This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
There is a defect in the production of melanin in all except- 
Select and explain. 
A. Albinism, B. Melasma, C. Vitiligo, D. Piebaldism
B: Melasma
Answer: B: Melasma 
Explanation: In melasma etiology is ultra violet rays. It is also triggered by pregnancy and oral contraceptive pills. All the other given conditions are associated with defects in melanin production.