What is the defining characteristic of UVA rays?

UVA rays have a defining characteristic of contributing to skin aging. Unlike UVB rays, which are primarily responsible for causing sunburn (the burning effect), UVA rays penetrate the skin more deeply and are associated with photoaging processes. This includes the breakdown of collagen and elastin, leading to wrinkles and loss of skin elasticity over time.

UVA rays are also known for their role in skin damage related to tanning and can stimulate melanin production, but their primary and most significant impact is their contribution to the visible signs of aging in the skin. Because these rays are present throughout the year and can penetrate windows, their damaging effects are not limited to direct sun exposure, thereby enhancing their role in skin aging regardless of the season or weather conditions.

In contrast, the other options refer to different aspects of UV radiation that are either specifically associated with UVB rays or represent effects that are not the defining characteristic of UVA rays.