Which of the following is an example of an internal factor affecting skin health?

Hydration is indeed an example of an internal factor affecting skin health because it relates to the body's overall water content and how well the skin retains moisture internally. Adequate hydration is essential for maintaining skin elasticity, preventing dryness, and supporting the skin's barrier function. When the body is well-hydrated, it helps to ensure that skin cells can function optimally, leading to a healthier appearance.

In contrast, sun exposure is an external factor that can lead to skin damage, such as sunburn, premature aging, and increased risk of skin cancer. Cosmetic use primarily involves external products applied to the skin, which can have various effects depending on their ingredients. Pore size is also influenced by genetic and environmental factors but is not an internal factor in the same way that hydration and other bodily processes are. Therefore, hydration stands out as the internal factor in this context.