Putting on sunscreen is becoming a key part of many Canadians' daily ritual, as summery weather returns. Dr. Cherly Rosen, head of dermatology at the University Health Network, answers some key questions about sunscreen and sun protection for CTV's Canada AM.

Q: What's the difference between different SPF levels (ex: SPF 15, SPF 30, SPF 60)?

A: They're all protective, but SPF 30 or higher protects against sunburn, Rosen says. SPF 30 or higher also protects against other effects of sunlight like damaging DNA and causing skin cancer, she says.

However, because people put on less sunscreen than is used in testing, it's often good to use a higher number SPF, Rosen says. This is because you wind up with a lower degree of protection because you haven't put on as much as is used in tests.

Q: What's the difference between sunscreens that protect against UVA and UVB?

A: SPF primarily protects against ultraviolet B rays, as UVB is far more capable to cause sunburn than ultraviolet A. But UVA also causes damage to the skin and is implicated in skin cancer, Rosen says.

Look for a sunscreen that protects against both UVA and UVB, she says, noting that sunscreens that use the word "broadspectrum" protect against both kinds of ultraviolet rays.

Q: Is it true that once you're using SPF 30 there is no more benefit in going with a sunscreen with a higher SPF?

A: That's not true. SPF tells you about protection against sunburn, but there are other endpoints to consider besides sunburn, such as cancer prevention, preventing skin damage, and preventing wrinkles, Rosen says. It's worth using a higher number SPF if desired, because we don't really know the optimal value for protecting against those endpoints, she says.

Q: Should people be concerned about the chemicals contained in sunscreen?

A: When you look at sunscreen on human skin, the risk is very minimal, if any, Rosen says. Sunscreens are made to stay on the surface of the skin, not to be absorbed by it.

The benefit to protecting your skin really outweighs the theoretical risks, Rosen says. "We really keep looking and haven't found actual risk to humans."