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Sunscreen is a hotly debated subject - from physical to chemical screens, broad spectrum to what those numbers on the bottles really mean. Editor Trudi Brewer sheds light on the number one anti-ageing beauty product you must wear daily an SPF.

Top sunscreen tips

There are many myths and facts around sunscreens, mostly around numbers and what SPF 15, 30 and 50 offer. The number is an indication of the protection you will receive during peak burn time in New Zealand, that's between 11-2pm. In this country it's around three minutes, so, in short, an SPF 30 x 3 = offers around 90 minutes of protection, before you need to reapply. While an SPF 50 x 3 = offers around 150 minutes. However, no SPF offers 100 percent protection. In fact the higher the number, the very little difference in protection. For example, an SPF30 filters 96.7 percent of UV radiation, while an SPF50+ filters 98 percent of UV rays. 

How much should you apply to get that SPF rating of protection? Well, no one uses the recommended amount (that is what is tested in a lab on human skin, which is 2mg of sunscreen every per square centimetre of skin) or one teaspoon full, for each limb. You should be applying a generous amount of sunscreen (enough to see it on your skin) and layer it on 15 to 20 minutes before you step outside, and then reapply every hour. Remember this is a guide, and don't forget those hard to reach spots including, neck, ears, back of knees and the scalp.

An SPF in your makeup is not enough protection for your face. The New Zealand Cancer Society recommends an SPF 30 as the standard in sun protection. I always layer on sunscreen. Using an SPF 30 moisturiser, underneath an SPF15 makeup, followed by a dusting of mineral powder for extra protection. Also, those of us sitting in an office still need a sunscreen. The most recent threat to our complexion is HEV or blue electromagnetic rays, (emitted from your phones, computers, laptops, microwaves, and  tablets). These don't burn the skin, but they pump out UVA (ageing rays) so they will age the skin over time.

The most significant debate is chemical vs. physical screens when it comes to SPF. And who suits what. My preference is physical sunscreen - these are organic mineral ingredients that suit my skin, however it is a matter of trial and error. Most dermatologists will recommend a sunscreen that offers both physical and chemical sunscreen. A quick tip: Chemical screens absorb and destroy UV rays before they can damage skin - these are often listed as oxybenzone and avobenzone on the label. While physical screens, block the suns rays, putting a barrier between your skin and the sun. These are listed as titanium dioxide and zinc oxide on the label. A mix of both, blocks and mops up any excess UV radiation that can damage your complexion.

Always look for the words 'Broad Spectrum' on the label. This guarantees you are protected from the UVA rays (ageing rays can penetrate clouds and windows) and UVB rays (burning rays cause long-term damage and skin cancer).

For anyone with sensitive or acne-prone skin, opt for a fragrance-free and paraben free SPF. And opt for a physical screen (zinc oxide or titanium dioxide), rather than a chemical screen (oxybenzone or avobenzone). These are better for anyone with sensitive skin or prone to break out, as the ingredients are organic and earth-derived and are less likely to cause reactions or clog pores. 

Always use a different face and body sunscreen. Facial sunscreens are matte (less greasy and contain tinted minerals) while body sunscreens are designed to cover a larger area, so they are thicker and more opaque in colour. And check the expiry dates, these matter. If your SPF has expired it will not work effectively.