24/06/2026
【湿度を軽視しないで！犬の暑熱対策は気温だけでは不十分】
気温だけを見て「今日は大丈夫」と判断するのは危険です。
犬の熱中症リスクを考える上で、湿度は非常に重要な要素です。
犬は人のように全身で汗をかいて体温を下げることができず、主に「パンティング（ハァハァ呼吸）」による水分の蒸発で熱を逃がしています。
しかし、湿度が高いと蒸発が起こりにくくなり、パンティングによる冷却効果は大きく低下します。
研究では、
・湿度35％を超えるとパンティングの冷却効率は徐々に低下
・湿度80％を超えると冷却機能はほぼ失われる
と報告されています。
そのため、
気温25℃・湿度30よりも、
気温18℃・湿度90％の方が危険なケースもあります。
【「早朝や夜なら安全」とは限らない】
SNSでは「犬の散歩は早朝か夜に」とよく言われます。
しかし日本や英国のような地域では、早朝や夜間は湿度が非常に高くなることがあります。
実際に、
・17℃、湿度90％の早朝に熱中症症状を起こした犬
・10℃前後でも湿度80〜100％の環境下でオーバーヒートした作業犬 などの事例が報告されています。
大切なのは「時間帯」ではなく、
・気温
・湿度
・運動強度
・水分補給状況 を総合的に判断することです。
【運動強度も重要】
犬が激しく運動すると体内で大量の熱が作られます。
走る
ボール遊び
自転車引き
ドッグスポーツ などは特に注意が必要です。
熱の発生量が増えれば、その分だけ体外へ熱を逃がす必要があります。
湿度が高い環境ではその放熱が難しくなり、短時間でも危険な状態に陥ることがあります。
【水分補給は命を守る】
犬はパンティングや唾液の蒸発によって大量の水分を失います。
運動中の蒸発による水分損失は、環境条件によって平常時の10〜20倍に増えることがあります。
脱水が進むと、
・唾液量が減る
・パンティング効率が落ちる
・体温調節能力が低下する という悪循環に陥ります。
暑い日はこまめな休憩と給水を心掛けましょう。
【覚えておきたいポイント】
「暑い＝危険」だけではない
「涼しい＝安全」でもない
高湿度は犬の放熱能力を大きく低下させる
低湿度では脱水リスクが高まる
気温・湿度・運動量・水分補給を総合的に考える
「早朝散歩なら安心」という単純な話ではない
犬の熱中症予防には、気温だけでなく湿度にも目を向けましょう。
愛犬の様子をよく観察し、その日の環境に合わせて運動量や散歩時間を調整することが大切です。
HUMIDITY is very important!
✋🏻 ⛔️ STOP focusing on the ambient temperature alone.
Humidity is highly related to hydration and dogs dissipating heat via panting.
There is published research stating that the ideal humidity range for animals is between 30-70% (it varies a little from different sources), and over 35% panting becomes progressively less effective for dissipating excessive body heat, and when the relative humidity exceeds 80% this body cooling mechanism in dogs is negated.
If the air is already saturated with moisture (high humidity), the water v***r from panting cannot ev***rate. This makes panting ineffective, and their core body temperature rises, because they can't cool down efficiently, they pant more, rapidly losing body fluids through heavy respiration and saliva production upto a point, when they then become dehydrated they conserve body water at the expense of higher body heat.
Dry air (low humidity) acts like a sponge, drawing moisture directly from the dog’s breath as they exhale. This constant exposure to dry air depletes the dog's internal moisture levels, making it a constant threat to their hydration.
Dry air drastically increases the risk of rapid dehydration.
Depending on the dog's exercise intensity, and the environmental temperature and humidity, ev***rative water losses may increase 10-20 fold during exercise.
One of the most common pieces of advice shared over social media in the UK (especially by owners/dog walkers/trainers) is to exercise dogs early in the morning or late at night, yet often times that's when the humidity is very high here.
Look at the environmental conditions, not the time, and be aware of your dogs exertion level.
Remember, higher intensity means more internal heat production, which means more excess heat they need to get rid of.
I know one dog who got into trouble last week at 6am, 17°C, humidity 90%, and needed active cooling, I've seen multiple dogs struggle in the morning and late evening... why?
It's important to understand the humidity you have, the intensity of exercise, hydration status, as well as the ambient temperature.
High ambient temperature combined with high humidity is dangerous.
It is less dangerous to have a higher dry temperature with lower humidity around 30-40% which allows for more ev***ration, but dehydration is a risk, so pay close attention to hydration, and intensity within that environment matters.
Hotter ambient temps mean more work to keep cool. Because they rely on a heat gradient, so the difference between the heat of their body, and the temperature outside their body. The closer the dog's internal body temp is to the ambient temp outside the harder it is for them to manage.
Dogs can acclimate to higher temps upto a point, which is different for individual dogs.
Can dogs acclimate to higher humidity like they can higher temperature?...
I don't know the answer to that, I suspect not, atleast not to the extent they can temperature, as their physical limitations would make it much harder and less efficient.
• Example 1:
With a very warm temp of 25°C with a very low humidity of 25-30% dogs can dissipate more heat through panting than at 18°C with 85-90% humidity which can be more dangerous.
• Example 2:
I went out for a walk on my own at 6pm, temp was 27° with cloud cover (no direct sun), humidity was 40%, there were multiple dogs out walking, not chasing balls or anything high intensity, just walking, they were all fine, in a temperature some people would crucify their owners for and tell them they should be out early or later.
By 10pm the temp had dropped to 19°, but the humidity was 85%, it felt worse.
