No sunscreen will completely shield you from the effects of ultraviolet radiation (UVR). You can still burn, especially if you have sensitive skin. Sunscreen use should not be the only or even the primary line of protection against the sun. It should be used with other sun safety behaviours, including covering up and seeking shade.
The protection a sunscreen offers is affected by:
No matter how high the SPF rating, no sunscreen can block out all UVR. All sunscreens are filters allowing some UVR through to the skin. The higher the SPF, the smaller the amount of UVR that gets through. The longer the time spent in the sun, the more the UVR accumulates until enough UVR is absorbed to cause burning. Sunscreen’s protectiveness is not affected by the length of time it has been on the skin, but it is affected by ‘wear and tear’ over time. Even if you’re not very active, sunscreen can rub off gradually and, therefore, needs to be re-applied regularly to top it up. This applies particularly to children because of their active lifestyle.
SPF is a rating of what percentage of UV rays the sunscreen protects you from. For example: SPF 30+ allows one in every 30 rays in, offering 97% protection. The higher the SPF, the more UV rays are filtered and the greater the protection. Because of the number of factors involved, (eg time of the year, time of day and skin type) the SPF is not precise, but gives a general guide to sun protection.
The highest rating a sunscreen can claim is SPF50+ broad spectrum under the Australia/NZ AS/NZS2604 sunscreen standard.
A broad spectrum sunscreen gives extra protection because it screens out much of the UVA shorter wave length radiation as well as UVB.
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 re-apply sunscreen after any water sports.
Apply sunscreen 15 minutes before sun exposure to allow it time to dry and be absorbed into the skin. Spread it on to exposed skin thickly and evenly. To cover your entire body well you'd ideally use 35mls which is 7 teaspoons. If it’s put on too thinly the protection is lessened and it won’t work as well.
Sunscreens need re-applying to remain protective. However, re-applying sunscreen does not reduce UVR already received.
UVR builds up and can damage the skin even when you’re wearing a sunscreen and before burning is visible. Reduce your daily sun exposure as much as possible and in particular avoid the sun (even if using a sunscreen) between 10am – 4pm during daylight saving months. Sunscreens should not be used to increase the amount of time spent in the sun.
Sunscreen slows down further UVR accumulation and if burning has already occurred, it will only lessen the severity of further burning. Re-apply sunscreen every hour or more if you are swimming or sweating a lot.