Which of the following is considered an external factor affecting skin health?

Pollution is considered an external factor affecting skin health because it originates from the environment and can directly impact the skin's condition. Various pollutants, such as toxins, particulate matter, and chemicals in the air, can lead to skin issues like inflammation, irritation, premature aging, and increased susceptibility to breakouts. These external agents interact with the skin barrier, potentially causing oxidative stress and impairing the skin's natural functions.

In contrast, genetics is an intrinsic factor, as it relates to inherited characteristics that affect skin conditions and types. Hormones, also an intrinsic factor, influence skin health from within, often affecting oil production and other skin functions. Age is another intrinsic factor, as it encompasses the natural changes the skin undergoes over time due to biological processes rather than external influences. Thus, pollution stands out as the correct choice, being a variable that can change and affect the skin's health due to external environmental factors.