I would have been walking my own dog at 6pm on that day, because I knew my dog, and managed hydration, giving him a drink of water every 15-20 mins can go a long way to staying in the green.
• Example 3:
I've seen multiple dogs running in harness over the years in temps around 10°C, but humidity above 80%, often in the 90s, even pushing 100%, get extremely hot, sometimes needing active cooling.
I once spoke with a musher about heat injury after an incident, this person always trained very early morning, when it was warm often in these high humidities, had had multiple cases of overheating over the years... I wonder why!
If you're honest, and understand what you're looking at, why are some dogs struggling in the heat when the humidity is in their favour, while others are doing fine?... there are various factors but often because owners push their dogs too far, for too long, before stopping for a break and re-hydrating, they get hotter, dehydration increases, they get hotter.
Is the answer simply to "go out early" ?
No one is saying exercise your dogs in the hottest, sunniest part of the day in temps they are not acclimated for, but "early" or "late" is not necessarily safer, there can be an area in between that may be better.
Just saying "exercise early" with no context can be dangerous.
Higher temperatures are a well known risk. Moderate temperatures with high humidity, combined with higher intensity exercise are less well known, it's a bit more sneaky you could say, but it can get a dog in trouble pretty quick.
But again, good hydration management is a huge part of keeping dogs safe when temps rise.
There's a LOT to heat tolerance.
"In dogs, the nasal turbinates provide a large surface area for water ev***ration, from the moist mucous membranes, thereby playing an important role in heat dissipation through panting, while hypersalivation increases the ev***rative efficiency through ev***ration from the oral mucous membranes and the tongue. With high environmental temperatures and increased relative humidity (>35%), panting becomes progressively less effective for dissipating excessive body heat, and when the relative humidity is >80%, this body cooling mechanism in dogs is negated. In addition, with a progressive increase in core body temperature, metabolic derangement ensues, cardiac output decreases, leading to heat dissipation failure, aggravating body heat accumulation. When hyperthermia, combined with dehydration, progresses, cutaneous and splanchnic blood pooling results in decreased circulating blood volume and hypotension.... "
https://pmc.ncbi.nlm.nih.gov/articles/PMC5800390/
"Since dogs have minimal sweating capacity, thermoregulation relies primarily on ev***rative mechanisms through panting. Heat, humidity, and hydration are thought to impact the dog’s ability to thermoregulate. High ambient temperatures decrease the heat gradient from the dog to the environment and add external heat to the dog. Humid conditions impair effective ev***rative cooling. Humid environments can contribute to heat stress. In addition to the environmental factors of heat and humidity, the dog’s adaptation to environmental conditions (also called acclimatization), overall fitness/conditioning and state of hydration are thought to be major factors that impact heat tolerance. Canine thermoregulation involves the inhalation of cooler, dryer air through the nose and mouth, which causes ev***rative heat loss from the nasal and oral mucosa and tongue, and the exhalation of hotter, moister air. In conditions in which the rate of heat generation is greater than the rate of heat dissipation, increased salivation and lingual blood flow allow for convection and ev***rative cooling. Ev***rative cooling results in electrolyte-free water loss (estimated at ~10 mL/kg/h) which can contribute to dehydration.
In hydrated dogs, salivary loss is estimated at 7 mL/kg/h during exercise. In dehydrated dogs, the amount of water lost to cooling was approximately 7% lower than in hydrated dogs, but salivation was reduced by over 90%.
As dehydration increases, the availability of water for ev***ration, salivation, and circulation will be diminished; heat tolerance and physical, mental, and olfactory performance will be reduced.
https://pmc.ncbi.nlm.nih.gov/articles/PMC5662554/
"The most remarkable increase in water loss observed in working dogs is due to the increase in ev***ration from the mouth and respiratory tract. Depending on the dog’s exercise intensity, and the environmental temperature and humidity, ev***rative water losses may increase 10- to 20-fold during exercise.
At cold temperatures, the air a dog breathes in has very little moisture in it. When this cold air reaches the lungs it is saturated with water so that about 6% of every exhaled breath is water. In warm climates the inhaled air is more nearly saturated with water and so the dog loses less water from its lungs with each breath. However, since dogs pant to cool themselves off, water loss through the ev***ration of saliva often leads to ev***rative losses in warm conditions equal to or in excess of those seen in cold
environments...
Dehydration is almost always easier to prevent than it is to treat."
https://www.academia.edu/69683140/Hydration_Strategies_for_Exercising_Dogs?fbclid=Iwb21leASl0_xjbGNrBKXT9GV4dG4DYWVtAjExAHNydGMGYXBwX2lkDDM1MDY4NTUzMTcyOAABHh69bl4iFpdUuNHMdj85Ohg8-sAoTH3mmIJFbA4XeF5WukBr8BFV7T0l6x-A_aem_ichxhXIUlUKUHUz2B_sutg
"Even more concerning, in our latest paper we reported the highest daily "feels like" temperature (this is "wet bulb globe temperature", which takes into account air temperature, humidity, wind speed and solar radiation) recorded at the nearest weather station to each HRI event we studied. The average (median) temperature was just 16.9°C. The lowest temperature was 3.3°C (for an exercise induced HRI case), whilst the highest temperature was 23.1°C. These are not high temperatures...
When judging temperature conditions for your dog, you also need to consider how temperature is being measured... "
https://heatstroke.dog/category/research-news/
● Related Posts:
• Differences in Heat Tolerance between dogs and factors to consider
https://www.facebook.com/share/p/1ELixL5xjQ/
• When is it Too Hot?
https://www.facebook.com/share/p/1JRyDYfhBK/
• Hydration
https://www.facebook.com/share/p/1cjGDs9qhC/
