Dehydration in Cats: Signs, the Skin Tent Test and What to Do

Cats evolved from desert-dwelling ancestors and are good at conserving water, which is a mixed blessing. They concentrate their urine well and often drink surprisingly little, but they also hide illness, so a cat can become seriously dehydrated before anything looks wrong. Knowing the signs, and what to do about them, is one of the most useful skills a cat owner can have.

What Dehydration Actually Is

Dehydration means the body is losing more fluid than it takes in. Water is essential for circulation, kidney function, digestion and temperature control, so a shortfall affects everything. Mild dehydration may cause few visible signs; moderate to severe dehydration is a medical problem that needs a vet.

Common Causes

• Vomiting and diarrhoea: fluid is lost faster than it can be replaced.
• Chronic kidney disease: failing kidneys cannot conserve water, so affected cats urinate more and are prone to dehydration.
• Diabetes and hyperthyroidism: both can increase urination and fluid loss.
• Fever, heat or overheating: losing water through panting and the skin.
• Not eating or drinking: pain, dental disease, nausea or stress can all reduce intake.
• A dry-food-only diet: wet food is roughly 75-80% water, while dry food contains only a small fraction, so cats on dry food must drink more to compensate.

Signs to Look For

• Lethargy and less interest in play or food.
• Dry, tacky or sticky gums instead of moist, pink ones.
• Sunken, dull eyes.
• Reduced urination or small, dark, strong-smelling urine. A smaller litter box clump than usual is a clue.
• Constipation or hard stools.
• Loss of skin elasticity (see below).
• Panting, which in cats is never normal at rest and always deserves attention.

The Skin Tent Test

Gently lift a fold of skin over the shoulder blades, then release it. In a well-hydrated cat it snaps back almost immediately. In a dehydrated cat it returns slowly, or stays "tented" for a moment or more.

The test is a rough guide only. Skin elasticity naturally declines with age, thin or recently slimmed cats can look tented when they are fine, and overweight cats can snap back quickly even when dehydrated. Veterinary teaching also notes that obvious skin changes do not usually appear until dehydration is already significant, so a normal result does not rule it out. Watch the video below to see how a vet assesses skin turgor.

VETgirl demonstrates how skin turgor is evaluated in a cat.

A Quick Gum Check

Lift your cat's lip and look at the gums. They should be pink and slick with saliva. Press a fingertip against them until they blanch, then release: colour should return in about one to two seconds. Pale, grey or dry gums, or a slow return, mean you should call a vet promptly.

When It Is an Emergency

Contact a vet the same day, or go to an emergency clinic, if your cat:

• Has been vomiting or having diarrhoea for more than a day, or cannot keep water down.
• Has a persistent skin tent, sunken eyes or pale, dry gums.
• Is weak, collapsed or unusually sleepy.
• Has not urinated in 24 hours. In male cats especially, a blocked bladder is life-threatening.
• Is a kitten, a senior or has a known kidney, heart or endocrine condition.

Do not try to force water into a very weak or vomiting cat; there is a risk of inhaling it. Dehydration of any real degree is treated with fluids, and the cause needs to be found as well.

How Vets Treat It

Your vet will examine your cat, may run blood and urine tests to look for the underlying cause, and will rehydrate them. Mild cases may get fluids under the skin (subcutaneous fluids). More serious cases need intravenous fluids in hospital, with careful monitoring because some cats, especially those with heart disease, cannot tolerate fluids too fast.

Cats with chronic conditions such as kidney disease are sometimes prescribed regular fluids at home. If that applies to you, ask your vet to demonstrate in person first. The Feline Veterinary Medical Association's Cat Friendly Homes programme has a calm, step-by-step tutorial that many owners find a helpful reminder afterwards.

How to give subcutaneous fluids to a cat, as prescribed by your vet.

Helping Your Cat Drink More

• Feed some wet food. It is the easiest way to add water to a cat's day, and many cats take extra if you stir in a little warm water.
• Offer several bowls in different rooms, away from the litter box and food. Wide, shallow bowls are kinder to sensitive whiskers.
• Try a fountain. Plenty of cats prefer running water.
• Keep water fresh, refilling and washing bowls daily.
• Make drinking easy for seniors, with low-sided bowls on every floor of the house.

The Short Version

1. Cats hide illness, so dehydration is easy to miss.
2. Check gums, energy, eyes and litter box output; the skin tent is a rough guide only.
3. Vomiting, diarrhoea, no urine or weakness need a vet quickly.
4. Encourage drinking with wet food, fountains and bowls placed around the house.

This article is general information, not veterinary advice. If you are worried about your cat, contact your vet.