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Get ready for the sun

Nov. 15, 2016


We all know the slip, slop, slap drill when it comes to the sun, but there is much confusion about sunscreens and the level of protection they give. With an increasing array to choose from it is important to understand what the labels actually mean.

Harmful rays

Ultraviolet radiation from the sun is transmitted in three wavelengths; UVA, UVB and UVC. UVC does not penetrate the earth's atmosphere, so we only need to protect against UVA and UVB.

Ultraviolet irradiation in the form of UVA is associated with skin ageing. UVA affects the elastin in the skin and leads to wrinkles and sun-induced skin ageing (for example coarse wrinkles, leathery skin and brown spots), as well as skin cancer. UVA can penetrate window glass and penetrates the skin more deeply than UVB. UVA protection in a sunscreen will help defend the skin against ageing and skin cancer.

UVB is the form of UV irradiation most responsible for reddening the skin, sunburn and causes skin cancers including malignant melanoma and basal cell carcinoma. UVB protection in a sunscreen will protect against sun burn and skin cancers.

What is SPF?

Sun protection factor (SPF) numbers were introduced in 1962 to measure a sunscreen's effect against UVB rays. SPF is a relative measure of how long a sunscreen will protect you from UVB rays. The important thing to note is that it does not give a measure of protection against UVA, so is only part of the information required when choosing a sunscreen. The SPF of a sunscreen is derived by taking the time it takes you to burn with a sunscreen and dividing it by the time taken for you to burn without a sunscreen. For example, if you burn in 300 minutes with a sunscreen and 10 minutes without a sunscreen, this is 300/10 = 30. So, the sunscreen will have an SPF of 30.

Minutes to burn without sunscreen x SPF number = maximum sun exposure time

If you burn after 10 minutes of sun exposure, an SPF of 15 will allow you to be in the sun for up to 150 minutes without burning. But before you grab your calculatorand head for the beach, you should know that this equation is not accurate. Generally, far less sunscreen is applied than should be, lessening the protection. In the real world, the average sun worshipper uses half the amount of sunscreen used in the laboratory, which could result in a sunburn in half the time.

The very confusing issue about SPF numbers are that they are non-linear. Doubling the SPF rating does not give you double the protection. SPF 15 filters about 93% of UVB rays; SPF 30 filters about 97% of UVB rays; and SPF 50 filters about 98% of UVB rays. So swapping from an SPF of 30 to 50 only gives 1% more protection.

No UVA Protection?

The most misunderstood part of sunscreen is whether or not it protects against UVA. UVA is around even on an overcast day and it can penetrate through window glass. Like UVB, it's also related to an increased risk of skin cancer, but unlike UVB, it doesn't cause sunburn, but it leads to darkening and aging.

The one way to tell whether your sunscreen offers UVA coverage are the words broad spectrum on the label. Overseas sunscreen is beginning to be labelled with the amount of UVA protection – you may see this in the UK, EU and Japan.

Always choose a sunscreen which has at least one of its ingredients that protects across the full UVA range. These include titanium dioxide, zinc oxide, avobenzone, ecamsule, bemotrizinol and bisoctrizole.

Do SPF Moisturisers work?

Theoretically SPF rated moisturisers should work just as well as sunscreens in terms of protection against UVB. However, they tend to be applied very thinly, very infrequently and are not rub resistant or water resistant. Most of them do not offer UVA protection. They are probably adequate for very small amounts of UVB exposure, for example popping in and out of the car, or getting the post from your letter box. For any longer exposure a sunscreen is a better option.

What does water-resistant sunscreen do?

The term water resistant means that the SPF is maintained for up to 40 minutes while swimming or sweating. Very water resistant means the SPF is maintained for 80 minutes. The FDA recently stopped sunscreens being labelled as "waterproof" because it was misleading.

Sensitive Skin

Active ingredients in sunscreens come in two forms, mineral and chemical filters. Each uses a different mechanism for protecting skin and maintaining stability in sunlight. The most common sunscreens on the market contain chemical filters. These products typically include a combination of two to six of these active ingredients: oxybenzone, avobenzone, octisalate, octocrylene, homosalate and octinoxate. Mineral sunscreens use zinc oxide andor titanium dioxide, and typically are harder to rub in and can leave the skin looking white. A handful of products combine zinc oxide with chemical filters. It is the chemical filters that most often cause skin irritation and should be avoided if you are sensitive to sunscreen or even allergic to it.

The Bottom Line

A sunscreen with a higher SPF does offer higher protection against UVB rays, but once you get past SPF 30, protection doesn't increase much. The higher number may give you a false sense of protection. SPF does not apply to UVA rays so look for a Broad-Spectrum product.

Apply sunscreen 15 to 30 minutes before you go outside.

For lotions, a good rule of thumb is a teaspoon per body part or area: 1 teaspoon for your face, head, and neck; 1 for each arm; 1 for each leg; 1 for your chest and abdomen; and 1 for your back and the back of your neck. Use far more than you think is necessary.

For sprays, apply as much as can be rubbed in, then repeat.

Reapply every 2 hours and after swimming or sweating.

Use spray sunscreens carefully. The FDA has said it is exploring the risks of inhaling spray sunscreens. Until we know more, our experts say to avoid using sprays on children, and do not spray them directly on your face. Instead, spray sunscreen onto your hands then apply it to your face. If you do use a spray on a child, follow that advice as well. Sprays are flammable, so let them dry before going near an open flame.

Cover up as much skin as possible with clothing.

Always wear a hat – preferably one that covers your hands.

Find the shade!

For more advice go to

https://www.consumer.org.nz/articles/sunscreens

http://www.skincancer.org/prevention/sun-protection/sunscreen/the-skin-cancer-foundations-guide-to-sunscreens

http://www.dermnetnz.org/topics/topical-sunscreen-agents