What does a pubic louse look like on skin?

Understanding Pubic Lice: An Overview

The Basics of Pubic Lice

Pubic lice, also called Pthirus pubis, are tiny ectoparasites that inhabit the coarse hair of the genital area, perianal region, chest, abdomen, and occasionally facial hair. Adults measure 1–2 mm in length, have a crab‑like shape with a broad, flattened body, and display a dark brown to black coloration. Their legs are positioned laterally, giving the insect a rounded appearance that resembles a miniature crab.

Visible signs on the skin include:

Small, oval nits attached firmly to hair shafts about 0.8 mm from the scalp; nits appear white or pale yellow and do not detach easily.
Live insects that move slowly across hair shafts; they may be seen crawling when the host scratches or during close inspection.
Red or pink papules caused by bite reactions; these may be surrounded by a halo of inflammation.
Intense itching, typically worsening at night, resulting from the lice’s saliva injection.

The life cycle progresses from egg to nymph to adult within 2–3 weeks. Eggs hatch in 6–10 days; nymphs mature after an additional 9–12 days. Each female produces 8–10 eggs per day, leading to rapid infestation if untreated.

Transmission occurs primarily through direct sexual contact, but sharing infested clothing, towels, or bedding can also spread the parasites. Diagnosis relies on visual identification of live lice or nits during a thorough examination of affected hair zones.

Effective treatment options include:

Topical pediculicides containing 1 % permethrin or 0.5 % malathion, applied according to product instructions and repeated after 7 days to eliminate newly hatched nymphs.
Manual removal of nits with a fine-toothed comb after chemical treatment to reduce reinfestation risk.
Washing contaminated clothing, bedding, and towels in hot water (≥ 50 °C) and drying on high heat for at least 30 minutes.

Prevention focuses on avoiding intimate contact with infested individuals, using condoms or barrier methods when appropriate, and maintaining personal hygiene. Regular inspection after potential exposure helps detect early infestation and limits spread.

Size and Shape of Pubic Lice

Microscopic Appearance

Pubic lice (Pthirus pubis) are small, laterally compressed insects measuring 0.8–1.2 mm in length. Under magnification they appear as dark‑brown to black, crab‑shaped bodies with a broad, flattened thorax and a short, rounded head. The abdomen is broader than the thorax and bears six stout, clawed legs that grasp hair shafts.

Key microscopic characteristics:

Body segmentation: Distinct head, thorax, and abdomen; the head bears a compact set of mouthparts for blood feeding.
Leg morphology: Each leg ends in a pair of sharp claws; the front legs are larger, adapted for grasping coarse hair.
Eyes: Simple, lateral ocelli appear as tiny light‑reflective spots on the head.
Coloration: Uniformly pigmented, lacking the lighter abdominal bands seen in head lice.
Eggs (nits): Oval, 0.5 mm long, attached at a 45° angle to hair shafts; shells are translucent to whitish, becoming darker as embryos develop.

When examined on the skin surface, the louse’s flattened body conforms closely to the hair shaft, making the insect appear as a tiny, dark, crab‑like organism nestled among pubic hairs. The combination of size, shape, leg structure, and coloration distinguishes it from other ectoparasites.

Macroscopic Visibility

Pubic lice are visible to the naked eye as tiny, crab‑shaped insects measuring 1–2 mm in length. The body is flattened, with a broad, rounded head and six legs that cling to coarse hair. Color ranges from gray‑white to brown, often appearing translucent when the insect is alive and feeding. Movement is slow; lice crawl along the hair shaft and may be seen crawling over the skin surface near the base of the hair.

Visible signs on the skin include:

Small, dark specks that are the insects themselves, often clustered in the pubic region but also found in axillary or facial hair.
White or tan oval nits attached firmly to the hair shaft, positioned within 1 mm of the skin; they do not detach easily.
Red or pink irritation spots where a louse has bitten, sometimes accompanied by a small amount of blood or exudate.
Fine, grayish debris composed of dead lice and shed skins, forming a faint coating on hair shafts.

These macroscopic features allow identification without magnification, facilitating prompt diagnosis and treatment.

