What is a key sign of dehydration in adults?

Decreased urine output is a key sign of dehydration in adults because it indicates that the body is conserving water due to insufficient fluid intake or excessive fluid loss. When a person is dehydrated, the kidneys respond by retaining as much fluid as possible, which results in reduced urine production. This physiological response is a protective mechanism to help maintain fluid balance and ensure that vital organs continue to receive adequate hydration.

In contrast, the other signs listed are not indicative of dehydration. Increased blood pressure may not be directly associated with dehydration; in fact, dehydration can lead to decreased blood volume, which might result in lower blood pressure in some cases. Weight gain is generally unrelated to dehydration and typically reflects fluid retention rather than loss. Redness in the skin can occur for various reasons, including inflammation or allergic reactions, but it is not a specific indicator of dehydration. Understanding these distinct responses helps in assessing fluid status in individuals effectively.