Symptoms of crabs (pubic lice)

Crabs or pubic lice may infect persons with good personal hygiene as well if they are in close body contact with an infected person.

The symptoms of pubic lice infestation are not apparent immediately. It may take a week to several weeks before the symptoms of the condition are apparent. The symptoms of pubic lice infestation are similar in both men and women.

It usually takes around 5 to 7 days to up to several weeks before the symptoms appear

There is a previous history of close bodily contact like sexual contact with an infected person. Use of condoms or other barrier methods do not prevent the spread of the lice as they live on hairs and can jump from person to person.

There may be a history of a nonsexual contact with an infected person as well. This could include kissing or hugging a person whose has lice infection in his beard or moustache.

Primary symptom of crabs

The primary symptom of crabs is severe itching. This often gets worse at night when the lice feed on human blood and are more active.

The itching is not caused by the bits but by an allergic or hypersensitivity reaction to the lice saliva that the skin is exposed to before the bite.

The itching is confined to the affected area – commonly the groin, but may also spread to the abdomen, thighs and legs. Those with infection of the other parts of the body like armpit hair, chest, abdomen or back hair, beard and moustache may also complain of itching in these areas.

Scratch marks and inflammation

Due to scratching the affected areas may be irritated and inflamed and red. There may be scratch marks.

Abraded skin due to scratching may also be broken and there may be secondary bacterial infections on the skin due to the lack of protective barriers of the skin in these areas.

Black powder on the underwear from crabs

There may be fine black powder on the underwear. This is faeces passed by the infecting lice.

infestation of Phthirus pubis

This patient presented with an infestation of Phthirus pubis, or crab lice. A Phthirus pubis infestation has caused the erythematous lesions seen in the pubic region of this patient in response to the bites of the crab lice arthropods. Image Credit: CDC/Joe Miller

Lice bites

The lice bites appear as sky blue spots over the skin of the groin, thighs, abdomen or other affected areas of the body. These usually fade in a day or so.

Tiny drops of blood or spots of blood may be visible over the affected skin and also stain the underwear.

Is it possible to see the lice?

The lice are around 1 to 2mm in size and are commonly yellowish grey or tan in color. They are difficult to see with the naked eye as they remain still when in light.

The eggs that the lice lay are firmly attached to the base of the hair over the affected areas. These are called nits. The eggs hatch in 6 to 10 days.

The empty greyish white shells of the eggs may be visible at the base of the hairs of the affected areas. They may look like dandruff, but unlike dandruff, they cannot be brushed away easily.

This however does not indicate an active lice infestation as these shells may persist for a while till the hair grows out or these fall off.

No symptoms

Some people may have no symptoms of pubic lice infestation. (1-6)

Further Reading

Last Updated: May 26, 2023

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


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