Summer survival guide.

Keeping your cool can be a real challenge during the dog days of summer. And not just for humans. Animals have to adapt to hot weather too. Many critters use the same methods humans do. To check out our common heat-survival techniques, read on.

NO SWEAT

As the mercury rises to 90[degrees]F (32.2[degrees]C), people and other animals are sweating up a storm. At least those with sweat glands, glands beneath the skin that secrete water and tiny amounts of minerals. Like humans, these animals (primates, pigs, and horses) perspire to stay cool, says Ed Spevak, assistant curator at the Bronx Zoo/Wildlife Conservation Park in New York.

When your body temperature rises, the tiny muscles surrounding your body's 3 million sweat glands contract. The contractions squeeze perspiration (which is 99 percent water) through pores onto the skin's surface. When the sweat evaporates, it removes heat from your body, cooling you down.

But how do animals that don't sweat keep their cool? They evaporate water too, says Spevak, "but they do it in different ways."

Some critters--like cats, dogs, and birds--pant, or breathe in air quickly, says Spevak. Panting helps evaporate water in the animal's mouth, which cools the airways and helps bring down body temperatures, he explains.

Other animals that can't sweat flap. Birds flap their wings, while elephants flap their giant ears, which contain many blood vessels. Flapping helps transfer heat from blood to the air to cool the whole animal, says Spevak. Flapping doesn't work as well for you because no part of your body has that many blood vessels, close to the surface of your skin.

Body-cooling adaptations help keep animals functioning properly. But you can get "too much" of a good thing. Lots of sweating, for example, can lead to dehydration--the depletion of body fluids. That's why filling up with water--especially in the summer--is important.

The amount of water an animal needs depends on its size and level of exertion, says the Bronx Zoo's veterinarian Dr. Robert Cook. Humans need at least 2.8 liters a day. Exerting yourself increases your body's demand for water even more. An exercising human can lose up to 11.4 liters of fluid a day.

When you sweat that much, you also lose minerals like potassium and sodium, says Bill Fink, an exercise physiologist at Ball State University in Indiana. Sodium helps maintain the water balance in your cells. And both sodium and potassium keep your muscles and nerves functioning properly. Manufacturers of "sports drinks" claim their products can replace lost fluids and minerals. But you can achieve the same balance, says Fink, by drinking water and eating a balanced diet.

Manufacturers also claim that sports drinks boost your energy level. That's because they contain energy-rich carbohydrates. Sports drinks do benefit "serious athletes like marathon runners--or those who exercise strenuously for at least an hour and a half [at a time]," says Fink. These athletes lose excessive amounts of fluid and minerals. But for the average person, Fink says, quenching your thirst by drinking water is just as good.

So gulp a few liters every day. And leave plenty of clean, fresh water for your pets.

SKIN BAKE

Though liquids can help hydrate tissues and cells, they don't do anything for sun-parched skin. Most animals keep their skin from becoming scorched by staying out of the sun, says the Bronx Zoo's Ed Spevak. That's a good natural instinct because, like humans, other animals can get sunburned--and even develop skin cancer.

The damage is caused by the sun's dangerous ultraviolet (UV) rays. When UV rays pass through the skin, they penetrate the skin's pigment cells, known as melanocytes, says Dr. Seth Orlow, director of pediatric dermatology at New York University Medical Center. The melanocytes divide rapidly and produce more melanin, or pigment, which makes you tan.

You may think a tan is cool, but it's really a sign that UV rays are damaging your skin, says Dr. Orlow. For one thing, UV rays weaken the elastin and collagen protein fibers that keep your skin smooth. They also penetrate your skin cells' DNA, the genetic blueprint that controls all cell functions. Absorption of these rays can lead to a mutation, an error in your genetic blueprint.

Changing the genetic material in the skin increases the risk of skin cancer, rapid growth of abnormal cells, says Dr. Orlow. According to the American Cancer Society, an estimated 34,100 Americans will develop melanoma, a deadly form of skin cancer, this year. Overexposure to sunlight in your teenage years can put you at risk. Other forms of skin cancer can result from lower levels of exposure.

So it's important to protect yourself by applying sunscreen or sunblock, says Dr. Orlow. Sunscreens contain chemicals that absorb UV rays before they penetrate the skin. Sunblocks, like titanium dioxide and zinc oxide, "block" UV rays completely by reflecting them away from the skin.

Slather on lots of sunscreen or sunblock with a sun protection factor (SPF) of 15 or higher (see "Sunscreen screen test," left). And remember that sweating or swimming will wash away the sunscreen, so reapply often. You can protect your pets with sunscreen too, says Dr. Glenna Mauldin of the Animal Medical Center in New York City. There's no sunscreen made especially for pets, says Dr. Mauldin, but you can use a brand made for humans. Apply sunscreen to the animal's nose and ears--where most animals have less fur.

Some animals create their own sunscreen. A hippopotamus, for example, excretes a red-pigmented slime onto its skin, says the Bronx Zoo's Ed Spevak. The ooze hardens and prevents the sun's damaging rays from penetrating. Elephants, rhinos, and water buffalo use another technique: They cover themselves with a protective layer of mud.

FASHION STATEMENTS

If you're like most people, you probably prefer cleaner coverups. Dr. Orlow recommends wearing lightweight cotton long-sleeve shirts and pants, and a widebrim hat or cap. (And don't forget sunglasses to protect your eyes! Light-color clothes will also reflect sunlight away from your body, so you feel cool.

Now if anyone asks you how to beat the dog days of summer, you can tell them to chill out with SW's summer survival guide.