KANSAS CITY, Mo. - Here's a heated debate: Is the summer sun more good or more bad?

For the sun-sensitive, the sun is one big, flaming irritant - too hot, too bright, too much. But for sun worshippers, old Sol represents fun, freedom, happiness.

So who's right? As the warm and wonderful days of summer - or is that the dangerous and uncomfortable days of summer? - approach, let's start filling out the balance sheet on this burning hot question.

We'll start with the bad.

The sun can kill you. An estimated 200 people die every year in this country from heat-related illnesses, according to the National Institute of Aging. Many shut-ins who lack air conditioning or fans die from heat stroke, a condition in which the body temperature gets so hot victims cease to sweat, and their internal organs shut down.

Extreme exposure to the sun also has helped (in the absence of water) kill people stranded in the middle of deserts.

Given enough extreme exposure the sun's damaging rays can lead to melanoma that, left untreated, also can be fatal. An estimated 116,000 new cases of melanoma will develop in 2008 in the United States, according to the American Academy of Dermatology.

More than 8,400 are expected to die of melanoma, with 2,500 more expected to die of squamous cell skin cancer.

But the sun is 93 million miles away. How can it kill from that distance?

Two words: nuclear reactions.

"The sun is very, very powerful," said University of Kansas professor of physics and astronomy Barbara Anthony-Twarog. "There are nuclear reactions happening many, many times per second in the center of the sun."

And during the summer months, when the Earth points toward the sun, we're essentially standing directly in front of the furnace.

The sun can damage your skin. Too much summer sun can not only give you a painful sunburn and cause your skin to blister and peel, but over the years it also can leave it leathery and wrinkled, causing you to look older.

How, exactly, does the sun damage your skin?

Blame ultraviolet light, said Daniel Aires, division director of dermatology at the University of Kansas Medical Center. Too many damaging rays can cause cells to mutate by altering your skin's DNA.

After a sunburn, your skin cells change. They can even die. That's when your immune system goes to work to protect you. It increases blood flow to the affected area, causing your skin to get red and warm. The blood brings white blood cells that help clean up the bad cells. The top layer of your skin then peels off and is replaced by a new layer.

Over the years the damage can build up. Scientists have shown a link between repeated severe sunburns and potentially deadly melanoma.

With prolonged sun exposure on unprotected skin, the sun's UV radiation can penetrate past the epidermis - the top layer of skin - to the dermis layer below. It can also cause the elastin in your skin - the stuff that makes baby skin so soft and smooth - to break down.

The result: dry, leathery, alligator skin.

"As a dermatologist we do full skin exams," Aires said. "And let me tell you, we have some patients lying on the table with faces in their 70s who have butts in their 40s. That's the sun."

You can protect yourself by limiting your exposure to the worst burning rays (between 10 a.m. and 2 p.m.), and by using - and consistently reapplying - sunscreen, or by wearing hats and gloves.

3. The sun can make you sweat. OK, but to be fair, so can indoor exercise. But, sure, stay out in the sun too long and you're going to sweat. Just keep in mind that there's a good reason for it.

When your body temperature rises, millions of sweat glands secrete a fluid onto the surface of your skin that cools your body as it evaporates. So that's not really the sun's fault. It's just the body's reaction to getting hot - sun or no sun.

4. The sun can give some people a headache. Yes, but so can coughing, sneezing, lifting weights or certain smells. Not sure that one can be blamed on the sun.

5. The sun can harm your eyes. Too much sunlight on unprotected eyes can damage your retina, increasing the chances for macular degeneration (a kind of vision loss) as you age. To protect the light-sensing cells at the back of your eye, doctors recommend wearing sunglasses with amber or green tinted lenses. They filter out most of the sun's harmful radiation.

6. The sun costs you money. Air conditioners. Sunglasses. Sunblock ... .D'oh! (Or is that dough?)

7. The sun fades your possessions. Whether it's drapes, upholstery, siding, your car, even your wood furniture or valuable pictures, constant exposure to the sun will damage them.

And now for the good. (We don't have room for all the benefits of the sun. But here are a few.)

1. The sun makes photosynthesis possible. We may not think much about this natural process, but it's sort of important if we want to - how should we put this? - keep on living.

Simply put, it's the process by which plants convert light energy into useful things such as oxygen.

2. The sun gives us vitamin D. Moderate exposure to sunlight will kick off the chemical and metabolic chain reaction that produces vitamin D, which is important for your body. Some research now shows many people have low vitamin D levels, and not everybody can afford daily vitamin D supplements. There is a well-documented relationship between low vitamin D levels and poor bone health. But that's far from all it does.

"Ninety percent of the genes that respond to vitamin D have nothing to do with calcium and bones," Aires said. "These are thought to be some of the ones important in cancer and immune diseases."

Recently links have been made between low vitamin D levels and maladies ranging from multiple sclerosis to prostate cancer. ("Linking" low vitamin D with these diseases doesn't prove cause-and-effect, but it suggests at least some relationship.)

3. The sun can help chase away the blues. Research shows that light hitting your skin can help reverse seasonal affective disorder, sometimes called the wintertime blues.

4. The sun helps food grow. Kind of a big one.

5. The sun makes summertime activities possible. You like to swim, boat, fish, golf, etc? Thank you, sun.

6. And finally, try living without the sun. Without the sun the Earth would cool, the plants would stop growing, the oceans would freeze, the animals would die, and we wouldn't be far behind.

That's it. We're calling it. Game, set and match to the sun as more good than bad.

Just be careful out there. Even too much of a good thing can be bad.

As Aires, the dermatologist, said: "I'm pro sun. I just think people need to be sun-smart."

_