Pediculosis pubis, commonly known as pubic lice or “crabs,” is an infestation caused by Phthirus pubis, a parasitic insect that feeds on human blood. These lice typically reside in the coarse hairs of the pubic region but may also be found in other areas with dense hair such as the armpits, chest, abdomen, and even eyelashes. While not as prevalent as head lice or body lice, pubic lice remain a significant concern due to their potential for sexual transmission and associated irritation.
Understanding Phthirus Pubis: The Cause of Pediculosis Pubis
Phthirus pubis is a wingless, blood-sucking ectoparasite adapted to grip coarse human hair with its claw-like appendages. Its body is broader than long, giving it a crab-like appearance — hence the nickname “crabs.”
Key Characteristics
- Size: 1–2 mm
- Shape: Broad and short with a crab-like structure
- Habitat: Pubic region, but may spread to thighs, chest, axillae, beard, and eyelashes
- Transmission: Primarily via sexual contact; occasionally via contaminated clothing, towels, or bedding
Lifecycle of Pubic Lice
The lifecycle of Phthirus pubis consists of three primary stages: egg (nit), nymph, and adult. The full cycle takes approximately 14–21 days.
Symptoms of Pediculosis Pubis: Recognizing the Infestation
The hallmark of pubic lice infestation is itching in the pubic area, usually becoming more intense at night. This itching is caused by an allergic reaction to louse saliva.
Common Clinical Signs
- Intense pruritus (itching) in the pubic region
- Erythematous papules and macules, especially around hair follicles
- Blue-gray discoloration (maculae ceruleae) from louse bites
- Lice and nits visible at the base of coarse hair
- Secondary bacterial infections due to scratching
- Dark, grainy fecal matter (louse excreta) visible on underwear
Sites Affected Beyond the Pubic Area
Though primarily localized, pubic lice may infest other areas of coarse hair:
- Axillary (armpit) hair
- Chest and abdominal hair
- Beard and mustache areas
- Eyelashes and eyebrows (especially in children)
Infestation of the eyelashes, known as phthiriasis palpebrarum, requires special clinical attention.
Modes of Transmission: How Pubic Lice Spread
Transmission occurs most frequently through sexual contact, making pediculosis pubis a sexually transmitted infestation (STI). Non-sexual transmission is rare but possible.
Common Transmission Routes
- Direct intimate contact with an infested person
- Sharing contaminated bedding, towels, or clothing
- Close nonsexual contact in households with infested individuals
Unlike head lice, pubic lice do not jump or fly. They crawl slowly and require direct or indirect physical contact for spread.
Diagnostic Approach to Pediculosis Pubis
Diagnosis is primarily clinical and based on visual identification of lice or eggs on coarse hair. In uncertain cases, additional tools may assist in confirmation.
Diagnostic Methods
- Visual examination under bright light or magnification
- Use of a fine-toothed louse comb to detect adult lice or nits
- Dermoscopy to differentiate lice from dandruff or debris
- Microscopy of removed lice or nits for confirmation
- Inspection of eyelashes in suspected pediatric cases
A thorough genital and body examination is recommended to identify multi-site infestations.
Treatment Protocols for Pubic Lice Infestation
Effective management of pediculosis pubis involves topical pediculicides, environmental decontamination, and treatment of sexual partners to prevent reinfestation.
First-Line Treatments
- Permethrin 1% cream rinse: Apply to affected areas, leave for 10 minutes, then rinse
- Pyrethrins with piperonyl butoxide: Safe and effective; apply for 10 minutes and rinse
- Malathion 0.5% lotion (off-label): Apply overnight, rinse in the morning
Alternative and Severe Cases
- Ivermectin (oral): Single 200 mcg/kg dose, repeated in 10 days if needed
- Petrolatum ointment for eyelashes: Applied 2–4 times daily for 10 days
- Manual removal of lice and nits from eyelashes using forceps or nit comb
Environmental Measures
- Wash clothes, bedding, and towels in hot water (≥130°F / 54°C)
- Dry items on high heat for at least 20 minutes
- Vacuum furniture and carpets
- Avoid sexual contact until treatment is complete and effective
Treating and Informing Sexual Contacts
To prevent reinfestation, all sexual partners within the past 30 days should be examined and treated if necessary. Partners must receive the same treatment regimen and be advised to abstain from sexual activity until both parties are lice-free.
Preventing Pediculosis Pubis: Proactive Measures
Although complete prevention is challenging due to the nature of transmission, certain steps can significantly reduce the risk.
Prevention Strategies
- Avoid sexual contact with infested individuals
- Do not share personal items like towels, underwear, or bedding
- Regular inspection after contact with new sexual partners
- Prompt treatment upon suspicion of infestation
- Safe sex practices and open communication with partners
Pubic lice infestation does not indicate poor hygiene, and personal cleanliness does not prevent infestation once contact is made.
Potential Complications
Untreated pediculosis pubis may lead to secondary complications:
- Skin infections from excessive scratching
- Eye irritation or conjunctivitis (if eyelashes are infested)
- Psychological stress or embarrassment
- Transmission of other STIs, given the shared risk factors
A comprehensive sexual health evaluation is often recommended to rule out coexisting sexually transmitted infections.
Differential Diagnosis: Conditions That Mimic Pediculosis Pubis
| Condition | Distinguishing Features |
|---|---|
| Folliculitis | Inflamed hair follicles, often with pus |
| Contact dermatitis | Rash with history of irritant or allergen |
| Scabies | Burrows, widespread pruritus including hands and feet |
| Tinea cruris | Ring-like fungal infection in groin |
| Dandruff or debris | Easily removed from hair shafts; not firmly attached like nits |
Special Considerations in Children
Detection of pubic lice in children may suggest non-sexual transmission from infested household members, particularly when localized to eyelashes or eyebrows. However, it should also prompt evaluation for possible sexual abuse, especially in cases of infestation in the genital area.
Pediculosis pubis is a common, treatable parasitic infestation predominantly transmitted through sexual contact. Prompt recognition, accurate diagnosis, and appropriate treatment are essential to eradicate the lice and prevent reinfestation. Public health measures, education on transmission, and partner management are crucial components of effective control strategies.
