Skin cancer is the number one cancer in the United States. Everybody knows that the number one cause of skin cancer is sun exposure: the highest rate of skin cancer in the world is among fair-skinned people of Scottish descent who live in Australia. However, not everybody knows what provides the best sun protection.

If you want to be outdoors, but you do not want skin cancer, try to avoid the sun between the hours of 10 and 2, especially in the summer. If you do go out during this time, wear sun-blocking clothes (Travelsmith and Solumbra have good products). You can make your own clothes into sun blockers by washing them in SunGuard (call 866-871-3157), which will last through 20 washings.

Things start to get tricky when you go to buy a sunscreen for your exposed body parts. Choosing a good sunscreen is not as simple as it appears. Some of the sunscreens with staggeringly high SPF ratings do not, in fact, give you adequate protection from skin cancer.

To understand why, you need to know that there are three types of skin cancer: basal cell (bad), squamous cell (worse) and malignant melanoma (truly terrible). You also need to know that sunlight contains two different kinds of cancer-causing rays: UVA and UVB.

UVB is the ray that causes you to burn (think: “B=burn�). It is also the ray that causes basal and squamous cancer.

UVA is the ray that causes you to tan, but at a price: it also causes your skin to age (think: “A=aging�). Worse, it is the ray that stimulates deadly melanomas.

UVA rays penetrate clouds. They penetrate glass: airline pilots have high rates of skin melanoma. They are the tanning agent in tanning salons: there is an epidemic of melanoma in young people who have patronized these salons.

The “SPF� factor in sunscreens only tells you how well this product protects you against UVB rays. It tells you zero about protection against UVA rays. In fact, there are only two ingredients that give you adequate protection against UVA rays: titanium dioxide and zinc oxide.

Go and get your tube of sun screen. Look at the label. If it does not say titanium dioxide and/or zinc oxide, throw it into your wastebasket. Go buy a sunscreen that does. CVS has a good sunscreen, and so does Trader Joe’s.

You will probably notice that sunscreens that contain these two vital ingredients tend to make your skin look somewhat white. Believe me, white skin is a small price to pay for protection against malignant melanoma.

Dr. MacKay Keegan, an ophthalmologist and longtime Brooklyn Heights resident, has contributed travel articles to this newspaper.

© Brooklyn Daily Eagle 2009 All materials posted on BrooklynEagle.com are protected by United States copyright law. Just a reminder, though -- It’s not considered polite to paste the entire story on your blog. Most blogs post a summary or the first paragraph,( 40 words) then post a link to the rest of the story. That helps increase click-throughs for everyone, and minimizes copyright issues. So please keep posting, but not the entire article. arturc at att.net