin surface microscopy) provides enhanced magnification (×10–×30) and illumination, allowing clear differentiation between lice, nits, and other debris. Dermatoscopic images reveal the lice’s distinctive crab‑like shape and the anchoring of nits at a 45‑degree angle to the hair.

In laboratory settings, a sample of hair and attached material can be examined under a light microscope. The specimen is placed on a slide with a drop of saline or KOH solution, covered, and inspected at 40–100× magnification. Microscopic analysis confirms the species by identifying the lice’s short, broad body and the oval, operculated eggs.

Occasionally, a clinician may collect a few insects or nits for confirmation by a parasitology laboratory. The laboratory uses morphological keys to differentiate pubic lice from other ectoparasites such as head lice (Pediculus humanus capitis) or crab lice of animals.

Key points for accurate diagnosis:

Direct visual inspection with magnification
Dermatoscopic examination for enhanced detail
Microscopic analysis of hair samples
Laboratory identification when needed

Prompt recognition enables immediate treatment and prevents secondary transmission.

Over-the-Counter Treatments

Pubic lice, also known as crabs, are tiny parasitic insects that inhabit the coarse hair of the genital area, as well as the perianal region, chest, abdomen, and occasionally facial hair. They attach to hair shafts with claw‑like legs and feed on blood, causing itching and irritation.

Over‑the‑counter (OTC) products are the first line of treatment for a crab infestation. Most contain insecticidal agents that kill both adult lice and their nymphs. Effective OTC options include:

1% Permethrin cream – applied to the affected area for 10 minutes, then rinsed off. Requires a second application after 7 days to eliminate any newly hatched lice.
0.5% Malathion lotion – left on the skin for 8–12 hours before washing. Suitable for individuals with permethrin resistance; repeat treatment after 7 days.
Pyrethrin‑based shampoos – used similarly to permethrin, with a 10‑minute contact period. Often combined with piperonyl‑butoxide to enhance efficacy.
Dimethicone lotion – a silicone‑based product that suffocates lice. Applied for 30 minutes, then washed away. Minimal risk of skin irritation.

Application guidelines:

Wash the affected area with mild soap and warm water; dry thoroughly.
Apply the product according to package instructions, ensuring full coverage of hair shafts and surrounding skin.
Avoid sexual contact and sharing of clothing, towels, or bedding until treatment is complete and the environment is decontaminated.
Launder all fabrics in hot water (≥ 130 °F) and dry on high heat; items that cannot be washed should be sealed in a plastic bag for two weeks.
Perform a follow‑up inspection after 7 days; repeat treatment if live lice are observed.

Safety considerations:

Do not use OTC lice treatments on children under the age specified on the label.
Pregnant or nursing individuals should consult a healthcare professional before application.
Skin irritation, redness, or a mild burning sensation may occur; discontinue use and seek medical advice if symptoms persist.

When OTC products fail to eradicate the infestation after two complete cycles, prescription‑strength agents such as ivermectin or oral antihistamines may be required under medical supervision.

Prescription Medications

Pubic lice (Pthirus pubis) are obligate parasites that inhabit the coarse hair of the genital area, as well as axillary, facial, and chest hair. The insects attach their claws to hair shafts and feed on blood, causing itching and secondary skin irritation.

Prescription treatments target the lice and their eggs. The most frequently used agents include:

Permethrin 1 % cream – a synthetic pyrethroid applied to the affected area for ten minutes, then rinsed off; single application cures most infestations.
Ivermectin 200 µg/kg oral dose – a single tablet taken on an empty stomach; effective against both lice and nits, especially when topical therapy fails.
Malathion 0.5 % lotion – a phosphorothioate insecticide left on the skin for eight to twelve hours before washing; reserved for resistant cases.
Benzyl benzoate 25 % lotion – applied for 24 hours, then removed; useful for patients who cannot tolerate pyrethroids.

