What is primarily responsible for skin aging?

Cumulative sun exposure is primarily responsible for skin aging due to its significant impact on the skin's structure and function over time. Ultraviolet (UV) radiation from the sun can damage collagen and elastin fibers in the skin, leading to loss of elasticity, wrinkles, and a rough texture. This type of damage is often referred to as photoaging, and it can result in pigmentation changes, such as age spots, as well as an increased risk of skin cancers.

While genetic factors also contribute to how skin ages, they do not have as immediate or pronounced an effect as sun exposure. Regular exercise can improve blood circulation and overall health but does not directly prevent the aging effects of environmental factors like UV radiation. Increased moisture retention is generally beneficial for maintaining skin's hydration and appearance but does not address the underlying issues caused by exposure to the sun's harmful rays. Thus, the long-term effects of cumulative sun exposure are the most significant contributors to the visible signs of aging in the skin.