Applying sunscreen when outdoors is a crucial measure to help avoid sunburn, reduce your long-term risk of skin cancer, and minimise premature skin ageing.   However, it can be difficult to choose a sunscreen when presented with the huge variety of choices available in the shops.  This article gives a brief overview on some of the key things to look out for in your sunscreen.


SPF stands for Sun Protection Factor.  It tells you how much longer it takes to burn the skin compared to not having any sunscreen on at all.  As a simple rule, the higher the SPF, the greater the sun protection.  A sunscreen with SPF15 will give 15x the protection of not having any sunscreen on.  This means that in conditions that would start to burn the skin in 10 minutes, SPF15 would increase this time to 150 minutes.  With SPF30, it would take 300 minutes and so on.  Now, this figure assumes that the person continues to top up the sunscreen every 2 hours and has applied a generous amount of sunscreen (at least 6 teaspoons full per average sized adult).

UVA and UVB:

When UV light passes through the ozone and lands on your skin there are two types of UV rays: UVA and UVB.  UVB tends to hit the surface of the skin and is the main culprit for causing sunburn in the short-term and skin cancer in the long-term.  UVA rays penetrate deeper in the skin and are the main cause for premature skin ageing, but can also contribute to sunburn and skin cancer.  

With SPF being determined by the time to burn, it is clear that this is mainly a measure of how good a sunscreen is at blocking UVB rays.  Currently there is no consistent way for manufacturers of sunscreen to report on how effective the sunscreen is at blocking UVA rays.  However, those that say they block UVA and UVB, or that they are ‘broad-spectrum’ have to provide protection against UVA that is at least 30% of the protection given against UVB.

What about the ratings?

Consumer NZ provides real-life testing of sunscreens to see whether they meet their SPF and broad-spectrum claims.   This gives you an excellent starting point when choosing your sunscreen, but shouldn’t make you panic if your existing sunscreen appears to fail their tests (in most cases).

This is because, no sunscreen blocks 100% of UV-rays.  On the most recent Consumer NZ report, the lowest ‘real-life’ SPF for a sunscreen that didn’t meet its reported SPF was 29.2.  Although this is a big discrepancy, it’s important to consider that SPF15 blocks around 93% of UV rays, SPF30 97% and SPF50 98%.  So the real drop in protection is only 1% with this SPF50 sunscreen that failed to meet its reported SPF.

That being said, this drop in SPF between what the bottle says and what the sunscreen provides in real-life does become much more important when thinking about UVA ray protection.  With this only having to be a third of the protection given to UVB, this can start putting your skin at real risk.

So, what should you do?

  • With the high UV levels seen in New Zealand, I would always recommend SPF50+ sunscreen.  This will give excellent UVB protection whilst providing a good level of UVA protection.
  • Apply sunscreen whenever outside and UV level is above 3.  There are lots of Apps available that tell you the UV for the day (I use uv2day).  To minimise premature skin ageing, I would recommend applying sunscreen everyday of the year
  • When picking which sunscreen to use, keep an eye on the Consumer NZ website to monitor which sunscreens seem to be failing to meet their reported SPF protection.  
  • Avoid aerosol-based sunscreens, as most people fail to apply anywhere near enough spray on lotion to meet the manufacturer’s guidelines that are needed to achieve the reported SPF.
  • Re-apply every 2 hours and after being in the water (especially if you towel dry yourself)
  • Finally, sunscreen is just one measure to protect your skin from the sun.  Combine this with a wide-brimmed hat, UV protecting sunglasses, UV protecting clothes and avoiding being out in the sun during the middle of the day.

Go and have fun in the sun, but I hope this information helps you stay safe at the same time!