Think you're free of sun damage as long as you're wearing SPF? Think again. Here' what you need to know about choosing the right sunscreen and applying it effectively.

Most of us assume that, as long as we take the step of slathering on some sunscreen, we're covered—shielded from burns, melanoma, sun spots and wrinkles. In fact, there are many mistakes we make when choosing or applying sunscreen that can mean we get way less protection than we think. That's a big problem, especially considering that each of us has a one in six chance of developing skin cancer in our lifetime. Dermatologist Dr. Sonya Cook clears up some of our most common misconceptions that can lead to serious sunscreen mistakes.

Mistake #1: You think sunscreen is your best defence against sun damage.
"Sunscreen should really be the last line of defence," says Dr. Cook. In other words, we should prioritize things like wearing sun-protective clothing, staying in the shade and remaining inside mid-day when the sun is at its strongest. Of course, these protective measures aren't always possible, so sunscreen will help us avoid damage when we can't help but be exposed to the rays. Dr. Cook says it's never healthy to just lie in the sun—even if you're wearing a strong sunscreen.

Mistake #2: You choose your sunscreen solely based on the SPF.
"SPF is a measure of UVB protection only," says Dr. Cook. That means a sunscreen that has a super high SPF could potentially offer basically no protection against UVAs, which are the rays that penetrate deeper into the skin and are associated with wrinkling and pigment changes. The UVB rays are the ones that cause your skin to burn, and both types of rays can contribute to your risk of skin cancer. For protection against both UVAs and UVBs, look for the words "broad spectrum" on the bottle, and aim for an SPF of 30 to 60. 

Mistake #3: You don't apply enough sunscreen to get the SPF listed on the bottle.
"We know that most people don't apply adequate amounts of sunscreen and so generally are not getting as much protection as they believe," says Dr. Cook. The difference that underapplying makes is dramatic. Dr. Cook says that research has shown applying one-quarter of the proper amount of SPF 60 sunscreen results in protection that's comparable to SPF 3. So how much do you need? At least two tablespoons (about a shot glass full) if you're covering your whole body. "Get out the measuring spoons and become familiar with what two tablespoons of sunscreen looks like—and feels like when you apply it," says Dr. Cook. And don't forget to reapply every two hours that you're in the sun.

Mistake #4: You believe all forms of sunscreen are equally protective.
While it's true that spray, stick and lotion sunscreens might all be tested in a lab and given similar SPF status, in practice, some of the methods are harder to use properly. "It is very difficult to gauge how much you have applied with spray sunscreens," says Dr. Cook. "I generally recommend application of a lotion as a first layer and then reapplication with a spray if that is more convenient."

Mistake #5: You only use sunscreen in the summer or when you're at the beach.
While it's true that you're unlikely to get a sunburn in January, that doesn't mean you should ditch your sunscreen for more than half the year. Though UVB rays are much less intense in winter months, Dr. Cook says that UVA exposure—a contributor to skin cancer and aging of the skin—is fairly consistent year round. She applies sunscreen to exposed skin (like her face and hands) throughout the year and insists we all need to make it part of our daily routine.

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