This information is from an article in a recent edition of Parade Magazine. It'll help you make sure that sunscreen is giving you the protection you think it is.

1. You need sunscreen in the car.

Newer car windshields block out nearly all UV radiation, but you're still exposed to damaging UVA rays through the side and rear windows, especially if they're not tinted. And believe it or not, the same is true when you're sitting in the window seat of an airplane.

2. And don't forget about the winter time.

Although you're outside less, and bundled up while you are, your face and hands are still often exposed to harmful rays. And snow reflects up to 80% of the ultraviolet light that hits it, increasing your risk. Elevation also compounds the problem. For every 1,000 feet above sea level, ultraviolet exposure increases about 2%.

3. You probably need another coat.

“The general rule is a shot glass full for the whole body. But if you’re in a bathing suit, that may not be enough,” says dermatologist Cheryl Karcher.

4. SPF isn’t everything.

The number gauges how well a sunscreen fends off UVB light—but not UVA rays. To ensure your formula protects against both, scan the label for the words “broad spectrum” and more than one of the following ingredients: avobenzone (Parsol 1789), Mexoryl, titanium dioxide, or zinc oxide.

5. Sunscreen ­weakens when exposed to heat and light.

Store it in a cool place, not in the trunk of your car. Get formulas with stabilizing ingredients, like Helio­plex or Dermaplex.

6. You may need to wear it indoors.

Unless they’ve been specially treated, the windows of your home or office ­typically won’t shield you from damaging rays, says dermatologist Francesca Fusco.

7. And underneath your clothes.

The ­average white cotton T-shirt ­provides an SPF of 10 or less.

— Cara Birnbaum and other sources