Cosmetics are defined as articles intended for which of the following purposes?

The definition of cosmetics is centered around their primary purpose, which is to enhance or alter the appearance of the human body. This includes products that are used for cleansing, beautifying, promoting attractiveness, or altering one's appearance without affecting the body's structure or functions in a medical way. Therefore, the focus on cleansing, beautifying, or altering appearance appropriately encompasses the typical uses of cosmetic products as recognized by regulatory standards.

Other options refer to functions that do not align with the primary intent behind cosmetics. For instance, enhancing nutritional value pertains more to food products rather than cosmetics, and preventing disease relates to pharmaceutical products or medical devices, which have a different regulatory framework and purpose. Lastly, acting as a pharmaceutical ingredient falls under the category of drugs, which are not defined as cosmetics. This clear distinction helps reinforce why the correct answer emphasizes appearance and beauty, aligning well with how cosmetics are classified by authorities like the FDA.