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SPF stands for Sun Protection Factor and is the system used worldwide to determine how much protection a sunscreen provides, applied to the skin at a thickness of 2 mg/cm2. The test works out how much UV radiation (mostly UVB) it takes to cause a barely detectable sunburn on a given person with and without sunscreen applied. For example, if it takes 10 minutes to burn without a sunscreen and 100 minutes to burn with a sunscreen, then the SPF of that sunscreen is 10 (100/10).
A sunscreen with a SPF of 15 provides >93% protection against UVB. Protection against UVB is increased to 97% with SPF of 30+. The difference between a SPF 15 and a SPF 30 sunscreen may not have a noticeable difference in actual use as the effectiveness of a sunscreen has more to do with how much of it is applied, how often it is applied, whether the person is sweating heavily or being exposed to water. Hence a sunscreen with SPF 15+ should provide adequate protection as long as it is being used correctly. However, most people apply their sunscreen at about one third the thickness used for testing; they fail to apply it to all exposed areas of skin; and they forget to reapply it every couple of hours. Therefore, the actual protection may be a lot less than the tests indicate.
Currently there is no internationally agreed test for measuring UVA protection in human skin. An estimate is made by a laboratory test in which the proportion of radiation passing through a measured amount of sunscreen is determined. To ensure some protection against UVA, products with physical blocking agents making up some of the active ingredients are recommended.
* Use a good broad-spectrum sunscreen of at least SPF 15 and made up of a benzophenone chemical absorber plus a physical blocker (titanium dioxide or zinc oxide).
* Choose a product that complies with the current Australian and New Zealand Standard for Sunscreens (AS/NZS2604:1998), or equivalent in other countries.
* Apply sunscreen liberally to all sun-exposed areas so that it forms a film when initially applied. Most people use sunscreens improperly by not applying enough.
* It takes 20-30 minutes for sunscreen to be absorbed by the skin and it can be rubbed off very easily, so apply it at least half an hour before going out in the sun. Reapply after half an hour so that the ‘mountains’ as well as the ‘valleys’ are protected (imagine you are painting a wall – two coats of paint provide a more even cover than one).
* Re-apply sunscreen every 2 hours if staying out in the sun for more than an hour during the day.
* Re-apply immediately after swimming, excessive sweating, or if rubbed off by clothing or toweling. This should be the case even if the product claims to be “water resistant”.
* Insect repellents reduce the sunscreen’s SPF so when using together, use a sunscreen with a higher SPF and re-apply more often.
Alcohol-based lotions, sprays or gels are better for oily or hairy skin. Creams are suitable for dry skin, and milky lotions are the easiest to apply. Special sticks are suitable for noses, lips and around the eyes.
Type of SunBlock
Which sunscreen, if any, should I use?
Improved knowledge related to the sun and technology advances have made sunscreen issues more complex. Which sunscreen would be best for you, depends on many factors such as how sensitive your skin is to burning and to cosmetics, how dry or oily your skin is, previous sun and skin cancer history and your medical history
Sunlight generates warmth (infra-red) that we can feel, visible light (that our eyes can see in daylight) and ultraviolet light (UVL) which we cannot see or feel but which can penetrate our skin. The UVL that reaches the earth is grouped into shorter UVB and longer UVA wavelengths. Our skin makes Vitamin D from small amounts of UVB but larger amounts may cause burning and contribute to skin cancers. UVA penetrates deeper. Large or prolonged exposure may also cause burning, premature skin ageing and skin cancers. Both UVA and UVB suppress skin immune function. Heat and wind can exaggerate the damaging effects of ultraviolet light. New Zealand’s UVL is stronger from September to April so the daylight saving months are a good guide to when sunscreens may be needed regularly.
SPF stands for sun protection factor. This tells us how much longer we could expect to be exposed to UVB before burning compared to no sunscreen. The higher the number, the better is the expected protection. It is still being resolved internationally how to best rate UVA protection. Meanwhile choose a sunscreen that offers broad spectrum cover. In the future sunscreens may also include immune protection factors.
Sensitive skin
If you have fair skin that burns easily you should choose a broad spectrum sunscreen with a high SPF e.g. 30+ If you have skin that tans readily you could choose a broad spectrum sunscreen with intermediate SPF e.g. 8-15+ If you have darkly pigmented skin and do not suffer from a sun / photosensitivity problem, you do not need sunscreen.
If you have sensitive skin that has trouble tolerating sunscreens or cosmetics, look for hypoallergenic / low irritant sunscreens. You may like to try a variety of sunscreen samples before deciding what you will use regularly. If you are still having rashes you might need to undergo allergy patch testing to identify a particular ingredient in sunscreens that is causing the problem. Talk with your dermatologist about this if necessary.
Dry / Oily skin
If your skin is dry you would benefit from a sunscreen with a moisturising base e.g. sunscreen creams or ointments. If you have oily skin or readily develop acne, choose a sunscreen in a lighter base, e.g. lotion or gel. Lighter sunscreens are also better in hairy skin areas.
Activity
If you plan to be active outdoors and may get wet or sweaty, choose a sunscreen that is water resistant and likely to be longer lasting or rub resistant.
What about Vitamin D?
If you have fair skin you may need only 5 minutes of midday summer sun activity in shorts and t-shirt without sunscreen to make enough. You will need longer or greater skin exposure if your skin is darker. Being physically active outdoors helps you make more Vitamin D than resting in the sun. If you are over 50 years old (ageing skin is not as good at making Vitamin D), immunosuppressed or have had previous skin cancers, you are better to apply sunscreen and talk to your doctor about Vitamin D supplements.
Skin phototype
The classification of skin type known as the Fitzpatrick skin type (or phototype) depends on the amount of melanin pigment in the skin. This is determined by constitutional colour (white, brown or black skin) and the result of exposure to ultraviolet radiation (tanning). Pale or white skin burns easily and tans slowly and poorly: it needs more protection against sun exposure. Darker skin burns less and tans more easily. It is also more prone to develop postinflammatory pigmentation after injury (brown marks).| Skin type | Typical Features | Tanning ability |
|---|---|---|
| I | Pale white skin, blue/hazel eyes, blond/red hair | Always burns, does not tan |
| II | Fair skin, blue eyes | Burns easily, tans poorly |
| III | Darker white skin | Tans after initial burn |
| IV | Light brown skin | Burns minimally, tans easily |
| V | Brown skin | Rarely burns, tans darkly easily |
| VI | Dark brown or black skin | Never burns, always tans darkly |
