When people age, fluctuations in hormones related to the reproductive system cause _________.

As individuals age, there is a natural decline in hormone levels, particularly those associated with the reproductive system such as estrogen and testosterone. This hormonal fluctuation plays a significant role in skin health. One of the key effects of decreased hormone levels is the loss of collagen.

Collagen is a protein that provides structural support to the skin, contributing to its firmness and elasticity. As collagen production declines with age, the skin begins to lose its youthful appearance, leading to issues such as sagging, increased wrinkles, and overall loss of skin density. The decrease in collagen is a fundamental aspect of the aging process, directly affecting the skin's texture and elasticity.

In contrast, an increase in elastin typically does not occur with age; instead, elastin fibers can also degrade over time. Anemia is not directly related to hormonal changes affecting the skin, and dark circles are usually more often related to other factors such as genetics, fatigue, or health issues rather than hormonal fluctuations alone. Thus, the correct response reflects the significant impact that reduced hormones have on collagen levels in the skin during the aging process.