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What Are Pubic Lice?
Pubic lice, colloquially known as “crabs” due to their crab-like flattened appearance, are parasitic insects that infest the hair of the pubic region. They are visible to the naked eye as tiny, six-legged, crawling creatures that attach to pubic hair and lay eggs (called nits).
Although pubic lice most commonly infest the pubic area, they can also establish themselves in:
- Armpit hair
- Chest and abdominal hair
- Eyelashes and eyebrows (particularly in young children)
Pubic lice infestation is a common, often embarrassing, but typically not dangerous condition. The prognosis is excellent, particularly when the infestation is detected and treated early while the number of parasites is still small.
Key Transmission and Symptoms Overview
- Transmission: Primarily through sexual contact
- Main symptoms:
- Intense intimate itching, characteristically worse at night
- Visible reddish-purple spots (bite marks)
- Skin abrasions and potential secondary infections from scratching
How Long Does the Infestation Last?
A single course of treatment is usually sufficient to eliminate the adult parasites. However, a second application must be repeated 7–10 days later to ensure the destruction of any eggs (nits) that may have been viable at the time of the first treatment but have since hatched into newly active lice.
Without treatment, the infestation will not resolve spontaneously; it will persist and potentially worsen.
How Are They Transmitted?
Pubic lice infestation is primarily a sexually transmitted infection (STI). It spreads through close physical contact during sexual activity, specifically skin-to-skin or hair-to-hair contact in the genital region.
Less common routes of transmission:
- Fomites (indirect contact with contaminated objects): Shared bedding, towels, or clothing, though this route is significantly less efficient than direct contact, as lice cannot survive away from a human host for more than 48–72 hours.
- Anecdotal reports of transmission via sharing or trying on clothing exist, but robust evidence is lacking.
Note: Pubic lice cannot be transmitted by or to animals; pets (dogs, cats, etc.) do not carry Phthirus pubis and cannot be a source of infestation.
In addition to pubic lice (Phthirus pubis), two other species of lice infest humans:
- Head lice (Pediculus humanus capitis) infest the scalp
- Body lice (Pediculus humanus corporis) infest clothing and body seams
Risk Factors
The following factors significantly increase the likelihood of acquiring pubic lice:
- Being a sexually active adolescent or young adult
- Having multiple sexual partners
- Having unprotected sexual contact with an infected person
- Sharing a bed or clothing with an infected person
Where Do They Come From?
Pubic lice cannot appear spontaneously. When an infestation is diagnosed, whether it involves pubic or head lice, it invariably means that contact with an infected source has occurred: either through another person (most commonly) or, less frequently, through a contaminated object.
There is no scientific basis for the notion that lice “generate spontaneously” from uncleanliness or poor hygiene. Pubic lice are an indiscriminate parasite; they can affect people of any socioeconomic background.
Symptoms
The main symptoms associated with pubic lice infestation include:
Itching
- Intense itching in the pubic, genital, and perianal areas; this is the most common and often the first symptom
- The itching typically worsens at night, when the lice are most active and feeding
- Severity can range from mild discomfort to severe, sleep-disrupting pruritus
Why does the itching occur? Pubic lice feed exclusively on human blood. When feeding, they insert their mouthparts into a hair follicle and inject saliva containing anticoagulant substances, which triggers an immune-mediated inflammatory and pruritic (itching) reaction in the skin.
Visible Parasites and Nits
- Adult lice: visible to the naked eye as tiny (1–2 mm), grayish-white or brownish, crab-shaped creatures that are firmly anchored at the base of pubic hairs
- Nits (eggs): tiny white or yellowish-white oval structures cemented firmly to the hair shaft. Unlike dandruff, they do not slide off the hair easily
Skin Changes
- Reddish-blue or grayish-blue spots (maculae caeruleae or “sky-blue macules”): small, slate-colored skin stains caused by the louse’s feeding activity. These are characteristic but not always present.
- Skin abrasions and excoriations from repeated scratching.
- Secondary bacterial skin infections from breaks in the skin caused by scratching.
Onset: Symptoms may appear shortly after infestation or take up to a month to develop, particularly in a person with no prior exposure whose immune system has not yet mounted a response to the louse saliva.
Possible Complications
In otherwise healthy individuals, pubic lice infestation is a manageable condition with an excellent prognosis. The primary complication risk is:
- Secondary bacterial skin infections from skin damage caused by scratching (excoriations can become secondarily infected with bacteria)
- In infants and young children with eyelash infestation: blepharitis (eyelid infection), which requires prompt specialist evaluation
When to See a Doctor
Consult your doctor if:
- You or your sexual partner develop symptoms suggestive of pubic lice infestation
- Over-the-counter treatments have been used but proved ineffective
- The infestation involves the eyelashes or eyebrows
- Signs of secondary bacterial infection are present (increasing redness, warmth, pus, or crusting)
The specialist responsible for the diagnosis and management of pubic lice is the dermatologist-venereologist.
Diagnosis
The diagnosis of pubic lice infestation is primarily clinical, based on the visual identification of adult parasites or nits.
Physical Examination
The physician performs a careful inspection of:
- The pubic region and surrounding genital area
- Axillary hair (armpit)
- Abdominal and chest hair
- Eyelashes and eyebrows (particularly in children)
What to look for:
- Adult lice: Small (1–2 mm), grayish-white or brownish, crab-shaped insects, often firmly grasping a hair shaft at the base. They may appear motionless but move when disturbed
- Nits (eggs): Tiny white-yellowish ovals, firmly cemented to the hair shaft (unlike dandruff, they do not brush off easily)
- Skin changes: Excoriations, maculae caeruleae, or signs of secondary infection
Dermatoscopy and Microscopy
Dermatoscopy (dermoscopy) is now considered the standard tool for immediate, painless confirmation of pubic lice infestation:
- A handheld or digital dermatoscope provides high-magnification visualization of the parasite, allowing the physician to observe the louse’s movements and the viability of the nits
- Distinguishes Phthirus pubis from other parasites and skin conditions
In doubtful cases, a hair sample can be examined under a light microscope to definitively identify the species.
