DermNet provides Google Translate, a free machine translation service. Note that this may not provide an exact translation in all languages
Author: Vanessa Ngan, Staff Writer, 2012.
Sunlight generates warmth (infra-red) that we can feel, visible light (that our eyes can see in daylight) and ultraviolet light (UVL) which we cannot see or feel but which can penetrate our skin. The UV light is grouped as UVA, UVB and UVC. The shorter wavelength UVC rays are absorbed by the ozone layer and do not reach earth. However, both UVA and UVB penetrate the atmosphere and play a major role in causing conditions such as sunburn, premature skin ageing, and skin cancers. To better understand how sunscreens work to help prevent these conditions we need to know more about the differences between UVA and UVB radiation.
For many years now sunscreens have been tested and rated for their SPF (Sun Protection Factor) value. The system used worldwide determines the ratio of the UV radiation dose it takes to cause a barely detectable sunburn on a person treated with a sunscreen product (coverage of 2 mg/cm2) compared to that required for untreated skin. For example, if it takes 10 minutes to burn without sunscreen and 150 minutes to burn with sunscreen, then the SPF of that sunscreen is 15 (150/10). However, SPF is mainly the measure of the sunscreen product’s ability to shield against UVB rays.
The following table compares how the skin receives a sun-burning dose of UVL without sunscreen protection, and with protection from sunscreens with different SPF values.
|SPF value||Sun-burning dose over time (%)*|
|10 mins||30 mins||150 mins|
|1 (no protection)||100%||–||–|
* assumes application of 2 mg/cm2. In reality, people do not usually apply this amount of sunscreen so the expected sun protection will not be achieved.
In recent years, due to increasing knowledge about UVA-induced skin damage, there has been much development on methods for determining UVA performance, referred to as the broad spectrum performance of a sunscreen. Currently there is no internationally agreed standard for testing and measuring UVA protection, although most countries have moved away from performing the in vivo persistent pigment darkening (PPD) method and now use in vitro PPD methods to determine the UVA Protection Factor.
|Region||Methods for testing UVA protection|
|Australia/New Zealand Standard (AS/NZS 2604:2012)||
|European Union (Commission Recommendation 22 September 2006)||
|United States of America (FDA final rules 17 June 2011)||
Due to ethical concerns about the use of in vivo testing methods, the European Commission is encouraging the sunscreen industry to increase efforts in developing in vitro testing methods for the protection against both UVB and UVA radiation.
The UVB and UVA sunscreen ratings provide the necessary information for labelling of sunscreen products so that consumers have a better understanding about which products offer the best protection. Although category and labelling descriptions vary slightly between countries, Australia/New Zealand, the European Union and the United States are closely aligned.
|Category Label||Mean SPF||Label SPF||Broad Spectrum Claim|
|Low protection||≥4 – <15||4
|UVA-PF must be at least 1/3 of the labelled SPF (ie, SPF/UVA = <3)
Critical wavelength ≥370 nm
|Medium/moderate protection||≥15 – <30||15
|High protection||≥30 – <60||30
|Very high protection||≥60||50+|
The following list shows the main differences between the standards for the regions.
All regions are in agreement that sunscreen products that provide both UVB and UVA protection are labelled with the SPF value and the words “Broad Spectrum”. The broad spectrum statement and SPF value together provide a measure of both UVB and UVA protection, with increasing SPF values indicating a proportional increase in UVA protection.
In addition to the labelling requirements of SPF value and broad spectrum statement, the latest standards no longer allow the following claims to be made on sunscreen labels:
See the DermNet NZ bookstore.
© 2022 DermNet New Zealand Trust.
DermNet NZ does not provide an online consultation service. If you have any concerns with your skin or its treatment, see a dermatologist for advice.