Which of the following is true about the role of normal flora on the skin?

Normal flora, or the microbial community that resides on the skin, play a significant role in maintaining skin health and function. They contribute to the skin's barrier against pathogens by competing for resources and space, which helps to limit the colonization of harmful microorganisms. However, under specific circumstances—such as breaks in the skin, immunocompromised states, or alterations in the skin's microbiome—the normal flora can opportunistically cause infections. This characteristic of normal flora reflects their ability to adapt to different environments and conditions, leading to potential pathogenicity while typically residing commensally.

In contrast, the other options do not accurately describe the role of normal flora. They are not universally harmful; instead, they generally provide a protective benefit. Additionally, while they contribute to preventing infections, it is incorrect to claim they completely do so since they can sometimes become pathogenic. Lastly, normal flora indeed exist on healthy skin and are crucial for the skin's physiological processes.