What are Sunscreens?

Sunscreens are products containing filters  that help prevent the sun's ultraviolet (UV) radiation from damaging  the skin. Two types of ultraviolet radiation,  UVA and UVB damage the skin and increase your risk of skin cancer.  Sunscreens vary in their ability to protect against UVA and UVB, and it is important when choosing a sunscreen to consider the demands you are putting on the product.

There are two broad categories  of UV Filters: chemical[1] and physical.  Sunscreens containing the minerals  Zinc and Titanium Dioxide  are  physical blocks that sit on the surface of the skin to prevent the UVA and UVB rays from penetrating the skin.   Most UV Filters are chemical, they absorb and neutralise the effects of the UV rays.   One of the issues with the mineral blocks is their opaqueness – they leave an unattractive white coloured film on the skin. The processing of the zinc oxide and titanium dioxide into nanoparticles allows formulation of a product  that is transparent, yet reflects all components of UV Radiation but there is doubt on the safety of this technology.

Many sunscreens  contain  a mixture of chemical and physical active ingredients to increase the spf protection.  These sunscreen are thicker, often leave a white film and are more difficult to rub in.

[1] the words chemical and organic are confusing.  Technically chemical sunscreens are considered organic as they are naturally occurring organic compounds.  Inorganic Ingredients Zinc Oxide and Titanium dioxide reflect radiation which is often marketed as “natural, organic or chemical freee” use a chemical process to make the minerals small enough.

What is Ultraviolet Radiation UVA UVB UVC ?

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, UVB, or  UVC.  

Ultraviolet A (UVA) is the longer wave UV ray that causes lasting skin damage, skin aging, and can cause skin cancer. Ultraviolet B (UVB) is the shorter wave UV ray that causes sunburns, skin damage, and can cause skin cancer.  Most UVC is absorbed by the ozone layer and does not reach the earth.

Both UVA and UVB, however, penetrate the atmosphere and play an important role in conditions such as premature skin aging, eye damage  (including cataracts ) and skin cancers. They also suppress the immune system, reducing your ability to fight off these and other maladies.

UV Radiation and Skin Cancer

In New Zealand our skies are relatively clear and unpolluted so we have a high level of  ultraviolet radiation.

By damaging the skin's cellular DNA, excessive UV radiation produces genetic mutations that can lead to skin cancer. Both the U.S. Department of Health and Human Services and the World Health Organization have identified UV as a proven human carcinogen.

UV radiation is considered the main cause of nonmelanoma skin cancers (NMSC), including basal cell carcinoma (BCC) and squamous cell carcinoma (SCC )

UV radiation also plays a key role in melanoma, the deadliest form of skin cancer.  New Zealand has the highest melanoma rate in the World. In 2009 (the latest published data) 213 men and 113 women died from this preventable cancer.  In New Zealand  Melanoma is the most common cancer in men and the second highest for women in the 25 -44 year old age group.    Fair skinned people are at higher risk but in 2009 there were 7 Maori and  Pacifica melanoma deaths.


Most of us are exposed to large amounts of UVA throughout our lifetime.  UVA rays account for up to 95 percent 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, which penetrates the skin more deeply than UVB, has long been known to play a major part in skin aging and wrinkling  but until recently scientists believed it did not cause significant damage in areas of the epidermis (outermost skin layer) where most skin cancers occur. Studies over the past two decades, however, show that UVA damages skin cells called keratinocytes in the basal layer of the epidermis, where most skin cancers occur. (Basal and squamous cells are types of keratinocytes.) UVA contributes to and may even initiate the development of skin cancers.

UVA and Tanning

UVA is the dominant tanning ray, and we now know that tanning, whether outdoors or in a salon, 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.  A tan will only provide your skin with an spf 3 protection

Indoor Tanning

Tanning booths primarily emit UVA. The high-pressure sunlamps used in tanning salons emit doses of UVA as much as 12 times that of the sun. Not surprisingly, people who use tanning salons are 2.5 times more likely to develop squamous cell carcinoma, and 1.5 times more likely to develop basal cell carcinoma. According to recent research, first exposure to tanning beds in youth increases melanoma risk by 75 percent.


UVB, the chief cause of skin reddening and sunburn, tends to damage the skin's more superficial epidermal layers. It plays a key role in the development of skin cancer and a contributory role in tanning and photoaging. Its intensity varies by season, location, and time of day. The most significant amount of UVB hits   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 and on reflective surfaces such as snow or ice, which bounce back up to 80 percent of the rays so that they hit the skin twice. UVB rays do not significantly penetrate glass.

What Does Broad-Spectrum Mean?

Broad-spectrum sunscreens protect the skin from both UVA  (long rays ) and UVB rays. It was once Sthought that only the UVB rays were off concern but it is now known that UVA rays are responsible for aging the skin and can also cause skin cancers.

What Is SPF?

Sunscreens contain an 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  to date there are no measuring system for UVA rays.

The SPF scale is not linear:  SPF 15 blocks 93% of UVB rays, SPF 30 blocks 97% and SPF 50 98%. 