Coloration and Translucency

Pubic lice observed on the skin appear as tiny, flattened insects about 1–2 mm in length. Their overall hue ranges from light tan to brownish‑gray, depending on recent blood intake. After a recent meal, the abdomen may take on a reddish‑brown tint, while unfed specimens retain a paler, almost ivory coloration.

Light tan or ivory when unfed
Brownish‑gray in idle stages
Reddish‑brown abdomen after feeding

The cuticle of the louse is semi‑transparent, allowing internal structures to be seen through the body wall. Legs, antennae, and the ventral surface are discernible because the exoskeleton does not fully obscure them. This translucency makes the insect appear slightly glassy, especially when the abdomen is filled with blood, which creates a contrasting dark core visible through the thin outer layer.

Leg Structure and Claws

Pubic lice possess six legs, each ending in a pair of robust, hook‑shaped claws. The leg is divided into the coxa, trochanter, femur, tibia and tarsus; the tarsal segment terminates in the claws that latch onto individual hair shafts. These claws are curved, with a sharp point that penetrates the cuticle of the hair, allowing the insect to remain firmly attached while moving across the skin surface.

The claw arrangement enables the louse to grasp hairs at angles of 30‑45 degrees, creating a characteristic “jumping” motion when disturbed. On the skin, the insects appear as tiny, brownish oval bodies about 1–2 mm long, each anchored to a hair by the visible claw tips. The claws are often discernible as minute, dark extensions at the ends of the legs when the louse is examined under magnification.

Key features of the leg and claw system:

Six legs, each with a coxa‑trochanter‑femur‑tibia‑tarsus sequence.
Tarsal segment ends in a bifurcated, hook‑like claw.
Claws curve inward, forming a secure grip on hair shafts.
Adaptation allows rapid traversal of densely packed hair and resistance to removal.

These anatomical details explain why pubic lice cling tightly to body hair and why their presence is recognized by the combination of small, mobile insects and the characteristic nits attached to hair shafts.

Head and Mouthparts

Pubic lice are small, flattened insects measuring 1–2 mm in length. The head occupies the anterior third of the body and appears as a compact, rounded capsule with a slightly convex dorsal surface. The head’s coloration matches the surrounding exoskeleton, ranging from light brown to gray, allowing it to blend with the host’s skin and hair. Eyes are absent; instead, the head bears a pair of short, blunt antennae that rest close to the body and are rarely visible without magnification.

The feeding apparatus is located on the ventral side of the head and consists of several specialized structures:

Mandibles: two sharply pointed, serrated blades that pierce the epidermis to access blood vessels.
Maxillae: paired, broader plates that support the mandibles and assist in anchoring the louse to the skin.
Labrum: a thin, membranous cover that shields the mandibular tips when not in use.
Salivary glands: minute ducts opening near the mandibles, releasing anticoagulant fluid to facilitate blood intake.

These mouthparts are concealed beneath the head’s dorsal shield and become apparent only when the louse is actively feeding, creating a tiny, reddish puncture that may be observed on the skin surface.

Visualizing Pubic Lice on Skin

Appearance to the Naked Eye

Small Bumps or Specks

A pubic louse infestation commonly presents as minute elevations on the skin. These elevations are usually 1–2 mm in diameter, dome‑shaped, and may appear slightly raised or firm to the touch. Their color ranges from pinkish‑white to light brown, matching the surrounding epidermis, which can make them difficult to detect without close inspection.

In addition to bumps, the condition often produces tiny dark specks. These specks are the eggs (nits) cemented to the base of hair shafts. They measure about 0.5–0.8 mm, have a translucent gray‑brown hue, and may resemble small dandruff particles. When nits are viewed against light, they may appear as distinct, immobile dots.

Both manifestations tend to cluster in the pubic region, but can also be found on the thighs, abdomen, or any area with coarse hair. The combination of small, firm bumps and attached specks distinguishes a lice infestation from other dermatologic issues such as folliculitis, allergic dermatitis, or fungal infections.

Accurate identification requires magnification—handheld loupes or a dermatoscope—and careful separation of hair to expose nits. Absence of movement in the specks confirms they are eggs, while live lice may be observed crawling between the bumps.

