2.4.5 Pediculosis pubis

Grading & Level of Importance: B




Phthiriasis; infestation by crab lice; crabs.


Pruritic skin lesions in the pubic, perianal and axillary regions caused by bites from the pubic louse.

Aetiology & Pathogenesis

Pubic louse (Phthirus pubis): 1.3-1.6mm. Pubic lice live for only two days at room temperature without a host. Transmission by close personal contact, particularly sexual contact.

Signs & Symptoms

Pruritus in pubic or other hairy regions. Distinctive (but not common finding): slate grey to blue-grey macules as a result of haemosiderin degradation products at the bite site. Nits attached to hair shafts and adult lice are tightly attached to the hairs near the skin surface.


Hair bearing regions, especially pubic and perianal regions; can also affect the axillae, chest, abdomen, thighs and beard region. In children, eyelashes, eyebrows and rarely scalp can also be involved.


Not applicable.

Laboratory & other workups

The lice and nits can be identified by dermatoscopic examination.


Not necessary.


Persistence with inappropriate treatment. Re-infection with recurrences may occur.


Impetiginisation. Spreading to other people.


Clinical features. Identification of nits and lice.

Differential diagnosis

Prevention & Therapy

Prevention: Sexual contact should be avoided until both sexual partners have been successfully treated.

Therapy: General measures; similar management to pediculosis capitis. It is also important to treat sexual contacts. Topical treatment: malathion shampoo; permethrin cream rinse; synergized pyrethrin shampoo. Consider repeating treatment after 10 days. Oral ivermectin in resistant cases.


Examine the patient for other sexually transmitted diseases.

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