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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. 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.

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 the earth’s surface
  • Its intensity varies by season, location, and time of day but in the summer months it is most intense between 10 am and 4 pm
  • At high altitudes and surfaces such as snow and ice, up to 80% of UVB rays are reflected so they hit the skin twice
  • The 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 relatively 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 an 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 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 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, 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 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 LabelMean SPFLabel SPFBroad Spectrum Claim
Low protection ≥4 – <15 4
6
8
10		 UVA-PF must be at least 1/3 of the labelled SPF (ie, SPF/UVA = <3)

And

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.

  • The European Commission does not allow labelling of sunscreen products with SPF <6 but all products with SPF ≥6 can be labelled as “Broad Spectrum” if their UVA-PF is at least 1/3 of the labelled SPF and their critical wavelength is at least 370nm.
  • The Australian/New Zealand Standard states that products must have a minimum SPF of 8 and have a UVA-PF of at least 1/3 of the labelled SPF before it can be labelled as “Broad Spectrum”. While it is optional for products with SPF between 8 and 30 to meet the requirements for broad spectrum, sunscreens with SPF ≥30 must have a UVA-PF of at least 1/3 of the labelled SPF and be labelled “Broad Spectrum”. The claim of a broad spectrum cover can only be made for products with an SPF of 50+.
  • The United States FDA regulations require a minimum critical wavelength of 370 nm in sunscreen formulations before they can be labelled “Broad Spectrum”. Products that are not broad spectrum or that are broad spectrum with SPF values between 2 and 14 must be labelled with a warning “Skin Cancer/Skin Aging Alert: …….” Sunscreen products that protect against both UVB and UVA radiation must be labelled “Broad Spectrum SPF 15 (or higher)” on the front.

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:

  • The term “waterproof” is misleading and not permitted as sunscreens will wash off when immersed in water. Claims of “water resistant” are permitted. These products should also show the amount of time you can expect to get the declared SPF level of protection while swimming or sweating, e.g. SPF 15 – Water resistant 40 min.
  • The term “sunblock” is misleading and not permitted because it may be interpreted to mean that 100% of the sunburning radiation is blocked. No sunscreen offers 100% protection.
  • The term “sweatproof” is misleading and not permitted.

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