Sunscreen is one of the important ways we can help protect our skin from the damaging ultraviolet (UV) light when outside. It is important to choose the right sunscreen and know how to apply it correctly.
Tips for sunscreen use
- No sunscreen will completely shield you from the effects of ultraviolet radiation – you should also use other forms of sun protection.
- Minimise time spent in the sun from 10am 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 whenever possible.
- 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 of NZ 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 (see below), 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 tend to be 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.
Sunscreen doesn't block all UV radiation
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. Higher SPF+ sunscreens are available; however, they still need to be correctly applied and reapplied regularly.
Does sunscreen prevent skin cancer?
There are three main types of skin cancer: melanoma (the potentially most dangerous form); squamous cell carcinoma (SCC), which often grows slowly, but if not treated can spread; and basal cell carcinoma (BCC), which is usually curable. Solar keratoses are rough, scaly spots that develop on skin that has had a lot of sun exposure. People with solar keratoses have an increased risk of skin cancer.
When used correctly, sunscreen can protect against sunburn and DNA damage to skin from UV radiation exposure. Sunburn, especially in childhood, is a risk factor for melanoma. Preventing sunburn may help reduce melanoma risk and skin damage.
There is evidence that regular sunscreen use may protect against squamous cell carcinoma (SCC). The information is less clear about the extent to which sunscreen prevents melanoma and basal cell carcinoma (BCC). Regular sunscreen users have shown a reduction in development of solar keratoses. Naevi (a type of mole), which frequently develop during childhood, increase the risk of melanoma. It has been shown that regular use of sunscreen in childhood can reduce the development of naevi.
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.
UV radiation consists of UVA, UVB and UVC radiation. UVA penetrates deep into the skin, affecting the cells that lie deep under the skin’s surface. UVA causes aging of the skin, and long-term damage.
UVB radiation penetrates the skin’s top layer, causing sunburn, and long-term damage. Both UVA and UVB contribute to the development of skin cancer. Broad-spectrum sunscreen gives extra protection because it filters out both UVA and UVB rays. UVC radiation is absorbed in the upper atmosphere and does not reach the Earth.
A water resistance claim of two hours means the sunscreen should retain its full SPF protection for 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.
Some sunscreens can have a detrimental effect on car and other pre-painted roof and cladding products, so try to avoid contact between the hands and these surfaces.
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 unlikely to pose a health risk. Results of a 2013 Danish study seem to suggest that absorption of nanoparticles through the skin is possible, although occurs to a very low degree. Further testing is needed.
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 (sweated) off - you need to keep reapplying 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.
- Read more...Sunsmart website.
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 of NZ advises sun protection in New Zealand between September and April (especially between 10am and 4pm), or when the UVI is 3 or higher.
Also see the Sun Protection Alert (SPA) on the MetService website or in the weather section of your daily newspaper. The Sun Protection Alert includes local real time advice.
- Literature review on the safety of titanium dioxide and zinc oxide nanoparticles in sunscreens. The Australian Therapeutic Goods Administration. Version 1.0, August 2013
- Dermal absorption of nanomaterials. Danish Environmental Protection Agency, 2013