Pediculosis (Lice)

Initial Evaluation

The lice, eggs, or nits (empty egg casings) are not always obviously visualized. Important clues include excoriated erythematous papules (shown in this image) or maculae ceruleans (slate-blue macules) on areas of skin that come in contact with the hair.

The eggs of head lice are highly monomorphous ovoid structures that are firmly attached to the hair shaft via a white concretion such that they are challenging to remove. These are typically located close to the scalp (within millimeters) and may camouflage into the hair. The incubation time of head louse eggs ranges from 7-12 days, depending on heat exposure and weather. When empty, these egg casings are referred to as nits and are typically lighter in color and easier to visualize. Important diagnostic considerations are hair shaft casts (circumferential keratinous bands that easily slide up and down the hair shaft), seborrheic dermatitis (loose, greasy scale that is very loosely adherent to hair, if at all), and a superficial fungal infection of the hair shaft. It is important to note that the primary mode of transmission of hair lice is through direct contact with the head of an affected individual, though rarely may also occur through fomites such as hats and hair brushes.

Head louse

[Reproduced with the permission of the University of Nebraska-Lincoln Extension. Managing head lice safely (018). UNL Extension-Lancaster County. Accessed November 2, 2012.]

Pubic lice may also affect the eyelashes

[Pubic lice on eyelashes. Accessed November 2, 2012.]

Differential diagnosis


Tick bite

Bullous arthropod

Papular urticaria