Dog cold exposure: hypothermia, frostbite, and which dogs actually need a coat

Quick answer

Cold tolerance is decided by coat type, body size, body fat and age, not by how tough a dog looks. Check the dog in front of you, not the breed stereotype.

Dogs do not all experience the same weather. A thickly double coated northern breed and a lean single coated sighthound standing in the same field are in two different environments, and the temperature on your phone tells you almost nothing on its own.

Three factors change cold from uncomfortable to dangerous: wind, wet, and time. A dry dog out of the wind copes with far more cold than the same dog soaked and standing still, because water displaces the insulating air trapped in the coat and wind strips it away.

• Wet plus wind is the combination that causes hypothermia, not low temperature alone.
• Small, lean, thin coated, very young, very old and unwell dogs lose heat fastest.
• Shivering that stops in a cold dog is a deterioration, not an improvement.
• Rewarm the trunk, never the extremities first, and never with direct heat on skin.
• Antifreeze and ice melt salt injure more dogs each winter than the cold itself.

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A cold dog that has stopped shivering is in serious trouble.

Shivering is the body generating heat. It stops when the muscles are too cold to work and when the animal can no longer compensate, so a dog that was shivering and now is not, and is quiet, stiff, stumbling or unresponsive, has moved from mild to moderate or severe hypothermia. Wrap the trunk, get the dog into warmth and go to a vet immediately. Do not rub the legs, do not immerse the dog in warm water, and do not apply a hot water bottle, hair dryer or heat pad directly to the skin.
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Decide in 60 seconds

Why cold does what it does

A dog stays warm by producing heat and by holding on to it. Cold overwhelms one or both.

Conduction takes heat straight out of the body into whatever the dog is touching. Frozen ground, snow, concrete, a metal crate tray or a wet car boot floor pull heat continuously from a lying dog, and a short legged dog loses it through the belly as well as the feet.

Convection is wind. Moving air constantly replaces the warmed layer next to the skin, and it forces its way through the coat and destroys the still air layer that provides the insulation. This is why a still cold day and a windy one of the same temperature are not comparable.

Evaporation removes heat as water leaves the coat. A wet dog is losing heat by evaporation and by conduction at the same time, and its coat has lost most of its insulating value while it is soaked.

Heat production falls when the dog stops moving. A dog trotting generates a lot of heat; the same dog standing while you talk to someone generates very little, and the cold then wins.

Against that, the dog constricts the blood vessels in its skin and extremities to protect the core, raises its coat, curls up to reduce exposed surface area, and shivers. All of those buy time. Shivering is the expensive one, because it burns energy quickly, and a thin dog or a puppy runs out of fuel to burn.

When the core temperature falls, the heart slows, the muscles stiffen, the brain slows and shivering stops. That is the transition point from a cold dog to a medical emergency.

Which dogs actually need protection

Coat type is something you check with your hands, not something you read off a breed name. Part the coat: a dense woolly layer under the top coat is insulation, a single layer of hair on skin is not.

Coat structure, not coat length. Part the hair. A double coated dog has a dense, soft, woolly undercoat beneath the guard hairs, and that layer is the insulation. A single coated dog has guard hairs on skin, however long or shiny they look. Single coated breeds include most sighthounds, pointers, boxers, bull breeds, dobermanns, dalmatians, and many small companion breeds, plus most poodle coated crosses once clipped.

Size. A toy breed loses heat much faster than a large dog with the same coat. It also sits closer to the ground and to cold, wet surfaces.

Body condition. A lean dog has less insulating fat and less energy reserve for shivering. Whippets, greyhounds, salukis and lurchers combine minimal fat with a single coat and a large skin surface, and they are the group most likely to be in genuine trouble on a winter walk.

Age. Puppies have poor temperature control and a large surface area for their mass. Elderly dogs have less muscle, respond more slowly, and often have arthritis, which cold stiffens further.

Health. Hypothyroidism, Cushing's disease, diabetes, kidney disease, heart disease and any recent illness all reduce cold tolerance. So does recovery from anaesthesia, which is why dogs come home from surgery cold.

Recent clipping. A clipped dog has lost its insulation until the coat regrows, and a double coated dog that has been shaved may not regrow a proper undercoat at all.

Which dogs do not need a coat. A well conditioned, dry, active northern or mountain breed with a full double coat is usually better off without one. A coat on such a dog compresses the undercoat, reduces the trapped air that provides the insulation, and traps moisture against the skin.

Hypothermia, stage by stage

Mild. Shivering, seeking shelter, curling tightly, lifting or shaking feet, ears back, whining, slowing down, wanting to turn for home. The dog is compensating and will recover with warmth and drying.

Moderate. Shivering becomes violent and then stops. Muscles stiffen, movement becomes clumsy, the dog becomes quiet and withdrawn, breathing and heart rate slow, gums become pale. This dog needs veterinary care.

Severe. Unresponsive or barely responsive, rigid, very slow or undetectable breathing and pulse, fixed dilated pupils, cold to the core. This is a resuscitation situation and needs a vet immediately, with careful controlled rewarming that is not safe to do at home.

The transition owners miss is the second one. Shivering stopping feels like the dog has settled. It is the opposite.

Rewarming without making it worse

Get the dog dry. Towels first, then more towels. Removing water removes the largest ongoing heat loss.

Warm the trunk, not the limbs. Wrap the chest and abdomen in warm dry blankets or towels. Warming cold limbs first opens the blood vessels in them and returns cold, acidic blood to the heart, which can drop the core temperature further and destabilise the heart rhythm.

Never apply direct heat to skin. Hot water bottles, heat pads, radiators, hair dryers and car heaters aimed at the dog all cause burns, and a cold dog with numb skin will not move away. Any heat source must be wrapped in several layers and never in direct contact.

