Dialog Box

Skin Health Institute

Sunscreen Explained


SPF Applying Types Nano particles Sources

Sunscreens come in many different forms including sprays, lotions, broad spectrum and water resistant.

So how do you know which one is best for you?

SPF Explained

What does SPF mean?

Sunscreens are made of a mix of ingredients to help prevent the sun's ultraviolet (UV) radiation reaching your skin and come in a range of SPFs.

SPF stands for Sun Protection Factor and is a measure of a sunscreen's ability to prevent one type of UV radiation called UVB (think B for burning) from damaging the skin. UVB rays cause sunburn and several types of skin cancer.

Red skin is a reaction to UVB rays alone and tells you little about other UV damage you may have done.

Another type of radiation, UVA radiation, penetrates deeper into the skin and can cause premature wrinkling, age spots and also heighten the risk of some skin cancers.

Sunscreen lotions labelled broad-spectrum block against UVA and UVB, but currently there is no standard listing for UVA block power.

Some inorganic chemicals that are found in sunscreen, including zinc oxide or titanium dioxide act as a physical sunblock that deflect both UVA and UVB rays.  In the past, sunscreen showed up on the skin as a visible white layer however, sunscreen manufacturers now make the inorganic particles much smaller, so we don't see the visible white (see nano particles below).

SPF 15, 30 and 50

The Skin Health Institute recommends using a sunscreen with an SPF of 50+.

No sunscreen will block 100% of UV rays, which is why it is important not to spend prolonged periods of time in the sun, even whilst wearing sunscreen.

Because some UV radiation still gets through the sunscreen and into your skin, the SPF number refers to roughly how long it will take for a person's skin to turn red. 

Sunscreen with an SPF of 15 will prevent your skin from getting red for approximately 15 times longer than usual. If you start to burn in 10 minutes without any sun protection, sunscreen with SPF 15 will prevent you burning for about 150 minutes*.

If used correctly, SPF 15 sunscreen filters out approximately 93 per cent of UVB rays, SPF 30 filters out 97 per cent and SPF 50 keeps out 98 percent.

However, because most people don't use enough sunscreen and because sunscreen tends to wear or wash off after time, you should reapply an SPF 50+ sunscreen every two hours, regardless of its strength. 

The '+' sign

The plus sign means 'more than'. For example, SPF50+ sunscreen must provide at least SPF60 in testing. This is because the same batch of sunscreen will test slightly differently in different laboratories with different methodology. By testing at SPF60, it removes any margin for error.


How much sunscreen should I apply?

An average sized adult should apply the equivalent of one teaspoon of sunscreen to each arm, leg, front of the body, back of the body, and face (including the neck and ears). Most people apply less than half this amount, which means they get far less protection than the SPF stated on the bottle.

When should I apply the sunscreen?

Ideally, sunscreen should be applied about 20 minutes before being out in the sun, so it has time to absorb into the skin. Once you are out in the sun and are sunburnt then sunscreen will be useless.

Is sunscreen by itself enough?

Sunscreen should form part of overall sun protection that includes clothing, hats, seeking shade and avoiding being out in direct sunlight when it is brightest (SLIP on a shirt, SLOP on some sunscreen, SLAP on a hat, SEEK shade, SLIDE on sunglasses). 


Water resistance

Water resistance sunscreen means that it does not come off the skin during swimming or exercise, provided it is not wiped off. Some labels will state that the sunscreen is '4 hours water resistant' but you should still reapply sunscreen every 2 hours to maintain the same level of protection.


Without a broad-spectrum sunscreen

With broad-spectrum sunscreen

Broad-spectrum sunscreens filter both UVA and UVB rays. UVB is the principal cause of sunburn, but both UVA and UVB contribute to increased skin cancer risk. 

Learn more about how UVA and UVB damage your skin. 

Waterproof, sunblock, sweat proof

Revised Australian Standard on sunscreen means these words are no longer permitted on sunscreen labels.

The term 'waterproof' is misleading and not permitted. The Standard acknowledges that sunscreens will wash off when immersed in water.

The term 'sunblock' is misleading and not permitted because it may be interpreted to mean that 100% of the sunburning radiation is blocked. 

The term 'sweat proof' is misleading and not permitted. 'Sweat resistance' is not a substitute for 'water resistance'.**

Nano particles

For many years sunscreen manufacturers have used the inorganic compounds titanium dioxide and/or zinc oxide to deflect or filter UV rays.  In its bulk form, this would leave an opaque or white film on the skin, which resulted in consumers being reluctant to use them (although it's quite an Aussie thing to wear zinc cream on the nose). Since those early days, science has evolved to allow the manufacturer to decrease the size of these metal oxides to be nano particles.  When used in a sunscreen, they cannot be seen on the skin, and they have even enhanced the effectiveness of the sunscreen. The nano particles are also particularly effective in filtering UVA as well as UVB rays, thus providing very effective broader spectrum protection.

However, some have feared that these nano particles can penetrate the skin and get into the blood stream.  This has stimulated quite a wide range of research that has focused on these safety concerns. The two issues addressed have been the ability to penetrate the skin, and the toxicity of these nano particles. 

There have been a number of studies published, and the Federal Government's Therapeutic Goods Administration (TGA) has been consistently reviewing that scientific research. Their first review was published in 2006, and their latest was published in January 2017. The TGA has accepted the overwhelming conclusions in those research papers - that there is no cause for these concerns.

"The majority of in vitro studies (using both animal and human skin) and in vivo studies have shown that both ZnO and TiO2 NPs [nano particles] either do not penetrate or minimally penetrate the stratum corneum and underlying layers of skin. This suggests that systemic absorption, hence toxicity, is highly unlikely," the TGA reported.

"In conclusion, on current evidence, neither TiO2 nor ZnO NPs are likely to cause harm when used as ingredients in sunscreens and when sunscreens are used as directed." (1.)

For a copy of that report, click here.


*Source: http://health.howstuffworks.com/skin-care/beauty/sun-care/spf.htm

*Source: http://www.standards.org.au/OurOrganisation/News/Documents/120615%20Sunscreen%20SPF%2050+.pdf

(1.) Literature review on the safety of titanium dioxide and zinc oxide nanoparticles in sunscreens, Therapeutic Goods Administration (TGA), January 11, 2017. See https://www.tga.gov.au/literature-review-safety-titanium-dioxide-and-zinc-oxide-nanoparticles-sunscreens