 The superficial squamous cells have a clear, seemingly empty cytoplasm but it has not been shown that there is an increase in intracellular water, possibly making the term edema misleading.The histologic appearance is thought to be caused by water within the cells of the spinous layer causing the light to reflect back as whitish.The diagnosis is usually made based on the clinical appearance alone, but oral exfoliative cytology has been used as a diagnostic aid.