How to choose and use a sunscreen

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 is most suitable depends on many factors such as how sensitive the skin is to burning and to cosmetics, how dry or oily the skin is, previous sun and skin cancer history and medical history.

Why use a sunscreen?

Sunscreen is mainly used to protect the skin against ultraviolet radiation, which damages the skin.

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.

For these reasons sun protection is strongly recommended throughout our lifetime.

Sunscreens 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.

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).

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, 2 mg/cm2.This is 6 teaspoons of lotion for the body of one average adult person.

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 50 or more offer a 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?

Selecting a sunscreen depends on 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 general medical history.

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.  

Dry or oily skin

During activity

If you plan to be active outdoors and may get wet or sweaty, choose a sunscreen that is labelled “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, for example, SPF 15 – Water resistant 40 min.

How to use a sunscreen

What about vitamin D?

If you have fair skin you may make enough vitamin D after only 5 minutes of midday summer sun activity when wearing shorts and T shirt.

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