Getting a tan down on the beach is the goal of many during summer, but that bronzed body may come at a cost. Tanning, far from being some sort of benign summer magic, is the body’s reaction to damage caused by ultraviolet radiation (UV). Too much of that damage can result in life-threatening cancers.

Sunscreen is one of our major defences against UV overexposure, but it is not foolproof. Deficiencies exist in its labelling, safety and performance, and care should be taken over both the product you choose and how you use it


There are two types of ultraviolet radiation you need to protect against:

  • UVA, which does not cause sunburn, but which causes the “indirect DNA damage” that leads to melanoma.
  • UVB, which causes the “direct DNA damage” that manifests as sunburn.

Both types of UV cause collagen damage, skin aging and the destruction of vitamin A in the skin.

How Sunscreen Works

Sunscreens usually work in one of two ways. They either physically block and reflect sunlight so that it cannot reach the skin (remember the zinc cream you used as a kid?). Or they absorb the UV rays so that they cannot damage the skin beneath.

Whichever way they work, they need to provide adequate protection from both UVA and UVB. To do this they must be chemically capable of the task and they must be used correctly.

Choose a sunscreen that either states it protects against both forms of UV, or describes itself as “broad spectrum”.

When and How Often to Apply Sunscreen

Apply sunscreen 15-30 minutes before exposure and reapply every two hours. Reapply also after periods of profuse sweating, swimming, toweling or any other activity which removes the sunscreen from the skin – even if you’re using a “waterproof” sunscreen.

How Much Sunscreen to Use

The SPF rating of sunscreens (more on this later) is based on using 2 mg of sunscreen per square centimetre of exposed skin. This means that the average adult in a swimming costume needs around 29 grams of sunscreen to cover the entire body, or about one third of a teaspoon to cover the face.

Sunscreen Effectiveness

The effectiveness of sunscreen, regardless of its intrinsic protective qualities, will depend on:

  • The quantity used. Some studies have shown that people commonly only apply less than half the amount needed to achieve the sunscreen’s stated SPF level.
  • The level of UV exposure. UV levels are influenced by:
    • Ozone levels. Low ozone levels allow greater amounts of UVB to reach the surface of the planet.
    • Time of Day. UVB levels are highest at noon as the sun’s rays, striking the earth from directly overhead, have less atmosphere to travel through.
    • Latitude. The sun is most directly overhead at the equator, so UV levels here will be higher. In addition, ozone is naturally thinner at these latitudes.
    • Altitude. The higher you go, the greater the levels of UV. This is due to the fact that air thins with altitude and cannot absorb so much ultraviolet radiation.
    • Reflection. Snow, sand and water reflect UV radiation, bouncing it back at you and increasing your exposure.
    • Time of year. UV intensity is usually highest during summer months due to the changing angle of the earth in relation to the sun.

SPF – A Deceptive Protection Rating

Ever bought a sunscreen with a high SPF (Sun Protection Factor) and thought you were providing yourself with adequate protection from the sun? Think again.

SPF is a measure of how much UV radiation it takes to cause sunburn on protected skin as opposed to that required to cause sunburn on unprotected skin. But here’s the catch – it only refers to UVB radiation.

UVA – The Hidden Killer

The SPF rating system makes no reference at all to the potentially deadly UVA rays. So, theoretically, you can buy an SPF 45 sunscreen and, while you may avoid the sunburn-causing UVB rays, still be bombarded with melanoma-linked UVA.

In practice, some sunscreens using the SPF rating system do also contain ingredients which protect against UVA (sometimes described as “broad spectrum” sunscreens). The actual level of UVA protection offered by these sunscreens, though, has been questioned with the result that some manufacturers in some countries have adopted UVA protection rating systems alongside the SPF system.

Examples of UVA rating systems include the Japanese Persistent Pigment Darkening (PPD) system (used by manufacturers such as L’Oreal), and the Boots star rating system used in the UK. Sadly, in New Zealand, a country with high levels of UV radiation due to poor ozone protection, no mandatory UVA protection rating system exists.

If you’re concerned about UVA protection, look for sunscreens which contain zinc oxide, avobenzone, and ecamsule.

Sunscreen Safety

And, as if the lack of certainty around UVA protection wasn’t enough, the safety of sunscreen itself has been called into question.

Certain studies have suggested that the chemicals in sunscreen, if they can penetrate the stratum corneum (the outer “dead’ layer of the skin), could cause the formation of the free radicals and reactive oxygen species that have been linked with melanoma formation. Whether or not there is significant penetration of the stratum corneum remains open to debate.

The Best Protection We Have

Despite questions around UVA protection and stratum corneum penetration, sunscreen remains the recommended approach to bare-skin UV protection the world over.

So, whether you’re on the beach or schussing down the ski slopes, protect yourself from skin damage and melanoma before it’s too late. Slap on that sunscreen!

Learn more about the dangers of sunscreens here:

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