It feels almost like a betrayal, a complete absence of harmony with the ecosystem, to accept that the sun is in some ways harmful to humans.

But it is. My eye doctor recently told me I need sunglasses to retard the cataracts I now have growing. Dermatologists also tell us we need gooey sunscreen to prevent skin cancer.

And now, to top everything, health advocates say many of those lotions and sprays don't work as well as we think, and some might even be harmful.

We have to pay attention. In February, NASA scientists analyzing 30 years of satellite data measured just how much the UV radiation reaching the Earth's surface had increased, largely due to decreased stratospheric ozone.

At Washington, D.C.'s latitude, it increased 9 percent since 1979. The good news is that they also concluded the trend might be leveling off, the result of countries' limiting the emission of ozone-depleting gases such as some refrigerants.

On Friday, timed to the start of the summer beach season, the U.S. Environmental Protection Agency declared it a "Don't Fry Day," reminding people that the number-one preventable risk factor for skin cancer is to avoid overexposure to UV radiation. (They even have UV Index apps for smart phones.)

But sunscreen is no panacea. Typically, we underapply it, or don't reapply it after swimming, or use it as an excuse to stay out in the sun too long so we burn anyway.

In a study published in November in the journal Cancer Research, scientists found that nanoparticles of titanium dioxide, a common sunscreen ingredient, caused genetic damage in mice that typically raises the risk of cancer.

But the researchers said the nanoparticles cannot go through skin, so they recommended lotion sunscreens rather than spray-ons, which can be inhaled. Above all, don't let your kid eat it.

Last week, the Environmental Working Group issued its annual sunscreen guide. The national nonprofit is skeptical of industry and focused on the "body burden" of chemicals such as bisphenol A.

Analyzing more than 500 products, its researchers concluded they could recommend only 39, or 8 percent.

They liked sunscreens with zinc and titanium (although, again, don't inhale it or eat it). They're the ones that are kind of whitish, which may not go over so well with anyone but lifeguards, who can get away with white noses.

They provide a literal block, scattering the UV rays, as opposed to other sunscreens that have complex molecules that actually absorb the UV rays. The group recommended brands by Miessence, Kabana Skin Care, Badger, and All Terrain, among others.

What the EWG didn't like were sunscreens containing oxybenzone, which it said is a hormone-disrupting compound that penetrates the skin and enters the bloodstream.

They also have new worries about a Vitamin A compound in about 40 percent of sunscreens, retinyl palmitate, which may be "photocarcinogenic," which means sunlight may cause it to undergo complex biochemical changes. It has been linked to accelerated growth of skin tumors and lesions in lab mice. They said that while the research is inconclusive, why take a chance?

The EWG is pressing the Food and Drug Administration to finish its research on the compound, not to mention complete the sunscreen regulations it started in 1978.

The organization also is concerned about SPF, sun protection factors, of more than 50, which often come with "exaggerated" claims of protection. Plus, higher-SPF formulations contain greater concentrations of the sun-blocking chemicals that may be harmful.

The group's report, including an online query to check on specific products, is at www.ewg.org.

As incredible as it may seem, sunscreen may even be bad for other creatures on the planet.

Italian researchers looked at their effects on corals. Their peer-reviewed study, in a 2008 issue of Environmental Health Perspectives, found that even at low concentrations in seawater, sunscreens cause viral infections that can kill the coral.

To be sure, sunlight has benefits. The Vitamin D we get from it maintains our calcium levels, benefits the immune system, eases depression, and more.

Plus, it plain old feels good. When I was a kid visiting my grandmother at the Jersey Shore, nothing felt better than staying in the ocean until my mother insisted I get out because "you're so cold your lips are blue," and then flopping on a beach towel to let the sun dry and warm me.

But in the end, as long as we have to limit exposure, perhaps the advice of our grandmothers is the best: Wear long sleeves and a hat.

Contact staff writer Sandy Bauers at 215-854-5147 or sbauers@phillynews.com. Visit her blog at http://go.philly.com/greenspace.