Sunscreen testing and classification

Author: Vanessa Ngan, Staff Writer, 2012.

Introduction

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. 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 aging of the skin, 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.

UVBUVA
  • Wavelength 290-320nm
  • Most are intercepted by the ozone layer but with the depletion of the ozone layer more UVB rays are now reaching earth’s surface
  • Its intensity varies by season, location, and time of day but in the summer months it is most intense between 10am and 4pm
  • At high altitudes and surfaces such as snow and ice, up to 80% of UVB rays are reflected back so they hit the skin twice
  • Main cause of skin reddening and sunburn and damages the upper epidermal layers of skin
  • 20-30 minutes of UVB exposure a day helps the skin to produce bone-building vitamin D3
  • Suppresses skin immune function
  • Wavelength 320-400nm
  • UVA I 340-400nm
  • UVA II 320-340nm
  • Accounts for up to 95% of UVL reaching the earth’s surface
  • Present with relative equal intensity throughout the year
  • Can penetrate clouds and glass
  • Penetrates the skin more deeply than UVB rays and damages skin cells in the basal layer of the epidermis
  • Responsible for causing a deep tan which is really injury to the skin’s DNA
  • Contributes to and may even start the development of skin cancers
  • Suppresses skin immune function

How are sunscreens rated?

UVB rating

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 a sunscreen and 150 minutes to burn with a 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 valueSun-burning dose over time (%)*
10 mins 30 mins 150 mins
1 (no protection) 100%
15 6.6% 20% 100%
30 3.3% 10% 50%
50 2% 6% 30%

* 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.

UVA rating

In recent years, due to increasing knowledge about UVA-induced skin damage, there has been much development on methods for determining UVA performance. This is also 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.

RegionMethods for testing UVA protection
Australia/New Zealand Standard (AS/NZS 2604:2012)
  • UVA-PF – using the method as defined by the ISO standard ISO 24443:2012 Determination of sunscreen UVA photoprotection in vitro; and
  • MPF380 – Monochromatic Protection Factor calculated at 380nm
European Union (Commission Recommendation 22 September 2006)
  • UVA-PF using in vitro PPD method as modified by the French health agency Afssaps. Or an equivalent degree of protection obtained with any in vitro method; and
  • Critical wavelength testing method to achieve a critical wavelength of 370 nm
United States of America (FDA final rules 17 June 2011)
  • Critical wavelength testing method to achieve a critical wavelength of 370 nm

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.

What do sunscreen ratings mean?

The UVB and UVA sunscreen ratings provide the necessary information for labeling of sunscreen products so that consumers have a better understanding about which products offer the best protection. Although category and labeling descriptions vary slightly between countries, Australia/New Zealand, the European Union and the United States are closely aligned.

Category LabelMean SPFLabel SPFBroad Spectrum Claim
Low protection ≥4 – <15 4
6
8
10
UVA-PF must be at least 1/3 of the labeled SPF (i.e.: SPF/UVA = <3)

And/or

Critical wavelength ≥370 nm
Medium/moderate protection ≥15 – <30 15
20
25
High protection ≥30 – <60 30
40
50
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 labeled with the SPF value and the words “Broad Spectrum”. The broad spectrum statement and SPF value together provides a measure of both UVB and UVA protection, with increasing SPF values indicating a proportional increase in UVA protection.

In addition to the labeling requirements of SPF value and broad spectrum statement, the latest standards no longer allow the following claims to be made on sunscreen labels:

Related information

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