What is known to cause age spots or hyperpigmentation on the backs of the hands?

The correct response is based on the understanding of how different types of light affect the skin. UVA light is primarily responsible for causing skin damage that can lead to hyperpigmentation, also known as age spots. It penetrates deeply into the skin and can cause long-term effects, including the breakdown of collagen and the uneven production of melanin, both of which contribute to the formation of age spots, especially in areas frequently exposed to sunlight, like the backs of the hands.

While UVB light is also associated with skin damage, it primarily affects the outer layers of skin and is more associated with sunburn. Infrared light doesn't significantly cause hyperpigmentation; it is more associated with heat rather than direct damage to the skin's pigment-producing cells. X-ray exposure can have other health implications, but it does not typically lead to the age spots that are specifically associated with prolonged sun exposure and UVA rays. Thus, understanding the role of UVA light in skin aging and pigmentation issues makes it the correct choice for this question.