Do not put a hypothermic dog in a bath. Immersion rewarms the periphery fastest, which is exactly the wrong order, and a weak dog can inhale water.

Warm the room and the air, and use your own body heat by holding the dog against you under a blanket.

Offer warm, not hot, water only if the dog is fully alert. Never pour anything into the mouth of a dog that is dull or unresponsive.

Never give alcohol. It causes peripheral vasodilation and accelerates heat loss, and the folklore about brandy is exactly backwards.

Transport warm. Run the car heater before you load the dog, and keep the wrapping on.

Frostbite

Frostbite happens where blood supply is furthest from the core: ear tips, tail tip, footpads and toes, the scrotum in males, and the nipples in a lactating bitch. It is more likely in a dog that is already hypothermic, because the body has shut down peripheral circulation to protect the core.

Early. Skin pale, grey or bluish white, cold, hard, and often waxy. It does not hurt at this point, which is why it is missed.

On rewarming. Red, swollen, and painful. Pain here is a good sign, because it means there is living tissue.

Days later. Blisters, then dark discoloration, then a clear line between living and dead tissue. That demarcation takes days to weeks, so nobody can tell you the extent of the damage on day one.

Do not rub frostbitten tissue, and never rub it with snow. Ice crystals in the tissue shear cells apart when the area is rubbed.

Do not rewarm if there is any chance of refreezing, for example if you are still outdoors and far from the car. Refreezing thawed tissue causes far worse damage than leaving it frozen until you can keep it warm.

Rewarm gently with warm, not hot, water or warm packs over cloth, and take the dog to a vet. Frostbite is painful, it becomes infected easily, and pain relief is needed.

Equipment that helps, and how it fails

Track weight through the winter as well as walks. A thin dog burning energy to stay warm can quietly lose more condition, and less fat means less insulation next time.

Coats. The useful ones cover the chest and the belly, not just the spine, because the belly is where a small dog loses heat to the ground and the snow. They need a waterproof and windproof outer layer over an insulating layer, they must not restrict the shoulder, and they must not be so tight at the neck or chest that they rub. A soaked fabric coat left on a dog is worse than no coat, because it holds cold water against the skin.

Boots. Genuinely useful on gritted pavements, on sharp ice, and for dogs with cracked pads. They need proper fitting and a few sessions of training indoors, because a dog that has never worn them walks like a cat in socks and can strain something. Check for rubbing at the dewclaw and above the hock, and take them off indoors.

Paw wax or balm. Reduces salt contact and ice balling between the toes in furry footed dogs. Not a substitute for rinsing the feet after a walk.

Rinse and dry after every winter walk. Lukewarm water over the feet, then dry between the toes. This removes ice melt salt, which is both a chemical irritant to skin and a hazard if the dog licks a large amount off its feet.

Bedding off the floor. A raised bed or a thick insulating pad prevents continuous conduction into a cold floor. This matters most for thin, old and arthritic dogs.

Outdoor shelter, if a dog is outside at all. Raised off the ground, small entrance turned away from the prevailing wind, dry insulating bedding such as straw rather than blankets, which absorb moisture and freeze. Heat lamps in kennels are a fire risk and a burn risk. A dog that cannot be kept warm outdoors should be indoors.

Heated pads. Only thermostatically controlled products designed for animals, only over a cover, never for a dog that cannot move off them, and always with a chew resistant cable.

Visibility gear. Winter walks happen in the dark. A reflective or lit coat or collar is a safety item in its own right.

The winter hazards that are not cold

Antifreeze. Ethylene glycol tastes sweet, is lethal in small quantities, and causes kidney failure. A dog that has licked a puddle on a driveway, a garage floor or a car park needs veterinary care immediately, before any signs appear, because treatment is time critical.

Ice melt and rock salt. Irritates and cracks pads, and if ingested in quantity from the feet or from a spill it raises blood sodium and causes vomiting, tremors and seizures.

Frozen water. Dogs go through ice on ponds and canals every winter. Do not throw anything near frozen water and do not go in after a dog.

Cold water swimming. A dog that swims in cold water can develop an acutely painful limp tail that hangs down and is tender at the base. It is a muscle injury, it needs pain relief, and it usually resolves with rest.

Cars. A parked car in winter becomes an efficient cold box, not a shelter.

The routine that prevents it

What never to do

Do not assume a dog with fur is protected. Coat type, size, condition, age and health all override the fact that a dog has hair.

Do not shave a double coated dog for the winter, and do not clip one short expecting the coat to come back the same.

Do not leave a coat on a wet dog.

Do not apply direct heat, a hair dryer or a bath to a hypothermic dog.

Do not rub frostbitten tissue, and never with snow.

Do not force a shivering, reluctant dog to keep walking to warm up. A dog that wants to go home in the cold is usually right.

Do not leave a dog in a parked car in winter.

Do not judge frostbite severity in the first days and decide it is minor.

When to get help

Go immediately for a dog that has stopped shivering and is quiet, stiff, stumbling or unresponsive, for pale or grey gums, or for very slow breathing.

Go immediately after any suspected antifreeze contact, before signs develop.

Go the same day for hard, pale or waxy skin on ears, tail or pads, for skin that has become red, swollen and painful after cold exposure, for a limp painful tail after a cold swim, or for a dog that will not bear weight after a walk on ice.

Bring what you know: how long the dog was out, whether it was wet, whether it was immersed, what surfaces it lay on, whether shivering stopped and when, and anything it may have licked or eaten.

Recovery looks like a dog that is dry, warm, moving normally and interested in its dinner. Keep checking ears, tail and pads for several days, because frostbite damage declares itself late.