Screening for Sexually Transmitted Infections
Because pubic lice are sexually transmitted, their diagnosis should always trigger a broader STI screening protocol. Current clinical guidelines strongly recommend testing for:
Signs of secondary skin infections, such as impetigo, may be present and should be addressed during the evaluation.
Treatment
The goal of therapy is the complete elimination of both adult parasites and viable eggs (nits) to prevent recurrence and further transmission. Treatment combines pharmacological agents, hygienic environmental measures, and management of sexual contacts.
First-Line Pharmacological Therapies
Topical treatments are the first choice and are available in pharmacies as gels, shampoos, or emulsions. The most commonly used active agents include:
Permethrin (1%)
- The gold standard treatment, preferred for its excellent efficacy and safety profile
- Application: Apply to the affected hairy areas and rinse off after approximately 10 minutes
- Safe for use in adults, children over 2 months, and pregnant women (under medical guidance)
Pyrethrins with Piperonyl Butoxide
- Natural compounds derived from chrysanthemums, synergistically enhanced by piperonyl butoxide
- Effective against live adult lice
- Available as shampoos and rinses
Malathion (0.5%)
- Used in selected cases or when resistance to other agents is suspected
- Has ovicidal activity (kills eggs as well as adults), which is an advantage over some other agents
- Should be applied and allowed to dry naturally (without a hairdryer) before washing off
Critical: The product must be applied not only to the pubic area but to all hairy areas from the waist to the knees, including the inner thighs, perianal region, and axillary hair, to ensure complete eradication.
Application Protocol and Resistance Management
A single treatment is often insufficient to eliminate all viable eggs. The recommended protocol is:
- First application: On day 1
- Second application: Repeated 7–10 days later to kill any lice that have hatched from eggs since the first treatment, as topical agents typically have limited ovicidal activity
When oral therapy is needed: In cases of massive infestation or resistance to topical treatments, the physician may prescribe:
- Ivermectin (oral): A systemic antiparasitic agent; typically administered as two oral doses separated by 7–14 days. While not a first-line treatment, it has demonstrated very high efficacy in difficult or treatment-resistant cases.
Management of Eyelash Infestation
When lice infest the eyelashes or eyebrows, standard pubic lice treatments must not be used; they are irritating and potentially dangerous to the eyes and vision.
Alternative approaches under medical supervision include:
- Manual removal of lice and nits using fine-tipped tweezers
- Application of ophthalmic petrolatum (vaseline) to the eyelashes creates a suffocating environment for the lice without chemical irritation. It should be applied 2–4 times daily for approximately 10 days
- Specialist ophthalmological assessment is recommended in all cases of eyelash infestation
Lifestyle and Environmental Decontamination
The success of pharmacological treatment is critically dependent on concurrent environmental and behavioral measures:
Treat all sexual partners simultaneously:
- All sexual partners from the preceding 30 days must be evaluated and treated concurrently, even if they are asymptomatic. Failure to do so leads to immediate re-infestation (the “ping-pong” effect).
Laundry decontamination:
- Wash all bedding, towels, and clothing used in the 2–3 days before treatment in a washing machine at 60°C (140°F). Heat kills both lice and nits.
The “bag method” for non-washable items:
- Items that cannot be machine-washed at high temperature (stuffed animals, pillows with delicate covers, etc.) should be sealed in an airtight plastic bag for at least 2 weeks
- Without access to a human host, pubic lice die within 48–72 hours
Sexual abstinence:
- Avoid all sexual contact until both you and your partner(s) have completed the full treatment course and are confirmed clear of infestation
Environmental insecticide sprays:
- NOT necessary or recommended: there is no evidence that professional fumigation or household insecticide sprays provide additional benefit
Shaving:
- Shaving the pubic hair may facilitate application of topical treatments and physical removal of nits, but is not essential for treatment success if pharmacological therapy is applied correctly
Prevention
The only truly effective prevention strategy is avoiding close physical or sexual contact with an infected individual.
Important Limitation of Condoms
It is critical to note that condoms do not protect against pubic lice. Unlike STIs transmitted through genital secretions, pubic lice spread through direct hair-to-hair or skin-to-skin contact in areas not covered by a condom, most notably the inner thighs, mons pubis, and perianal regions.
General Preventive Measures
- Reducing the number of sexual partners reduces exposure risk
- Avoiding sharing of bedding, towels, and clothing with potentially infected individuals
- Early diagnosis and treatment at the first signs of symptoms limits both personal suffering and the risk of onward transmission
- Informing recent sexual partners about the infestation so they can be tested and treated promptly
STI Awareness
Because pubic lice infestation signals unprotected sexual contact, it represents an important opportunity for sexual health counseling, including:
- Discussion of safer sex practices
- Offer of comprehensive STI screening
- Review of contraception options
Sources and Bibliography
- British Association for Sexual Health and HIV (BASHH). UK National Guideline for the Management of Phthirus pubis Infestation. 2016.
- Workowski KA, Bachmann LH, et al. “Sexually Transmitted Infections Treatment Guidelines, 2021”. MMWR Recommendations and Reports. 2021;70(4):1–187. CDC.
- CDC: Pubic Lice (Crabs)
- Nair BK. “Phthiriasis palpebrarum”. Indian Journal of Ophthalmology. 2013;61(8):465–466.
- NHS: Pubic Lice
- DermNet NZ: Pubic Lice
- Mayo Clinic: Pubic Lice
