Which of the following symptoms is commonly associated with infection?

Redness is commonly associated with infection because it is a classic sign of inflammation, which often occurs in response to an infectious agent. When the body detects an infection, it triggers an immune response that increases blood flow to the affected area. This increased blood flow brings white blood cells and other immune factors to help fight the infection, resulting in the redness that is often observed.

Other symptoms related to infections may include swelling, heat, and pain, which are also part of the inflammatory response. Therefore, observing redness can indicate that there is an active immune response taking place, suggesting the presence of an infection.

In contrast, options such as increased appetite, dehydration, and weight gain do not typically correlate with infection. Increased appetite is generally not a symptom of an infection, as many infections can actually lead to a loss of appetite. Dehydration may occur due to various reasons, including illness, but is not a direct sign of infection. Weight gain, similarly, is unrelated to the signs of an infection and does not indicate any change in health status related to infectious processes.