What you should know when buying sunscreen

Ever picked up a bottle of sunscreen and understood all the descriptors on the front? Us neither. With New Zealand having one of the highest incidence rates of Melanoma in the world, we thought it's high time we did.

What's SPF?

Your bottle's SPF (Sun Protection Factor) measures how well it protects the skin from sunburn. Standards New Zealand recommends you opt for an SPF 50+ (or higher), and to re-apply every two hours (regardless of what your bottle says, as that number will be tested under lab - not life - conditions). It's wise to adhere to their decision as you can burn in as little as 15 minutes (!) during the harsh New Zealand summer.

The SPF is probably the first thing you look at when you buy a bottle, but what else should you be looking for?

Is it water resistant?

Buying a water-resistant sunscreen means you're better protected when swimming, exercising or sweating. The word 'resistant' is important to note here - it's not saying 'waterproof', so these sunscreens will also need to be re-applied every two hours in order to stay effective.

Is it 'broad spectrum'?

This term may sound particularly vague, but it just means that the sunscreen in question is protecting you from both UVA and UVB rays. "Sunscreens exist to reduce UV-related skin damage," says dermatologist Dr Adam Sheridan.

"UVB and UVA both contribute to skin ageing and skin cancer, including melanoma. 'Broad spectrum' means both UVA and UVB are blocked, and both are important," he adds.

Should you choose chemical or physical sunscreen?

Otherwise known as 'absorbers' and 'scatterers'. Heather Walker, Chair of Cancer Council Australia's National Skin Cancer Committee, explains that these terms describe the way the sunscreen is working to protect your skin.

The 'absorbers' absorb the UV, and the 'scatterers' scatter it."

If you find a formula that you like, it doesn't really matter how it's protecting you, she says. And some sunscreen formulas contain both types of ingredients. "My advice is to try a lot of different formulas and find one you like, because you'll be more likely to wear it."

Should you buy a cream or a spray?

"Cancer Council doesn't recommend using aerosol sunscreen as it's so much harderto apply it correctly," says Heather. You need to deliver at least a teaspoon for everylimb, front and back of torso and face, neck and ears. That's a total of 7 teaspoons for a full body application - and much easier to do with a lotion or a gel.

Do you like it?

This may seem fickle, but your chosen sunscreen's accompanying factors - its smell, consistency, the way it sits on your skin - are all factors that will influence your readiness to apply your sunscreen in the first place.

I think I'm set. What else do I need to know?

Vitamin factor Studies have shown that using sunscreen doesn't stop you from topping up on vitamin D - so don't hesitate to apply it.

"In terms of vitamin D," explains Heather, "You really don't need very long outside to get your levels up. And the body doesn't store vitamin D - it just breaks down any excess - so overexposing yourself to UV will just increase your risk of skin cancer, without actually helping your vitamin D status.

"Our advice in general is to speak to your GP about whether supplementation is appropriate if you are deficient in vitamin D."

Are you in date? If, as the weather gets warmer, you're taking a fresh look at your sunscreen stash, then it's worth checking that it's in date, says Heather. "That can catch you out if you've had a big bottle of sunscreen in the cupboard for a while.

"They can go out of date, and that reduces their effectiveness. Plus, if they're stored in a place that's too warm, then over time they can separate, so check that it's the right consistency, that it looks how it should look and that it's in date."

And when it comes to wearing it?

"The way to find out whether you need sun protection is to check the UV." If it's at three or above, you'll need to be wearing sunscreen.

"It's a common misconception that the heat from the sun causes cancer, because you can often feel the heat from the sun and you can't feel or see the real culprit UV," she explains.

You can do this by checking the UV index on the National Institute of Water and Atmosphere website, or you can download the UV Lens app to find the current UV rating wherever you are.