Light skin spots. Hypopigmentation or light skin spots, may be diagnosed easily in the office by a machine called a woods lamp. This is like a "black light". Causes of hypopigmentation are a decrease of melanin, melanocytes or the Amino Acid tyrosine. Sometimes a fungus of the skin may cause hypopigmentation so a simple culture of the skin can diagnose the cause. Complete loss of skin pigment is called vitiligo.
Observation. If there are areas of lighter pigmentation adjacent to or surrounded by normal pigmentation, the lighter areas are hypopigmented.