It’s a commonly held belief that “dogs don’t sweat except on their feet”, but that’s not true and in fact it’s been known that dogs sweat all over and that it likely makes a significant contribution to how they control their body temperature when the weather gets hot.
Dogs are like us. They have two different types of sweat glands. Eccrine and Apocrine. Eccrine sweat glands such as are found on the dog’s foot pads open directly onto the skin surface and have no hairs associated with them. Apocrine sweat glands are found at the base of hair follicles – so only in hairy areas.
Horses have Apocrine sweat glands all over the body in hairy areas which constitute over 95% of their sweat glands, but only have Eccrine glands in a few hairless areas such as the frog and under the tail.
Dogs have MORE Apocrine sweat glands (sweat glands in hairy areas) than Eccrine sweat glands, which are limited to the footpads and nose.
Dogs may lose 20% of their total heat by sweating at an ambient temperature of ~31°C.
So, dogs DO sweat and this is not limited to the feet. In fact, they lose significantly more heat by sweating through hairy skin than their footpads or nose……It’s just harder to see the sweat under the hair!
Understanding how dogs control their body temperature when it’s hot
Lots of misunderstandings circulating on this topic. Apologies for the graph but I hope I can show why it’s needed and explain it clearly. This is some data redrawn from the work of the great animal physiologist Charles Richard (CR) Taylor (1939-1995). This shows how dogs lose heat in different environmental conditions (ambient temperatures).
Key principles
The dog’s body temperature is around 38°C. The ambient temperatures in which the dog was studied ranged from warm (21°C) to very hot (41°C).
CONVECTIVE HEAT LOSS – this is the way in which heat moves from the skin (or coat surface) to the surrounding air. No evaporation or direct contact is involved. The thicker the coat the slower they lose heat. A dog’s thick coat insulates! Keeps heat in! Makes it hotter.
EVAPORATIVE HEAT LOSS – reduction in temperature caused by evaporation of water from the respiratory tract (breathing, panting) or evaporation of sweat.
Metabolism – Chemical reactions in the body that produce heat.
Exercise – Muscles are not very efficient at turning stored food energy into heat. When dogs exercise around 80% of the energy they use ends up as heat, the majority of which they must try and get rid of.
A rise in body temperature from ~38°C to 40°C can trigger heat illness.
Ambient = surrounding air temperature
How do dogs control body temperature?
21°C AMBIENT TEMPERATURE – Dogs lose a lot of heat by convection because there is a big difference between their body temperature and the surrounding air. Only a fraction of the total heat lost is by evaporation.
26-31°C AMBIENT TEMPERATURE – Convective heat loss is reduced as the surrounding air is closer to the dog’s body temperature. But even at 31°C air temperature around the dog, only around 40% of the total heat loss comes from evaporation and only 20% from respiratory heat loss. 20% comes from the evaporation of sweat from the pads, nose and apocrine glands at the base of hairs (see above – dogs do sweat under their coat).
36°C AMBIENT TEMPERATURE – As the air temperature around the dog is now close to skin temperature (which is usually a few °C lower than central body temperature), the potential for heat to be lost by convection is small and whilst sweating continues, heat loss from panting now accounts for 75% of the heat dissipated (got rid of).
41°C AMBIENT TEMPERATURE – The dog is now getting rid of almost twice as much heat as it was having to at 31°C. The air surrounding the dog is now heating it up (heat is moving from the environment into the dog). Convective heat loss is now zero. 90% of heat loss comes from panting.
Summary
Whilst panting is efficient at cooling dogs down, it places great stress on the body, especially on the heart and respiratory systems. That’s why it’s important that old dogs, overweight dogs, brachycephalic breeds and dogs with heart or respiratory problems should not be allowed to stay panting and should be kept cool or cooled down when they start to pant!
SHORT VERSION – When the surrounding air temperature is ~31°C or below the main way dogs get rid of the heat they produce in their bodies from metabolism at rest or exercise is by CONVECTION (loss from the surface – through the skin and coat, so the thicker the coat the slower they lose heat). Respiratory heat loss from PANTING only starts to take over as the main mechanism once the dog’s temperature and ambient temperature converge i.e. around 36°C. The ambient temperature at which dogs start to pant may be lower in overweight dogs, dogs with thick coats, large dogs, dogs that are not acclimated to the heat, unfit dogs, brachycephalic breeds, dogs with respiratory disease, older dogs and dogs with heart conditions.
References
Aoki, T and Wada, M (1951) Functional activity of the sweat glands in the hairy skin of the dog. Science 03 Aug, Vol. 114, Issue 2953, pp. 123-124.
Iwabuchi, T (1967) General sweating on the hairy skin of the dog and its mechanisms. J Invest Dermatol. Jul;49(1):61-70.
Scott DW, Miller WH, Griffin CE. 2001. Muller and Kirk’s small animal dermatology, 6th ed Philadelphia (PA): WB Saunders
Carrier CA, Seeman JL, Hoffmann G. Hyperhidrosis in naïve purpose-bred beagle dogs (Canis familiaris) (2011) J Am Assoc Lab Anim Sci. 50(3):396–400.
