HOW COME? It's sweating dogs and cats

How come dogs only sweat on their noses? asks Tunisia Solomon. How do cats keep cool, if they don't sweat? asks a reader.

For us humans, it seems simple: Take a walk on a 90-degree day. Get sweaty. Retreat to an air-conditioned room. But what's a dog -- or a cat -- to do in the dog days of August?

Actually, both dogs and cats do sweat a little. But it's not enough to get rid of the heat generated by their working bodies.

Dogs, cats and humans all have two varieties of sweat glands, apocrine and eccrine. The bigger apocrines are located around hair follicles in places like armpits, chest and scalp in people. The fatty sweat that oozes out doesn't really cool us. Instead, it's part of our natural scent (aka body odor).

Eccrine glands are smaller, and number in the millions. Their main job is to keep us from overheating. Under orders from the temperature-regulating hypothalamus gland, eccrines secrete salt, attracting water from inside the body. As air evaporates our saltwater sweat, skin and blood vessels cool, helping keep our core temperature from soaring to dangerous levels.

Ever smelled a wet dog, one who hasn't had a bath in months? If so, you won't be surprised to learn that hairy mammals like dogs have many more apocrine glands than we do. Each animal's distinctive smell is important to its doggy social life. But the pungent sweat doesn't help in the heat.

Dogs also have eccrine glands. But instead of covering his body, a dog's far fewer eccrines are concentrated on his paw pads. There's also a smattering on a dog's nose.

While salty paw sweat creates better traction for a dog's feet, it's not enough for cooling. On a hot day, blood vessels in a dog's face and ears dilate, allowing more blood to pass near the surface, releasing heat into the air. A dog's built-in cooling fan is panting. When a dog pants, air moves across the moist, mucous membranes of his tongue, mouth and throat. As water evaporates from these surfaces, a dog's body cools.

Cats sweat through their paws, too. But as with dogs, it doesn't help much in the heat. So cats chill out on cool surfaces, like tile floors. They also take frequent baths, cleaning their fur with their tongues. By spreading saliva, cats coat themselves in water, which evaporates like our eccrine sweat.

A cat exposed to high temperatures will begin to pant. But unlike a dog, a panting cat is showing signs of stress. All pets should be given plenty of cool water, and a shady or air-conditioned place to rest in the heat.