Discoloration of the Skin

Pubic lice infestations frequently produce localized skin discoloration where the insects attach and feed. The affected area often appears as a small, reddish‑brown macule or patch, sometimes surrounded by a faint halo of erythema. The discoloration may be more pronounced in individuals with lighter skin tones, while darker skin may show a subtle, dusky hue.

Typical visual cues include:

Tiny, darkened spots at the base of each louse, corresponding to the insect’s exoskeleton after it detaches.
Minute, irregularly shaped plaques of hyperpigmentation that develop after repeated scratching.
Linear or clustered patterns of discoloration that follow the distribution of hair shafts in the pubic region.

These signs help differentiate lice‑induced changes from other dermatological conditions, such as fungal infections or allergic reactions, by their characteristic size, shape, and association with the presence of live or dead parasites.

Locations of Infestation

Hair-Bearing Areas

Pubic lice inhabit regions of the body where hair is dense, such as the genital area, the perianal region, the inner thighs, the chest, the abdomen, the armpits, and, in rare cases, facial hair. The insects are approximately 1–2 mm long, with a crab‑like body shape, a broad, flattened abdomen, and six legs equipped with clawed tarsi that cling tightly to hair shafts. Their coloration ranges from gray‑brown to dark brown, often blending with the host’s hair, which makes visual detection challenging without close inspection.

Key visual indicators in hair‑bearing zones include:

Live lice: small, mobile specks moving along hair shafts; they may be seen crawling or feeding at the base of the hair.
Nits (eggs): oval, translucent to white, firmly attached to the side of the hair about 1 mm from the scalp or skin surface; they cannot be removed by brushing alone.
Skin irritation: tiny red papules or tiny blood spots where the lice have bitten; these may appear as localized itching or a rash.

Because pubic lice grip hair rather than skin, they are most commonly found where hair is coarse and abundant. Examination of the affected area under magnification reveals the characteristic crab‑like morphology and the presence of nits cemented to each hair shaft. Accurate identification relies on observing these features directly on the hair‑bearing surface.

Less Common Sites

Pubic lice can infest areas beyond the typical genital region. On the torso, they attach to coarse hair of the abdomen, chest, and armpits. The insects appear as tiny, flattened, crab‑shaped bodies about 1–2 mm long, with a grayish‑brown hue. Nits are oval, white‑to‑yellow, and glued to the hair shaft close to the skin surface.

Other uncommon locations include facial hair (beard, moustache), eyebrows, and even scalp hair in individuals with dense, coarse hair. In these sites, lice retain the same morphology: a compact, six‑legged crustacean with a flattened back and visible claws grasping each hair. Nits remain firmly attached at the base of the hair, often forming a line of tiny, translucent beads.

Less frequent sites also encompass the inner thighs, perianal area, and the skin folds of the groin. In each case, observation reveals the characteristic crab‑like insect moving slowly across the hair, and the presence of nits that may be mistaken for dandruff but are firmer and more resistant to removal.

Skin Reactions to Infestation

Itching and Redness

Pubic lice infestation on the skin produces a distinctive pattern of irritation. The affected area typically exhibits persistent, localized itching that intensifies after prolonged contact or heat exposure. Scratching often leads to erythema, with redness ranging from mild pink to pronounced inflamed patches. Small, translucent or brownish spots may be visible where the insects feed, and the surrounding skin can appear slightly swollen.

Key clinical signs include:

Intense pruritus confined to the pubic region, sometimes extending to adjacent thighs or abdomen.
Redness that may be uniform or present as discrete, raised papules.
Visible lice or their eggs (nits) attached to coarse hair shafts, often appearing as tiny white or yellowish ovals.
Secondary lesions such as excoriations or crusted areas resulting from vigorous scratching.

Differentiation from other dermatological conditions relies on the presence of live insects or nits, the characteristic distribution of itch and redness, and the rapid onset of symptoms following exposure. Prompt identification enables targeted treatment and prevents further skin damage.

Bite Marks and Rashes

Pubic lice infestations frequently produce two distinct skin reactions: localized bite marks and broader rashes. The bite marks appear as tiny, red papules, often grouped in a line or cluster where the insect’s mandibles have pierced the epidermis. These lesions are typically 1–2 mm in diameter, may exhibit a central punctum, and are most common in the pubic region, but can also be seen on the abdomen, thighs, and perianal area.

