Here's some bitter irony for you: A key ingredient in many sunscreens can actually cause the very cancers they're supposed to prevent.

That's not even the most ironic part. Ready for it? This ingredient only becomes dangerous when exposed to the sun.

Ouch! Sunburn is looking better all the time.

The ingredient is vitamin A, which is usually harmless enough if you get it the right way--from spinach, carrots or a good supplement. You need it for everything from your eyes to your immune system.

But you definitely don't need it in your sunscreen or skin cream, because studies have shown that this stuff can actually give a turbo boost to cancer cells when exposed to UV light.

And as you probably know, our top source of UV light is the sun.

Now, the skincare industry's dirtiest secret has been exposed to the light-- because a key scientific advisory panel has just signed off on the draft assessment from the National Toxicology Program that confirmed the link after a series of animal tests.

And that means it's time to get this stuff out of your home--and definitely out of your beach bag.

Here's what you need to do: Check the labels on any skincare products you have and look for "retinyl palmitate." That's the vitamin A, and it's currently in some 200 sunscreens from major manufacturers--including Coppertone, Banana Boat, and Neutrogena.

But let's make this even easier than searching the fine print for some funny words--because the truth is, you don't need sunscreen in the first place.

Despite what you may have heard, the sun is not your enemy and you don't need to slather on a chemical concoction every time you step outside.

Quite the opposite--because that approach has left us so badly deficient in vitamin D that most people now need a supplement just to get what they need.

But the cheapest "supplement" on the planet is right outside your door: Your body can make its own D with about 15 to 20 minutes of direct sunlight a day.

Getting the D you need will help your bones, brain, heart and immune system-- and unlike sunscreen, it may even help you avoid some cancers.

One new study on mice finds that low levels of D can actually stunt the growth of the lungs--leading to decreased volume and function, possibly setting the stage for asthma and other breathing problems.

I recently went into detail on how much D you need and how to get it. Click here to read it now. You can even print it out and bring it outside--just be sure to head back in before you turn into a lobster.