Sunscreen: How it Works, How to Choose

The Benefits of Sunscreen

Sunscreen is one of the most effective ways of reducing exposure to ultraviolet (UV) radiation, the main cause of skin cancer. It has been proven to reduce the risks of melanoma1, squamous cell carcinoma2, and solar keratoses3. It has also been shown to reduce visible signs of skin ageing4.

How Does Sunscreen Work?

Sun damage and skin cancer are caused by ultraviolet radiation in sunlight damaging DNA in the genes of skin cells. Sunscreens help prevent UV from reaching the genes, either by absorbing or reflecting UV radiation.

Physical / Mineral Sunscreens

Physical sunscreens create a barrier on top of the skin which UV radiation cannot easily penetrate — it reflects off the skin. The active ingredients are usually zinc or titanium.5

Chemical Sunscreens

Chemical sunscreens absorb UV radiation, converting it into heat which is released from the skin. There are many different formulations, often used in combination because each chemical protects against a narrow range of wavelengths.

Liposomal Sunscreens

Liposomal sunscreens are a relatively new formulation. Small particles contain the UV-blocking component of sunscreen. They absorb into the uppermost layer of the skin, rather than sitting on top of it (but they do not penetrate the skin or enter the bloodstream).

Advantages and disadvantages of different sunscren types
  Advantages Disadvantages
Physical / Mineral

Physical sunscreens protect from the time they are applied, and usually cause minimal irritation to sensitive skin.

Some physical sunscreens create a visible white film when applied, particularly on dark skin. Some can be thick, greasy and hard to apply. Physical sunscreens are more likely to rub or sweat off.6 Modern physical sunscreens contain very small nanoparticles of active ingredients which are less likely to create a visible film on the skin surface.

Chemical

Chemical sunscreens are usually easier to apply and less visible than physical sunscreens. They are less likely to wash or sweat off.

They need to be applied about 20 minutes prior to sun exposure, to give sufficient time to work effectively. Chemical sunscreens are more likely to cause irritation to sensitive skin.6

Liposomal

Liposomal sunscreens might last longer, theoretically a whole day. Clinical studies have not yet proven this. You should reapply liposomal sunscreens just as you would any other sunscreen.7

Some liposomal sunscreens are expensive.

How to Choose a Sunscreen

Any sunscreen you use should have a sun protection factor (SPF) of at least 30, and provide broad spectrum protection.

Sun Protection Factor

Sun protection factor (SPF) is a measure of how much longer it takes skin to burn with sunscreen than without. A higher SPF number means stronger protection.

Properly applied, SPF 30 filters 96.7% of UV-B radiation, and SPF 50 filters 98%. The difference is relatively small and need not influence your sunscreen choice if there are other factors which are more important to you.

Broad Spectrum Sunscreens

UV radiation occurs in different wavelengths – UV-A and UV-B. A good sunscreen blocks a high proportion of both types. SPF only measures protection against UV-B which causes burning. UV-A causes longer-term changes such as wrinkling, drying and ageing of the skin. Both types of radiation contribute to skin cancer development.

Broad spectrum sunscreens protect against both wavelengths of UV radiation. In Australia, most commercially sunscreens with SPF30 or more provide broad spectrum protection, but you should always check that the label specifies “broad spectrum”.

Other Factors

If your sunscreen is broad spectrum and SPF 30 or more, other factors are a matter of personal preference. You should choose the sunscreen that you are most likely to use.

Things that might influence your choice:

Skin Type

If your skin is very sensitive, choose a sunscreen that is less likely to cause irritation. In general, physical sunscreens, “low irritation” sunscreens and sunscreens marketed for children or babies are less irritant

 If your skin is dry, you may prefer a cream which combines sunscreen with moisturiser. Alternatively, you can use a very light or “sheer” sunscreen and then cover it with make-up or moisturiser.

Swimming and Sweating

If you are swimming or sweating while outside, a chemical sunscreen will usually last better. Some brands specifically formulate sunscreens for “wet skin” or “water sports”.

Longer Duration

If you spend a long time in the sun, particularly if you sometimes forget to reapply, a longer-lasting formulation may be suitable. These include liposomal products, and others containing proprietary combinations of chemical sunscreen components formulated to break down more slowly, e.g. Helioplex in Neutrogena sunscreens.

Easy Application

Aerosol sprays are easy to apply and can be useful for hairy skin or children who might not tolerate having cream or lotion rubbed in to their skin.

