Heatstroke and Dehydration

What to look out for in hot weather 

In Britain summer is often said to start with the Elderflower blossom and end with the berry. On that basis we’re in the middle of summer, but in this topsy turvy year for weather, June seems to be making up for the spring drought! Nevertheless, pet owners need to be aware of many potential problems associated with summer should it start to behave like one.

Dogs cope with heat less well than cats and this is probably because the ancestor of the cat originated in North Africa. The dog’s recent ancestor was the wolf who lives in cool climes of the northern hemisphere, so it is poorly adapted to cope with heat.


Heatstroke and sunstroke are the same and occur when the body temperature regulatory systems have failed to maintain normal body temperature in a warm environment, causing the body temperature to rise.

Dogs and cats have two approaches to keeping cool:

1. Body functions
  • Panting
  • Sweating
2. Behaviour
  • Seeking shade
  • Reduced activity

Dogs’ and cats’ main body cooling mechanism is through panting and, to a lesser extent, sweating from their pads. During panting, the breathing becomes rapid and short (up to 400 breaths per minute), the mouth is opened, and the tongue becomes enlarged as its blood supply is increased. Panting allows water to evaporate from the surface of the mouth and the respiratory tract and is very efficient at cooling animals.  But as a consequence, panting can cause rapid dehydration too. Dehydrated pets do not have the reserves of water to be lost through panting so their panting becomes inefficient and their temperature starts to rise.

Dogs and cats will seek out shady and cool spots if they become too warm. The freedom for them to enact this behaviour is essential, because the combination of a fur coat and reliance on one principle cooling mechanism alone is not sufficient to keep cool. This is why dogs left in a warm environment where they cannot escape to a cooler spot simply can’t cope. Every year many dogs die as a result of being left in cars which heat up rapidly in the sun and which offer no chance of escape to a cool spot.

Physical exercise generates a lot of heat within the muscles and conversely, rest avoids heat production. Dogs will ordinarily avoid exercise in the heat of the day to avoid overheating, but dogs are also desperate to please their owners and just don’t know when to stop. They just keep running in the heat of the day until they collapse – you’ll never see a cat do that. Actually, you rarely even see a cat pant. Owners need to avoid exercising their dogs in temperatures above 24C; this is often best achieved by walking dogs at dawn and dusk in the summer. If on a walk a dog’s panting becomes continuous, the owner must immediately ensure that their exercise intensity is reduced and they must seek shade and water both to drink and to soak the dog in to help it cool off.

In a warm environment if a dog’s strategies to keep cool are blocked and its body’s mechanisms to keep cool are overwhelmed, its core temperature will start to rise. Panting becomes inefficient as a result of dehydration so the activity of panting starts generating more heat than it is able to lose through evaporation. At this point the core temperature of the body starts to rapidly rise. Owners must be able to recognise the early signs of heatstroke so they can take action to prevent it from progressing to this point.

Typical signs of heatstroke are:

  • panting so rapidly that they can do little else
  • reluctance to exercise and standing still
  • excessive drooling, bright red gums and tongue
  • increased heart rate
  • feels hot to the touch (body temperature may be over 104?F, and up to 109?F)
  • vomiting and diarrhea
  • collapse, coma and death
Puppies, older dogs, and breeds with pushed in faces like Boxers, Bulldogs, Pekes, and Pugs appear more susceptible to heatstroke than other breeds.

Owners can provide first aid for their pets with early signs of heatstroke:

  • immediately stop exercise and find shade and a breeze
  • provide water to drink and if possible soak the dog’s coat to aid cooling
  • ideally immerse the dog’s body in a bath of cold water or a water trough
  • if available put icepacks on the groin area (beware ice-burns)
  • if available rub spirit based alcohol on the paws (avoid naked flames)
  • massage the skin and extend and flex limbs to optimise blood flow and therefore helping to cool the core temperature
  • phone the vet to warn them that you are on your way, and, if you are driving there, do so with the windows down, ensuring the dog is secured without being physically restrained or with the windows up and the air conditioning on cold


Access to good clean water is essential to animals at all times but it’s particularly important when it’s warm. Well hydrated animals can better keep themselves cool compared to those which are dehydrated.

