A Wood’s lamp is a small handheld device that uses black light to illuminate areas of your skin and allows the esthetician to analyze its health and specific needs. The presence of certain bacteria or changes in the pigmentation of your skin will cause the affected area to change color under the light. Normal healthy skin is slightly blue but shows white spots where there is thickened skin (needs extra exfoliation), yellow where it is oily, purple where it is dehydrated, and brown where there are areas of hyperpigmentation. Cutibacterium acnes, a bacterium involved in acne causation, exhibits an orange glow under a Wood's lamp.