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
[{'content': 'Patch testing is done for – \nSelect and explain. \nA. Atopic dermatitis, B. Irritant contact dermatitis, C. Allergic contact dermatitis, D. Discoid dermatitis', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Patch test is the only effective means of confirming contact dermatitis.\nNow the question arises for which type of contact dermatitis (Irritant or allergic) the test is done.\nYou know that allergic contact dermatitis is type IV hypersensitivity against particular antigen, where as irritant contact dermatitis is due to irritant action of the chemical.\nIn patch test reading is taken after 48-72 hours to see the signs of delayed hypersensitivity, i.e. induration.\nSo, patch test relies on the principal of type IV (delayed type) hypersensitivity and type IV hypersensitivity is the pathogenic mechanism in allergic contact dermatitis.', 'role': 'assistant'}]