What are common signs of dehydration?

Dehydration commonly shows up as dark yellow or amber urine, which is one of the earliest and most reliable indicators. Thirst is an obvious sign, though by the time you feel thirsty you're already mildly dehydrated. Other frequent symptoms include dry mouth, fatigue, dizziness, and headaches. You may also notice decreased urine output, dry skin, and difficulty concentrating. In more severe cases, dehydration can cause rapid heartbeat, rapid breathing, sunken eyes, and confusion. In infants, a sunken fontanelle (soft spot on the head) and lack of tears when crying are key warning signs. Severe dehydration requires immediate medical attention.