Today, the heat index here in North Carolina was 105°F.
Frustratingly, I had to bear the heat to run a few errands and on my way home I saw something that made me so very frustrated – a man walking his dog.
Not only was this a man walking a dog, this man was walking a SAINT BERNARD.
Now, the Saint Bernard is NOT a North Carolina breed.
What I mean by that is that this is not a dog that will thrive in the climate that North Carolina has to offer. It’s too hot, it’s too humid, and this is a breed that does not tolerate either of these conditions well.
The Saint Bernard was bred in a location where the average annual high temperature is 36°F and the hottest day of the year is around 53°F.
Think about that for a moment.
Today was 52° hotter than the hottest day where this dog was bred to live. Today was almost TWICE as hot as the hottest day this dog was bred to live in.
But, it’s not only dogs like the Saint Bernard that suffer in the summer heat.
When it’s hot outside, the heat of the asphalt on a dog’s feet is extreme.
Want an example? When the air temperature outside is just around 100°F, the asphalt that you are asking your dog to walk barefoot on is around 158° F.
What happens at 158°F or 70°C? A study at Rush Medical College found that after 300 milliseconds of exposure at 70°C lethal injury to red blood cells began to occur ¹.
This incredibly high level of heat will cause burns, blisters, and an intense amount of pain to your dog’s paw pads.
Don’t think it could be that bad? Hold the back of your hand against the hot asphalt for 10 seconds without moving it and see for yourself.
It’s not just the temperature of the asphalt that you need to worry about, however, it’s also the air temperature.
If an outdoor temperature is 100, it isn’t uncommon for the heat index to be much hotter.
The heat index is a combination of the air temperature and the humidity and it refers to the temperature that the body feels when outside. This is also referred to as the “apparent” temperature.
So, when the outside temperature is 100°F outside, a relative humidity level of 50% will make the apparent temperature 120°F ².
So not only are you asking your dog to walk on asphalt that is 158°F, but you are asking them to breathe, to walk, to exercise, in an apparent temperature of 120°F assuming that the humidity is at 50%.
Now, relative humidity is a number, a percentage, but what does it mean?
Absolute humidity is a ratio of water vapor mass over dry air mass in a given volume of air. Now, the ratio of this number (the absolute humidity) to the highest possible level of absolute humidity for the current air temperature.
This probably sounds like a lot of science speak, so let me simplify…
If the relative humidity is 100% it means that the air is as saturated as it can get with water molecules. This saturation causes the air to feel much warmer than the actual temperature outside – what we referred to as “apparent temperature” before.
But why does the relative humidity make it feel hotter outside?
When we are hot, our bodies try to cool themselves through sweating. As the sweat is evaporated from our skin, we cool down and our body temperature comes down.
Now, if the air is already 100% saturated with water vapor it cannot possibly take up any more, so the sweat that our skin produces to cool the body cannot be evaporated. We cannot cool down.
If the relative humidity is 50%, then our bodies will still attempt to cool itself through sweating, but the sweat from our skin will evaporate slower than it would at lower relative humidity due to the air holding 50% water vapor already.
So, we know that the body is capable of cooling itself more efficiently in lower relative humidity, but how does relative humidity affect our respiration?
The higher the relative humidity, the harder the body has to work to cool itself down.
The harder the body has to work to cool itself down, the more energy it uses to perform everyday functions.
The more energy is being used, the more oxygen is being used, and the shorter of breath we can feel.
It is also purported that the more humid air becomes, the denser it becomes, therefore causing increased airway resistance as we breathe – once again, requiring more effort and energy.
So, as the temperature increases, the body works harder to cool itself. As the humidity increases, the body works even harder.
Too much humidity and we push our bodies too far. Too little humidity and dry air causes irritation, sucks moisture from our skin, and dries out our sinuses. So, we have to find a balance between too little and too much humidity.
The relative humidity level at which the human body is most comfortable is 45%
So, how does this affect our dogs?
When you walk your dog outside when the temperature is 100°F and the humidity is 50%, the apparent temperature is 120°F.
In 120°F with a higher than optimal humidity level, your dog is having to work hard to cool it’s body down to a healthy temperature. They are not only fighting against the temperature, but they are also fighting harder to take in enough oxygen to fuel the cooling process.
But our dogs don’t sweat…do they?
Dogs do actually have a few sweat glands, but most of them are located on their paw pads for the most part. The most efficient method of cooling used by our dog’s bodies is panting.
When our dogs pant their rate of breathing increases some tenfold and with each open-mouthed breath, water is evaporated and heat is pulled from the body in the form of water vapor.
As your dog pants to cool themselves down, their effort expended increases, just as it is when our bodies try to cool themselves in higher than normal temperatures.
If, however, the temperatures outside are so hot that a dog is unable to cool themselves quickly enough, they succumb to heat exhaustion.
Clinically, a body temperature of 106°F is exemplary of heatstroke. This temperature can vary slightly.
When experiencing heatstroke, a dog can also experience multiple organ failure and death.
So just how hot is too hot? At what point are our dogs unable to cool down?
The rate at which a dog’s body temperature rises and cools is variable and it depends on a dog’s individual size and health.
A dog’s normal average temperature is between 100°F and 102°F.
When your dog’s temperature reaches around 104°F their bodily cooling system is struggling to cool the body.
At 104°F your dog is already suffering from heat exhaustion.
By 105°F your dog’s tongue will loll out of the side of their mouth as they pant harder. This is a method of increasing the surface area that can be utilized to cool the body down.
By 106°F to 107°F, the heart will start to race, dizziness, weakness, vomiting, diarrhea and bright red gums may be seen. Your dog may collapse.
By 108°F to 110°F, irreversible organ damage takes place.
Complete heat stroke can happen within 10 to 15 minutes.
The rough guesstimate for a temperature in which a dog’s body temperature will begin to rise is 90°F.
There is no set time period for how long a dog can withstand a certain temperature outdoors. This is due to the fact that there are so many factors that go into how quickly your dog’s body temperature will rise. These factors include the relative humidity, the outdoor temperature, your dog’s coat length, your dog’s coat type, your dog’s snout length, your dog’s age, your dog’s health, and your dog’s breed.
A general rule of thumb is to test the asphalt temperature with the back of your hand as instructed above. If you can’t hold your hand without moving it for 10 seconds it’s too hot. If it’s too hot for you to walk barefoot on it, it’s too hot.
When it comes to temperature and humidity, keep an eye on that chart referenced above, or find it here. Your dog’s normal body temperature is 100°F to 102°F, if it gets above 103°F then your dog is going to begin suffering negative effects from the heat. So, to be safe, walk your dog only in apparent temperatures are at a level that your dog’s cooling system can cope with.
For example, if the outdoor temperature is 88°F and the relative humidity level is 12%, then your apparent temperature is going to be around 82°F – a sustainable temperature for your dog to exercise in.
Don’t forget that as your dog exercises in the heat, the muscle movement that results also causes an increase in body temperature.
Some studies have shown that working dogs that have been conditioned to work for long periods of time and in quite warm temperatures, can reach body temperatures of 108°F without any signs of heatstroke. Keep in mind, though, that most dogs are not conditioned to such extremes and rigorous exercise can result in similar body temperatures, but a lack of conditioning results in the detrimental effects of heatstroke.
So….what does all of this mean?
Keep your dog inside when it’s hot outside!
Walk before sun-up and after sun-down.
Always carry water.
Keep a cell phone on hand with an emergency vet number.
Know your dog’s limits.
Pay attention to the signs.