Which of the following is a common sign of dehydration in patients?

Dehydration occurs when the body loses more fluids than it takes in, leading to a variety of symptoms as the body's systems begin to struggle without adequate water. Dry mouth is a direct consequence of the body conserving water, causing the mucous membranes to become less moist. Decreased urine output is also a significant indicator of dehydration, as the kidneys retain fluid when the body is short on water, resulting in more concentrated and less frequent urination. Together, these signs clearly point to a state of dehydration where the body is attempting to maintain essential functions despite a fluid deficit.

In contrast, options that suggest increased appetite and energy do not align with dehydration, as the lack of fluids usually leads to fatigue and a general sense of malaise. Bright red skin and rash indicate other issues, such as heat exhaustion or infection, rather than dehydration. Furthermore, while frequent headaches can be a symptom of dehydration, they typically appear alongside other signs such as dizziness or dry mouth, making them insufficient as the primary indicator of dehydration in this context. Thus, the presence of dry mouth and decreased urine output stands out as the most telling signs of dehydration among the provided choices.