Using sunscreen to help protect skin

Sunscreen is a useful tool in helping to protect your exposed skin from ultraviolet (UV) radiation from the sun, particularly in the summer months when the UV levels are high. However, choosing the right sunscreen is important, as is applying it correctly. You should not rely on sunscreen as your only form of sun protection. Over exposure to UV radiation from the sun is the main cause of skin cancer, including melanoma.

Tips for suncreen use

• No sunscreen will completely shield you from the effects of ultraviolet radiation.
• Also use other forms of sun protection: minimise time spent in the sun from 11am to 4pm during the daylight saving months; wear a hat and protective clothing; wear sunscreen on uncovered skin; wear sunglasses and stay in the shade if you can.
• Sunscreen should be used to decrease exposure to UV radiation, not to increase the amount of time you spend in the sun.
• The Cancer Society recommends the use of broad spectrum, SPF30+ sunscreen. Use water-resistant sunscreen if in the water. 
• Apply adequate amounts of sunscreen 15 minutes before going outside, and re-apply every two hours, especially if swimming or perspiring (sweating).

How much protection does sunscreen give?

The protection a sunscreen offers is affected by its sun protection factor (SPF) rating, whether it is broad spectrum, how evenly and how thickly you apply it, and how long you spend in the sun. The longer the time spent in the sun, the more UV radiation accumulates and the greater the potential for burning.

Even if you are not very active, sunscreen tends to rub off gradually and therefore needs to be reapplied regularly. This applies particularly to children because they are active.

What is SPF?

The sun protection factor (SPF) number is a ranking system that shows how much protection is being offered against UV radiation. The higher the SPF number, the more UV radiation is filtered out and the greater the protection. SPF gives a general guide to sun protection but does not determine how long it will take for a person to be sunburnt. The amount of time it takes to be sunburnt depends on the level of UV radiation, and varies according to the time of day, the time of year, the weather, and the person’s skin colour.

No matter how high the SPF rating, no sunscreen can screen out all UV radiation. All sunscreens are filters allowing some UV radiation to pass through to the skin. The Cancer Society advises that SPF30+ sunscreen is sufficient for sun protection if applied correctly. A higher SPF+ sunscreen may give a sense of false assurance regarding the length of time one can spend safely in the sun.

How does sunscreen work?

Sunscreens contain either chemical blockers that absorb UV radiation, dispersing it as heat before it can damage the cells; or physical blockers that reflect UV radiation away from the skin. Some sunscreens contain both.

Broad spectrum sunscreen

A broad spectrum sunscreen gives extra protection because it screens out most of the UVA (shorter wave length) radiation as well as UVB.

UVA penetrates deep into the skin, affecting the cells that lie deep under the skin’s surface. It causes aging of the skin, and long-term damage.

UVB radiation penetrates the skin’s top layer, causing sunburn, and long-term damage. It is now known that both UVA and UVB contribute to the development of skin cancer.

Water resistance

A water resistance claim of two hours means the sunscreen should retain its full SPF protection even after two hours in the water. However, it is wise to reapply sunscreen after any water sports, sweating or towel drying.

Is sunscreen safe?

To date, there is no scientific evidence showing long-term side effects following regular use of sunscreen.

Short-term side effects may include reactions, such as skin irritation, stinging or a rash. If these side effects occur, try another brand and look for products that are fragrance-free, or labelled as suitable for sensitive skin. Products containing titanium dioxide and zinc oxide may be the most suitable.

What are nanoparticles?

Some sunscreens contain nanoparticles, which are very small particles invisible to the human eye. Recently, there have been questions raised about the safety of sunscreens that contain nanoparticles. To date, the best available evidence suggests that nanoparticles used in sunscreens are not a health risk, because they remain on the surface of the skin and do not pass through to living skin cells.

New research that considers the safety of nanoparticles will be examined as it becomes available.

How to apply sunscreen

Apply sunscreen 15 minutes before sun exposure to allow it time to dry and be absorbed into the skin.

Use a generous amount of sunscreen. The average-sized adult should apply at least half a teaspoon of sunscreen to each arm, and to the face (including the ears and neck), and at least a teaspoon to each leg, the front of body and the back of body. That is, 35ml of sunscreen for one full body application.

The protective effect of sunscreen depends on correct application. People frequently only receive about 30% of the SPF protection level because they do not apply enough sunscreen. No matter what the sunscreen directions say, always reapply sunscreen every two hours when you are outdoors. Sunscreen can be easily wiped or perspired off, and you need to keep applying sunscreen to get the best protection.

How long can you keep sunscreen?

Most sunscreens last about two or three years and should be stored below 30ºC. Check the expiry date, and storage conditions on the label. If sunscreen is left in excessive heat (eg. in the sun, or glovebox of a hot car), over time the sunscreen may deteriorate faster and may not give as much protection.

Choosing a sunscreen

• Choose a broad spectrum SPF30+ water-resistant sunscreen.
• Sunscreen can be bought as a cream, lotion, milk or gel. Choose the one that best suits your skin type and activity.
• If you do not want sunscreen residue left on your hands, a gel may work best for you. Price is not always an indication of quality.
• If using sunscreen on a baby or toddler’s skin, test it on a small area of their skin first and leave for 24 hours to check for a reaction. Stop use immediately if there is a reaction.

The Ultraviolet Index (UVI)

The Ultraviolet Index (UVI) is an international, scientific measure of the level of ultraviolet radiation in the environment. The higher the number, the greater the risk of skin damage. The Cancer Society advises sun protection in New Zealand between September and April (especially between 11am and 4pm), or when the UVI is 3 or higher.

Related topics

Also see Melanoma and Sunburn and Sun - clothing and hats

Original material provided by the Cancer Society of New Zealand, December 2010. Edited by everybody, December 2010.