Signs of Dehydration

Updated: September 25, 2026 · Reviewed by Taylor J. Graber, MD

Extreme heat is common across much of the Southwest and West Coast for much of the year, and many of us end up adjusting our routines to cope with it. Limiting outdoor time, using sun protection, and prioritizing hydration are a few ways to help stay safe and healthy in hot weather.

But what about when that's not always possible — when you have to be out in the heat for a while, or don't have easy access to water? How do you know if you're becoming dehydrated?

Here are a few key signs to watch for.

Dry mouth and skin

As the body becomes dehydrated, blood vessels to the skin and mucous membranes constrict to conserve water, which can leave skin, lips, and your mouth feeling dry.

Dark urine

The more dehydrated you are, the less urine your kidneys produce as they work to conserve fluid — and the urine that is produced tends to become more concentrated and darker in color.

Fainting and light-headedness

When the body doesn't have enough fluid, the heart pumps less blood with each beat. That can lower blood pressure and reduce blood flow to the brain, leading to light-headedness, dizziness, or fainting.

Fatigue

Ongoing dehydration can also contribute to lower cardiac output and reduced blood flow to tissues, which may leave you feeling tired, fatigued, or low on energy.

When to seek help

An IV may help relieve mild dehydration symptoms in as little as 30 minutes for some people. But if you suspect your dehydration is severe, call 911 or seek emergency medical care right away. Signs of severe dehydration include confusion or disorientation, a rapid heartbeat or breathing, fever, or loss of consciousness.

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