Thirsty pets will drink almost anything and are vulnerable to infection from dirty water contaminated with microorganisms and poisoning from contaminated water. Water that is contaminated with faeces is potentially full of nasty bacteria. In the summer, occasionally lakes and reservoirs will develop surface plumes of blue green algae (Aquatic cyanobacteria) that produce toxins (cyanotoxin) dangerous to humans and all animals but it is dogs that are most commonly intoxicated. Puddles contaminated with anti-freeze, chemicals, or pesticides can be very dangerous to thirsty animals that quench themselves taking in large volumes before they even taste the water.

At the seaside, a thirsty dog will often drink sea water resulting in excessive salt intake which can lead to salt poisoning. This usually only causes vomiting and diarrhoea, but in severe cases it can lead to swelling of the brain, causing incoordination, depression, and fits. Some swimming pools have salt purification systems, but in the pool the salt is sufficiently diluted to not normally cause a problem. Nevertheless, owners should discourage dogs from drinking from pools by ensuring that fresh water is always available in bowls in the garden. Undiluted chemicals are, however, an irritant and can cause stomach ulcers if they are ingested, so containers should never be left open.

Sunscreen poisoning

Sunscreen contains many chemicals which may be dangerous if ingested either in large quantities or small quantities over an extended period. Dogs and cats that lick sunscreen from their owner’s skin over the summer are vulnerable to intoxication. One of the more dangerous components of sunscreen is PABA (a.k.a.para-aminobenzoic acid, 4-Aminobenzoic acid) and ingestion can cause vomiting and diarrhoea, bone marrow changes, and liver damage. Some sunscreens also contain salicylic acid (a.k.a. aspirin) which can cause stomach ulcers and even kidney failure at high doses. Sunscreen intoxication is thankfully rare but for this reason it is generally not a good idea to put sunscreen on pets unless you have a white dog with a pink nose or a cat with white ears. Cats with white ears that become regularly sun burnt have an increased risk of skin cancer on their ears, usually requiring amputation of the ear.

Insect Stings and Bites

In the summer, insects are most active and the risks of bites and stings increases for both pets and owners. Routine flea and tick control regimens will provide cats and dogs with some protection against bites and stings. For cats it is important that any preventative treatments applied are suitable for cats because cats are particularly sensitive to chemicals due to the metabolism of their liver.

Dogs and cats that catch wasps and bees are at risk of asphyxiation following stings and swelling, leading to occlusion of their airways. The more often that they are stung the worse the reactions are likely to get. Dogs can be trained not to catch stinging insects and remote training collars are a very effective tool in this role.

Pets are at risk of intoxication if they lick insect repellents from their owner’s skin.

BBQ poisoning risks

Summer barbeques represent a risk of poisoning to dogs because they are more likely to be thrown scraps outside or to clean up after the event. Onions or garlic eaten by dogs and cats can cause haemolytic anaemia.

Avocados are toxic to a number of animals, including horses, rabbits, fish and mice. The toxic effects are due to the compound persin, which in some animals causes damage to the heart muscle cells leading to heart failure.

The toxicity of avocado to dogs is under question, but until the susceptibility of dogs to persin is further investigated, it’s best to avoid letting your dog eat any.


  • Don’t exercise your dog in the heat of the day
  • If your dog is panting stop exercise and find shade
  • Don’t leave your dog in a car
  • Make sure that your dog always has access to clean water
  • Avoid ingestion of sunscreen, onions, and avocados

There are many ways to help keep your pets cool during the summer months, not least ensuring they have ample shade, access to fresh water, and that they avoid excessive exercise in the warmest periods.

David Chamberlain BVetMed., MRCVS.
Veterinary Consultant to PetSafe®

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