Which of the following best describes the mechanism of action for isotretinoin?

Isotretinoin primarily functions by reducing the size of sebaceous glands and subsequently decreasing sebum production. This action is crucial in treating severe acne, as excess sebum can contribute to clogged pores and the development of acne lesions. Isotretinoin acts on the sebaceous glands, shrinking their size and leading to a significant reduction in sebum output, which helps to prevent the formation of acne.

In contrast, while the other options may address aspects of skin health or acne treatment, they do not accurately reflect the specific mechanism by which isotretinoin operates. Option B, for instance, involves changes in blood flow that are not characteristic of isotretinoin’s primary action. C, referring to the repair of damaged skin cells, does not capture the drug's main action focused on oil production. D is related to anti-fungal activity, which is not relevant to the pharmacological profile of isotretinoin, as it is not an antifungal medication. Thus, the most accurate and descriptive choice regarding isotretinoin's mechanism of action is its ability to reduce sebaceous gland size and sebum production.