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How to choose and use sunscreens

Author: Dr Louise Reiche, Dermatologist, 2007. Updated by Vanessa Ngan, Staff Writer, August 2012.

Introduction

Improved knowledge related to the sun and technology advances have made sunscreen issues more complex. Which sunscreen product 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.

Why use sunscreens?

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 sunburn and contribute to skin cancers. UVA penetrates deeper and large or prolonged exposure may also cause burning, premature skin ageing and skin cancers. Both UVA and UVB suppress skin immune function. For these reasons it is strongly recommended that sun protection plays an important role throughout our lifetime.

Using sunscreen products is just one of the many approaches we can take to protect ourselves from the dangers of sunlight. However, they do not provide total protection and should be used in conjunction with other sun protective measures such as wearing sun protective clothing and staying indoors or out of the sun during peak sunshine hours in the day.

What sunscreen should I choose?

Sunscreen products protect the skin by absorbing and/or blocking harmful UVL. See topical sunscreen agents for a list of the active ingredients that make up the many sunscreen preparations available. All sunscreen products must be tested, classified and labeled according to their sun protective capabilities (see sunscreen testing and classification).

SPF for UVB protection

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. For example, if it takes 10 minutes to burn without a sunscreen and 150 minutes to burn with a sunscreen, then the SPF of that sunscreen is 15 (150/10). The higher the SPF number, the better is the expected protection. A sunscreen with a SPF 15 provides about 94% protection against UVB. Protection against UVB is increased to 97% with SPF 30 and increased to 98% with SPF 50+. As you can see the difference in protection when going from a sunscreen with SPF 15 to one with SPF 30 or even 50+ differs only by 3-4%. In addition, this protection is only provided if sunscreens are applied in quantities similar to the ones used for testing, i.e. 2 mg/cm2 (or 6 teaspoons of lotion for the body of one average adult person). In reality, 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 or after heavy sweating or swimming. Therefore, the actual protection may be a lot less than the tests indicate. A sunscreen with SPF 15+ should provide adequate protection as long as it is being used correctly. Sunscreens with SPF 30 or more may offer some safety margin, since most people don’t apply sunscreens as heavily or as often as they should.

Broad Spectrum for UVA protection

With increasing awareness about UVA-induced skin damage, it is important to choose a sunscreen that also protects against UVA radiation. These products are labeled with the statement “Broad Spectrum”. Always choose a sunscreen which has at least one of its ingredients that protects across the full UVA range. These include the metal oxides, titanium dioxide and zinc oxide, and the chemical absorbers, avobenzone, ecamsule, bemotrizinol and bisoctrizole.

The UVA protection factor (UVA-PF) must be at least 1/3 of the labeled SPF, so choosing a sunscreen with a higher SPF will also mean higher UVA protection.

Photostability

Choose a sunscreen that is photostable to ensure that it will not breakdown and become ineffective on exposure to sunlight. Octocrylene, bemotrizinol and bisoctrizole are photostable agents and when combined with other chemical absorbing agents improve the overall photostability of the sunscreen product.

What sunscreen can I use?

When selecting a sunscreen what is 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.

If you have fair skin that burns easily you should choose a broad spectrum sunscreen with a high SPF e.g. 50+ 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.

Sensitive skin

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 have a sunscreen allergy and 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. alcohol-based lotion, sprays or gels. Lighter sunscreens are also better in hairy skin areas. Special sunscreen sticks are suitable for noses, lips and around the eyes.

Activity

If you plan to be active outdoors and may get wet or sweaty, choose a sunscreen that is labeled “water resistant”. These products should also show the amount of time you can expect to get the declared SPF level of protection while swimming or sweating, e.g. SPF 15 – Water resistant 40 min.

How to use sunscreens

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.

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