Each medication requires precise dosing and timing to ensure complete eradication. Contraindications include pregnancy (permethrin) and severe hepatic impairment (ivermectin). Common adverse effects are transient skin irritation, mild gastrointestinal upset, and, rarely, systemic toxicity. Resistance to pyrethroids has been documented; rotating agents or combining oral and topical therapy mitigates this risk.

After treatment, patients should repeat the application after seven days to eliminate newly hatched nits. Clothing, bedding, and towels must be washed in hot water or sealed in plastic for at least 72 hours to prevent re‑infestation. Follow‑up examination confirms clearance; persistent symptoms warrant a second course of a different prescription agent.

Preventing Reinfestation

Pubic lice, scientifically known as Pthirus pubis, inhabit the coarse hair of the genital area, perianal region, and occasionally chest or facial hair. After successful treatment, the risk of returning infestation remains high if preventive measures are not observed.

Effective strategies to avoid recurrence include:

Wash all clothing, bedding, and towels in hot water (minimum 130 °F) and dry on high heat for at least 30 minutes.
Store items that cannot be laundered in sealed plastic bags for two weeks, depriving parasites of a host.
Limit sexual contact with untreated partners; ensure they receive simultaneous therapy.
Conduct thorough inspection of hair and skin after exposure to potential sources; treat any detected nits promptly.
Maintain personal hygiene by showering daily and avoiding sharing personal items such as razors or underwear.

Consistent application of these actions eliminates residual eggs, reduces environmental contamination, and minimizes the probability of another outbreak.

Preventing Pubic Lice

Safe Practices

Pubic lice (Pthirus pubis) are tiny, wingless insects that feed on human blood. They inhabit the coarse hair of the genital region, but may also be found in the pubic‑area hair of the abdomen, thighs, armpits, chest, and facial hair such as beards. The insects cling to hair shafts with strong claws and lay eggs (nits) close to the skin surface.

Transmission occurs primarily through intimate skin‑to‑skin contact. Sharing contaminated clothing, towels, or bedding can also spread the parasites, although the risk from inanimate objects is lower because lice survive only a short time away from a host.

Safe practices:

Maintain personal hygiene; wash the genital area daily with mild soap.
Avoid sharing underwear, towels, or bedding; launder items at 60 °C or higher.
Use barrier methods (condoms, dental dams) during sexual activity to reduce direct contact.
Conduct regular visual inspections of pubic hair, especially after new partners.
Promptly apply an approved topical pediculicide (e.g., permethrin 1 % cream) when infestation is suspected.
Follow treatment instructions precisely; repeat application after 7–10 days to eliminate newly hatched lice.
Notify recent sexual partners so they can seek evaluation and treatment.
Dispose of used combs, brushes, and clothing in sealed bags until washed.

After treatment, re‑examine the area weekly for at least one month to confirm eradication. If symptoms persist, consult a healthcare professional for alternative therapy.

Cleaning and Disinfection

Pubic lice (Pthirus pubis) inhabit the coarse hair of the genital region, perianal area, and occasionally the eyebrows or chest. The insects cling to hair shafts and lay eggs (nits) close to the skin, where they are protected from most environmental conditions. Because the parasites survive only on a human host, eliminating them requires thorough removal of infested hair and disinfection of objects that may have contacted the lice.

Effective decontamination focuses on three categories: personal hygiene, laundering, and surface treatment.

Trim or shave affected hair to reduce habitat and facilitate nit removal.
Wash clothing, bedding, and towels in hot water (≥60 °C) and dry on high heat for at least 30 minutes.
Place non‑washable items (e.g., shoes, accessories) in sealed plastic bags for a minimum of two weeks to starve any remaining lice.
Apply an EPA‑registered disinfectant to surfaces such as upholstered furniture, bathroom fixtures, and shared grooming tools, following the manufacturer’s contact time.

Combining mechanical removal with proper laundering and chemical disinfection eradicates the parasite and prevents reinfestation. Regular inspection after treatment confirms success and reduces the risk of recurrence.