This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Other topics and Adverse effects, Subject name: Pharmacology
Psoralen-A is used in the treatment of: 
Select and explain. 
A. Pemphigus, B. Vitiligo, C. Pityriasis alba, D. Icthyosis
B: Vitiligo
Answer: B: Vitiligo 
Explanation: Photochemotherapy (PUVA: Psoralen ultraviolet A)- Photoactivated psoralen undergoes 02 independent as well as 02 dependent reactions and binds to pyrimidine bases- interferes with DNA synthesis and epithelial cell turnover. Oral methoxsalen is followed 1-2 hours later by UVA exposure on alternate days. ESSENTIALS of medical PHARMACOLOGY SEVENTH EDITION-KD TRIPATHI page:892