The accompanying rash develops when the immune system reacts to lice saliva and shed exoskeletons. It manifests as a diffuse, erythematous area that may be slightly raised or papular. The rash can spread beyond the immediate site of attachment, sometimes forming a mottled pattern that follows the hair shaft distribution.

Key diagnostic features:

Size and shape: pinpoint to 2 mm papules, often linear.
Color: bright red to pink, sometimes with a peripheral halo.
Distribution: concentrated in coarse hair zones; may extend to adjacent skin.
Evolution: lesions appear within hours of attachment, persist for days, and may become crusted if scratched.

Recognition of these characteristics enables rapid identification of a pubic louse infestation and guides appropriate treatment.

Secondary Infections

Pubic lice appear as tiny, crab‑shaped insects clinging to coarse hair, often visible as moving gray‑brown specks. Their eggs (nits) are attached firmly to hair shafts, resembling tiny, white, oval shells that tilt toward the scalp. The infestation produces intense itching, redness, and small puncture marks where the insects feed.

Secondary bacterial infections frequently develop at sites of scratching or bite lesions. Common pathogens include Staphylococcus aureus and Streptococcus pyogenes, which cause:

Erythema and swelling around bite sites
Purulent discharge or crusted sores
Localized pain and warmth

Untreated infections may progress to cellulitis, characterized by diffuse skin thickening and spreading redness, or to impetigo, presenting as honey‑colored crusts. Prompt antimicrobial therapy, combined with effective lice eradication, reduces the risk of complications and promotes healing.

Distinguishing Pubic Lice from Other Conditions

Similarities to Scabies

Pubic lice and scabies share several visual and clinical characteristics that can cause diagnostic confusion. Both infestations produce small, moving lesions visible on the surface of the skin, and both may be accompanied by intense itching that worsens at night.

Size: Adult pubic lice measure 1–2 mm, comparable to the 0.3–0.4 mm scabies mite; their eggs (nits) are similarly tiny, appearing as white or grayish oval specks attached near hair shafts or skin folds.
Location of lesions: Lice are typically found in the pubic region, groin, and perianal area, while scabies burrows concentrate in the same warm, moist zones, as well as interdigital spaces and wrists.
Appearance of tracks: Lice leave visible excrement and blood spots that resemble the linear, gray‑white tracks (burrows) created by scabies mites as they tunnel beneath the epidermis.
Secondary signs: Both infestations may cause erythema, papules, and small vesicles resulting from scratching, leading to secondary bacterial infection if left untreated.

Distinguishing features include the presence of live insects in pubic lice cases, observable with a magnifying lens, whereas scabies is identified by the characteristic serpiginous burrow and the absence of motile organisms. Accurate examination of the affected area, combined with microscopic analysis of collected specimens, confirms the specific cause.

Differences from Other Parasites

Pubic lice (Pthirus pubis) are tiny, crab‑shaped insects about 1–2 mm long. Their bodies are broader than they are long, giving a rounded, flattened appearance. Color ranges from gray‑white to tan, often darkening after feeding. They cling tightly to coarse hair in the genital region, but may also inhabit chest, abdomen, armpits, or facial hair. Live insects move slowly, appearing as small, moving specks. Eggs (nits) are oval, 0.8 mm, firmly glued to hair shafts near the base and are opaque or slightly translucent.

Key distinctions from other human ectoparasites:

Head lice (Pediculus humanus capitis): longer, more slender body; prefer thin scalp hair; nits are attached higher on the shaft and can be removed more easily.
Body lice (Pediculus humanus corporis): live on clothing, not directly on hair; eggs are laid in seams of fabric; insects are larger and lack the crab‑like shape.
Fleas: jump actively, have hardened, laterally compressed bodies; move rapidly; bite without leaving visible nits on hair.
Ticks: significantly larger (several millimeters to centimeters); have a hard dorsal shield; attach firmly to skin for days, causing a distinct bite puncture rather than crawling over hair.
Scabies mite (Sarcoptes scabiei): microscopic (0.2–0.4 mm), burrow into skin, leaving serpiginous tracks; no visible insects or nits on hair shafts.

These morphological and behavioral traits allow clinicians to differentiate pubic lice from other parasites during visual examination.