Sunscreens: why we need them, how they work, and what to look for.

Sunscreens: Why we need them, How they work, What to look for

Article published in October issue of The Natural Parent Magazine by Katherine Greer

We need sunscreen to help protect us from UV radiation, the main cause of non melanoma skin cancers. 68,000 non melanoma skin cancers are diagnosed in New Zealand yearly representing 80% of all cancers. UV radiation also plays a key role in melanoma, the deadliest form of skin cancer.

We have the highest melanoma rate in the world. In 2010 there were 2341 new cases and 324 died close to the road toll. Melanoma is the most commonly registered cancer in men under 45 and the second most commonly registered cancer in women of the same age group. Melanoma is very uncommon in children but sun burn increases risk of melanoma later in life.

Ultraviolet Radiation UVA UVB

To better understand how sunscreens work to help prevent skin cancers we need to know more about the differences between UVA and UVB radiation.

Ultraviolet (UV) radiation is part of the light spectrum that reaches the earth from the sun. It has wavelengths shorter than visible light, making it invisible to the naked eye. These wavelengths are classified as UVA and UVB.

Ultraviolet B (UVB) is the shorter wave UV ray (wavelength 290 - 320nm) that causes sunburns, skin damage, and can cause skin cancer. Most UVB rays are intercepted by the ozone layer but with its depletion more are reaching the earth's surface. UVB intensity varies by season, location, and time of day with the most significant amount between 10 AM and 4 PM from September to April. However, UVB rays can burn and damage your skin year-round, especially at high altitudes as UV rays increase 4% - 5% with every 300 meters above sea level. Reflective surfaces such as snow or ice, also bounce back up to 80 percent of the rays so that they hit the skin twice. UVB rays do not significantly penetrate glass.

Ultraviolet A (UVA) is the longer wave UV ray (320- 400nm) and penetrate the skin more deeply than UVB rays causing skin damage, premature skin aging, and can cause skin cancer.

UVA rays account for up to 95% of the UV radiation reaching the Earth's surface. Although they are less intense than UVB, UVA rays are 30 to 50 times more prevalent. They are present with relatively equal intensity during all daylight hours throughout the year, and can penetrate clouds and glass.


UVA and Tanning
UVA is the tanning ray, and tanning, whether from the sun or sun beds causes cumulative damage over time. A tan results from injury to the skin's DNA; the skin darkens in an imperfect attempt to prevent further DNA damage. These imperfections, or mutations, can lead to skin cancer. Some people believe that a tan provides UV protection and that tanning is safe. There is no such thing as a safe tan and it will only provide your skin with a SPF 3.

Indoor Tanning
Tanning booths primarily emit doses of UVA as much as 12 times that of the sun. People who use tanning beds are twice as likely to develop non melanoma skin cancers and exposure to tanning beds in youth increases melanoma risk by 75 percent.

Both UVA and UVB cause eye damage, including cataracts and suppress skin immune function.

Sunscreens
Sunscreens are products containing filters that help prevent the sun's ultraviolet (UV) radiation from damaging the skin. There are two broad types: Physical Sunscreens and Chemical Sunscreens, many sunscreens contain a mixture of chemical and physical active ingredients to increase the SPF.

Physical Sunscreen
Physical blockers come in two types: zinc oxide and titanium dioxide, natural minerals micronized to fine powders that sit on the skin and deflect the UV rays. The benefit of physical blockers is that they don’t decompose through sun exposure so theoretically have a longer life on your skin. Zinc Oxide is particularly effective in blocking the full spectrum of UVA rays. The downside is they tend to feel greasy, thick and clog the pores of the skin. One of the issues with the mineral blocks is their opaqueness; they leave a white film on the skin. The processing of the zinc oxide and titanium dioxide into nano particles make products transparent, but there is doubt on the safety of this technology.

Chemical Sunscreens contain carbon compounds made in a laboratory that neutralised the effects of the UV rays.

Sunscreen ratings
Sunscreens contain a sun protection factor (SPF), this is an indication of how long you can stay in the sun without burning if the sunscreen is applied correctly. This time will vary depending on skin type and the strength of the UV rays. The SPF factor measures the UVB rays only, the SPF scale is not linear: SPF 15 blocks 93% of UVB rays, SPF 30 blocks 97%, SPF 50 blocks 98%. If you have fair skin with a burn time of 10 minutes an SPF 30 should give you 30 times more protection (10min x 30 = 300 min or 5 hours}.

Broad-Spectrum
The Australian/New Zealand Sunscreen standards, the United Sates FDA and the European Commission all require a sunscreen to provide UVA protection of at least 1/3 of the labelled SPF, The FDA and the European Commission also require a minimum critical wavelength of 370nm in sunscreen formulations before they can be labelled Broad Spectrum.
The broad spectrum statement and SPF value together provides a measure of both UVB and UVA protection, with increasing SPF values indicating a proportional increase in UVA protection.

Water Resistant
Water Resistant Sunscreen means that the sunscreen retains its stated SPF value after a certain time in water or while sweating. Products manufactured in Australian and New Zealand can claim up to 4 hours water resistant, The FDA only allows the claims Water Resistant 40 min or 80 min to be used on sunscreens made in the USA.

What to look for in a Sun Screen

Buy a SPF 30 or SPF 50 broad Spectrum sunscreen. The new Australian/New Zealand standard limits SPF claims to 50 in line with other international standards. Above SPF 50+ the additional protection is very small. High SPF values are a problem as people use them to stay out longer in the sun during which time they receive large doses of UVA radiation. 

Not all sunscreens with the same SPF's are equal, some will stay on longer than others during exercise and some run off as soon as they come into contact with water including sweat. If you are exercising or swimming select a water resistant sunscreen remembering an extremely highly water resistant product made in European or the USA can only state 80min water resistant even if it provides 4 + hours protection.

Our skin is the largest organ we have so ingredients do matter - look for sunscreens with 3% avobenzone , Mexoryl SX or micronized Zinc Oxide as they safely protect skin from harmful UVA radiation. The Environmental Watch Group has rated Oxybenzone, a commonly used UVA absorber as a moderately high hazard and octinoxate a widely used UVB absorber a moderate hazard.

The EWG also recommends lotions over sprays, to avoid sunscreens with Vitamin A, and sunscreens with insect repellent.
For children and those with sensitive skin select a sunscreen with a natural base.

Check the use by date of the sunscreens you buy and don't use that expired tube left over from last summer!

Sun Safety basics

Cover up, wear a hat and sunglasses, find or make shade, keep babies and toddlers out of the sun as much as possible, keep your teenager away from sun beds, wear sunscreen and lip balms, check your skin regularly and have anything unusual seen to immediately.
 
Author: Katherine Greer, Managing Director of Hydro Surf. When I started surfing 30 years ago, there were no water resistant sunscreens on the NZ market. I sourced Aloe Up, a sports sunscreen made specifically for active people, to protect my and young children's skins while surfing. Hydro Surf now distributes Aloe Up in New Zealand. For more information and retailers go to www.aloeup.co.nz.