Laboratory Tests and Ancillaries
Wood’s light can help rule out other conditions of fungal etiology. Tinea capitis caused by Trichophyton tonsurans has a dry, white, diffuse scale that does not fluoresce under Wood’s light. Fungal culture and KOH examination are useful for atypical or resistant cases of scalp scaling.
Skin biopsies are not routinely done unless the diagnosis is uncertain. These may distinguish seborrheic dermatitis from similar disorders (eg psoriasis). The presence of epidermal parakeratosis, plugged follicular ostia, and spongiosis confirms seborrheic dermatitis. Dermatoscopy (dermoscopy, incident light microscopy) is another noninvasive technique used to identify morphologic features to differentiate seborrheic dermatitis from other scaling diseases.