These sprays should be applied outdoors where there is less chance of inhalation.8

Price

Many affordable sunscreens are available in supermarkets and discount pharmacies. Some come in large containers suitable for family or workplace use.

If a sunscreen is labelled as SPF 30 or more, and broad spectrum, it should provide good protection providing it is properly applied.

Sunscreen Failure

Some people apply sunscreen and still get sunburnt. Sunscreens on the Australian market are tested to ensure they work as advertised. The most common cause of sunscreen “failure” is not applying it properly.8

Applying and Reapplying

Most people don’t use enough sunscreen9, and they don't cover enough of their body10 For adequate protection, the average adult should use about 45ml or 9 teaspoons of sunscreen:

How much sunscreen to use (in teaspoons) on each body region
How much sunscreen to use (in teaspoons) on each body region
  • one teaspoon of sunscreen applied to the face/head/neck
  • two teaspoons for the torso
  • one teaspoon to each arm/forearm
  • two teaspoons to each leg

 

Sunscreen should be applied 20 minutes before going outside and reapplied every two hours.11

Pump packs are a good way of ensuring adequate sunscreen is applied. Children using pump packs tend to apply more sunscreen than those using sprays or squeeze bottles.12

On a cloudy or cool day, it can be easy to forget to apply and reapply sunscreen. We recommend the SunSmart app for smartphones. It can notify the user when the UV index reaches a level which can damage skin, and remind when to reapply sunscreen.13

Spray-On Sunscreens

It’s common for people not to use enough sunscreen when using a spray-on formulation. Different brands deliver a different amount of sunscreen per second.11 To get adequate protection, ensure that you spray enough to feel wet, and then smear it in with your hand.8

Storage

Sunscreens should be stored below 30° and not used past their expiry date. Do not keep sunscreens in your car.

Sunscreen and Vitamin D Deficiency

Vitamin D deficiency is common in Australia. Since sun exposure is necessary to produce vitamin D, some people are concerned that using sunscreen may lead to low vitamin D levels. Studies have shown that this is not the case. There is no confirmed link between low vitamin D levels and sunscreen use.5

Safety

Potentially any sunscreen could cause problems; it’s not possible to conclusively prove that any product is 100 per cent safe. However, there is strong evidence that the health benefits of sunscreens far outweigh any health risks.

Skin Irritation

Some ingredients in sunscreens irritate sensitive skin. It can be a process of trial and error to find a sunscreen that causes the least irritation.

General principles:

  • Fragrances can cause irritation. Use unscented sunscreens where possible.
  • Physical sunscreens are less likely to irritate the skin than chemical sunscreens.

Nanoparticles

Nanoparticles are very tiny (less than 100nm) particles of zinc or titanium used in some physical sunscreens. They reduce the white greasy appearance common with physical sunscreens and can be easier to apply. Nanoparticles have not been shown to penetrate the skin. There is no current evidence that they are absorbed into the bloodstream or cause any health problems.5, 14

Hormone Disruption and Cancer

Some people have raised concerns that the organic compounds (e.g. oxybenzone) used in chemical sunscreens could cause cancer or disrupt the action of hormones. To date, these effects have been seen only in animals during testing at extremely high doses. It would probably be impossible to replicate these doses in humans using sunscreen, even over many years.8

Recommended Sunscreen

Cetaphil Sun Kids
Cetaphil Sun Kids lotion

There’s no single “best” sunscreen for everyone in all situations. Use a broad spectrum product with SPF 30 or more, and apply it properly and regularly, and you should be well protected, and reduce your skin cancer risk. The “best” sunscreen for you, is the one you are most likely to use.

Sunscreen formulations change frequently. At the time of writing, our favourite is Cetaphil Sun SPF50+ Kids Liposomal Lotion, (even for adults) because of the following benefits:15

  • Suitable for sensitive skin
  • Highest level of protection
  • Reasonable price (significantly cheaper than the “adult” liposomal formulation currently available in Australia)
  • Excellent packaging: The pump pack provides measured quantities of sunscreen and there are clear instructions on how many pumps to use for each body part.
  • Liposomal formulation may last longer between applications.

Disclaimer: This is general information only. Spot Check Clinic gives no guarantee that this product is superior in terms of protection, side effects, or in any other way, to other sunscreens. Notwithstanding our recommendation, Spot Check Clinic takes no responsibility for any adverse events that occur when using this product.

Further Information

For more detailed information about sunscreens, see: