Which of the following is NOT a function of skin?

The correct answer highlights that skin does not synthesize vitamin A in the way suggested. While skin plays a role in synthesizing vitamin D when exposed to UV light, it is not involved in the direct synthesis of vitamin A. Vitamin A is primarily obtained through dietary sources, and the body metabolizes it for various functions, including vision and immune response.

In contrast, the other functions described are well-established roles of the skin. The regulation of body temperature through sweat is a critical function; the skin releases sweat, which cools the body as it evaporates. Additionally, the skin provides a protective barrier that shields internal organs from external elements, pathogens, and physical injuries. Furthermore, skin is involved in fat storage; adipose tissue within the skin not only serves as an energy reserve but also contributes to insulation and cushioning. These functions underscore the skin's vital role in maintaining overall bodily health and homeostasis.