Above SPF 50+ the additional protection is very small. In fact, high SPF values are a problem. Studies have shown that people use them to stay out longer in the sun, using sunburn as a warning to take cover. During this time you can receive large doses of UVA radiation.

The new Australian/New Zealand standard limits SPF claims to 50 in line with other international standards.

 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 however most sunscreens will clearly state to reapply after exercise or swimming or every 2 hours. 

You also need to take into account that Ultraviolet  rays increase 4% - 5% with every 300 meters above sea level.  

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. 

Sweating  while outside is linked to skin cancer, a wet skin absorbs more UV rays which means exercising in the sun can be more dangerous than relaxing in the sun. 

It is important when selecting a sunscreen that you consider the demands you are placing on product and to purchase a sunscreen that will give you the appropriate protection.

How to apply Sunscreen correctly

To receive the full SPF protection sunscreen must be applied correctly so follow the application recommendations.

Apply sunscreen liberally and frequently every two hours - at least a teaspoon for each limb, front and back of the body and half a teaspoon for the face, neck and ears. You should apply one cupped adult hand (30 to 40 ml) of sunscreen for an adult body.

 If you are exercising purchase a sports specific sunscreen and give you body a generous and even coating preferably naked As an guideline use at less a shot glass full to cover your body and reapply as directed.


Choosing a Sunscreen that is right for you

When choosing a sunscreen consider the demands you are putting on the product.  Sweating  while outside is linked to skin cancer, a wet skin absorbs more UV rays which means exercising in the sun can be more dangerous than relaxing in the sun.  If you are exercising outdoors choice a sports specific sunscreen that clearly states it is highly water and sweat resistant.  If you spend hours in the sun exercising you need a highly technical product designed specifically for athletes.

What Chemicals to avoid in Sunscreen?

The EWG (Environmental Working Group) recommend avoiding sunscreen containing oxybenzone and Vitamin A

Commonly used in sunscreens, the chemical oxybenzone penetrates the skin, gets into the bloodstream and acts like estrogen in the body. It can trigger allergic reactions. Data are preliminary, but studies have found a link between higher concentrations of oxybenzone and health harms. One study has linked oxybenzone to endometriosis in older women; another found that women with higher levels of oxybenzone during pregnancy had lower birth weight daughters.


A study by U.S. government scientists suggests that retinyl palmitate, a form of vitamin A, may speed the development of skin tumors and lesions when applied to the skin in the presence of sunlight (NTP 2012).

The evidence, while not definitive, is troubling.

Vitamin A is an antioxidant added to skin products because manufacturers believe it slows skin aging. They may be right in the case of lotions and night creams used indoors, but the federal study raised the possibility that it may speed the growth of cancerous tumors when used on skin exposed to sunlight.

Scientists have found that vitamin A can spur excess skin growth, known as hyperplasia and that in sunlight retinyl palmitate can form free radicals that damage DNA (NTP 2000).


Does having a tan mean you don't need as much sunscreen?

NO. A tan is a sign that skin damage has already started. Any further UV radiation will only add to the damage, resulting in wrinkled leathery skin and possibly skin cancer later in life. A tan only provides the skin with an spf3 protection.

Do I need a special sunscreen for my child?

Proper protection from the sun is more important during childhood than at any other time in life. 

We receive 80% of our  life time UV radiation by the time we reach 18 and childhood and teenage sunburns increase the risk of skin cancer in adulthood .

Sunscreens that are specially formulated for children have a mild base designed especially for their sensitive skin. But there's no reason why children shouldn't use the family sunscreen, provided it doesn't irritate their skin. Test a small amount on the inside of their forearm first.

Keep babies and toddlers out of the sun as much as possible. The best protection for them is staying in the shade and using cover-up clothing - as it is for everybody.

Why use Sunscreen Summary

Skin cancers – melanoma and non melanoma are primarily caused by too much UVA & UVB ultraviolet radiation from the sun or sun beds. 

In New Zealand our skies are relatively clear and unpolluted so we have a high level of  ultraviolet radiation.

You can burn on an overcast day especially during 11am – 4pm

A tan will only provide your skin with an SPF 3 protection.

Protective Measures

Protect yourself from UV radiation, both indoors and out. Always seek the shade outdoors, especially between 10 AM and 4 PM. And since UVA penetrates glass, consider adding flat, tinted UV-protective film to your car's side and rear windows as well as to house and business windows. This film blocks up to 99.9 percent of UV radiation and lets in up to 80 percent of visible light.

Outdoors, dress to limit UV exposure: Special sun-protective clothes with UPF (ultraviolet protection factor) indicate how much UV radiation can penetrate the fabric; the higher the UPF, the better. A shirt with an UPF of 30, for example, means that just 1/30th of the sun's UV radiation can reach the skin.  

Bright- or dark-colored clothing reflect more UV radiation than do pastels and bleached cottons; and tightly woven, loose-fitting clothes provide more of a barrier between your skin and the sun.

Consider the demands you will placing on your sunscreen and purchase an appropriate product that will meet your needs then apply it correctly.

Broad-brimmed hats and UV-blocking sunglasses help shield the sensitive skin on your head, neck, and around the eyes - areas that usually sustain a lot of sun damage.