Final answer:
Increased skin damage and infection in the elderly is mainly caused by decreased sensitivity of the immune system, which results from age-related immune decline known as immunosenescence. While other factors may affect skin health, they are not as directly linked to increased skin damage and infections as the immune system's decreased effectiveness.
Step-by-step explanation:
A factor which causes increased skin damage and infection in the elderly is decreased sensitivity of the immune system. In the aging process, especially when considering the integumentary system, a notable change is the decrease in cell division and metabolic activity, resulting in changes like a thinner epidermis and a less resilient dermis. Furthermore, the immune system becomes less effective due to a process called immunosenescence, making it more difficult for elderly individuals to fend off diseases and infections, and as such, it makes the skin more vulnerable to damage and subsequent infections.
Although other factors like decreased vitamin D production, a decline in melanocyte activity, and a decline in glandular activity can contribute to overall skin health, they do not directly result in increased skin damage and infections as prominently as the decrease in immune system effectiveness. Considering the role of vitamin D in bone health and immunity, insufficient levels do impact general immunity, but the primary concern here is the overall weakened immune response in the elderly due to age-related changes.