How to distinguish lice from allergy?

Question

admin · Accepted Answer

How to distinguish lice from allergy? - briefly
Examine the scalp: live lice or nits attached to hair shafts confirm infestation, while allergic dermatitis presents as diffuse redness, swelling, and a rash without any eggs on the hair. Microscopic inspection or a fine‑toothed comb can verify parasites, whereas a contact‑allergy reaction remains egg‑free.

How to distinguish lice from allergy? - in detail
Head lice infestations and allergic skin reactions produce similar discomfort, yet they can be separated by examining specific signs.

Location of irritation

Lice bite the scalp and neck; itching is most intense at the hairline, behind the ears, and the nape.
Allergic dermatitis often appears on the forehead, temples, or areas that have contacted a trigger (e.g., shampoo, hair dye).

Visual evidence

Live insects are visible as gray‑brown, wingless bodies about the size of a sesame seed moving among hairs.
Nits (lice eggs) are oval, firmly attached to the hair shaft within ¼ inch of the scalp; they appear white or yellowish and do not detach easily.
Allergic lesions manifest as red papules, vesicles, or dry scaling without moving organisms or attached eggs.

Pattern of spread

Lice spread rapidly among close contacts; multiple family members or classmates usually show symptoms within days.
An allergic response typically remains limited to the individual unless the irritant is shared.

Timing of symptoms

Itching from lice intensifies several hours after feeding and may worsen at night.
Allergy‑related itch often begins shortly after exposure to the offending substance and may improve with avoidance.

Response to treatment

Application of a pediculicide (e.g., permethrin) eliminates live lice and nits; symptoms diminish within a few days.
Topical corticosteroids or antihistamines reduce allergic inflammation; they have no effect on lice.

Diagnostic aid

Use a fine‑tooth comb on wet hair, section by section, to capture any moving insects or nits.
Perform a patch test with suspected allergens to confirm hypersensitivity.

By systematically assessing these factors—visual inspection for insects and eggs, distribution of rash, symptom onset, and reaction to appropriate therapy—clinicians can reliably differentiate a lice infestation from an allergic skin condition.