User’s guide TO THE beach

SUNSCREEN 101: WHAT YOU REALLY NEED TO KNOW

Catching some rays sure isn’t as easy as it used to be. The world of sun protection involves a dizzying array of products, ingredients and SPF ratings. Sunscreen now comes in sticks, lotions, sprays and powders. There are so many choices that it’s easy to get lost wandering through the sunscreen aisle on your way to the beach.

Crunching the numbers on SPF: SPF, or sun protective factor, indicates how long a sunscreen increases the time before your skin burns. So if it usually takes 5 minutes before you turn pink, an SPF 15 sunscreen gives you 5×15 minutes or an extra 75 minutes before you burn.

The American Academy of Dermatology advises going with an SPF of at least 30, which should block out about 97 percent of the sun’s rays. If you have very fair skin, you should go even higher. In fact, some doctors believe a higher SPF is better because hardly anyone uses enough sunscreen. If you are using the same bottle all summer, you are doing it wrong.

If you are not slathering on a shot glass worth of lotion on your body, you are not going to get the benefit of the SPF on the bottle. Most people only use a quarter or half the recommended amount of sunscreen. If you stick with a high SPF you can work around some of that user error. And remember that two hours go by faster than you think. When in doubt, reapply.

That’s a wrap: Apologies to beach bunnies, but there is no sunscreen out there that can compete with simply covering up. And we don’t just mean a hat and some shades.

“The best sun-protective regimen is to wear sun-protective clothing, such as a rashguard, and also use sunscreen,” says Dr. Ngoc Pham, dermatology and medical director at Kaiser Permanente Santa Clara.

Check the expiration date: Sunscreens go bad by their listed expiration date unless they have been exposed to “extreme temperatures,” according to the Centers for Disease Control and Prevention. If a sunscreen does not have an expiration date and has been stored at room temperature — which does not mean sitting in your car in the heat of the summer — it has a shelf life of about three years. If you have a bunch of leftover sunscreen, it probably means you didn’t use enough last summer.

Secluded Gray Whale Cove State Beach, north of Montara, is reachable via a long staircase that leads down to the sands.

Alameda’s Robert W. Crown Memorial State Beach is popular with windsurfers and kiteboarders, too. A visitors center at Crab Cove includes an aquarium, tide pools and exhibits.