Introduction
Have you ever sought to understand the distinctions between an SPF 30 and SPF 50 sunscreen? What is the relevance of broad spectrum, and how are SPF tests conducted? Can you really trust them? Ultraviolet (UV) rays and sun-induced damage play a significant role in various skin health issues, such as skin cancer, premature aging, and hyperpigmentation. UV rays encompass UVA, UVB, and HEV, each having distinct implications for skin health. It is crucial to use sun protection that effectively defends against these different types of UV radiation.
We will examine SPF testing, how SPF values are calculated, the limitations of these SPF ratings, and what you need to know to choose a sunscreen that offers comprehensive protection against UVA and UVB rays.
Understanding SPF Ratings
SPF: Sun Protection Factor
The SPF (Sun Protection Factor), created in 1974 by Dr. Franz Greiter, measures a sunscreen's ability to protect the skin from sunburn caused by UVB rays. A handy mnemonic reminds us that UVB rays cause Burns.
How SPF is Measured:
SPF tests can be conducted either in vivo (on human participants) or in vitro (in a laboratory). Generally, in vivo SPF tests (according to the ISO 24444 standard) are preferred, as laboratory environments struggle to replicate human variables such as skin texture and absorption, which influence test results. In practice, approximately 2 mg per square centimeter of sunscreen is applied to the study participants' skin. Then, the skin area is exposed to UV rays. The SPF value indicates the time required for the skin patch to develop an erythema (redness), whether with or without the application of sunscreen. For example, if your skin burns in 10 minutes without sunscreen but takes 5 hours (300 minutes) to burn with sunscreen, then the sunscreen allows you to be exposed to UV rays 30 times longer and has an SPF value of 30.
- SPF15: Filters approximately 93% of UVB rays.
- SPF30: Filters approximately 97% of UVB rays.
- SPF50: Filters approximately 98% of UVB rays.
However, no sunscreen blocks UVB rays 100%, hence the importance of regular reapplication. Furthermore, the effects of UVA rays are not immediately visible and cannot be measured by SPF tests. SPF values are not useful when looking for UVA protection, which is why it is important to look for broad-spectrum sunscreens.
The Concept of "Broad Spectrum"
Protection Against UVA and UVB
The "Broad Spectrum" label means that the sunscreen offers protection against both types of ultraviolet rays: UVA and UVB. UVA rays contribute to skin aging, while UVB rays cause sunburn (solar erythema) and are associated with skin cancer. A handy mnemonic reminds us that UVA rays are a factor in Aging. The Broad Spectrum claim is important to consider when choosing a sunscreen, as UVA rays account for 95% of solar radiation and cause photodamage that can lead to skin aging and cancer. Be sure to choose a broad-spectrum sunscreen for complete protection.
The PA+++ Rating
Protection Against UVA
In addition to the in vivo SPF tests performed to determine UVB protection, additional UVA tests must be conducted based on Persistent Pigment Darkening (PPD). Unlike SPF, which measures the minimal erythemal dose, here we measure the dose of UVA required to cause persistent pigmentation, i.e., pigmentation due to the oxidation of melanin that persists 2 hours after the end of UVA exposure (which is very different from tanning).
UVA protection measurement varies from one country to another. European regulations require that anti-UVA protection (PPD) be at least 1/3 of the SPF indicated on the labeling and must cover longer UVA rays, which corresponds to a minimum critical wavelength of 370 nm to be eligible for broad-spectrum certification. The PA+++ rating is used in Asia to evaluate protection against UVA rays. The more "+" signs in the rating, the higher the UVA protection. UVA rays contribute to premature skin aging.
- PA+: Low protection (PPD of 2 to 4)
- PA++: Moderate protection (PPD of 4 to 8)
- PA+++: High protection (PPD of 8 to 16)
- PA++++: Very high protection (PPD>16)
Conclusion
Choosing the right sunscreen is essential for protecting your skin from the harmful effects of the sun, especially in urban environments. It is important to understand that even an SPF 25 offers protection against 96% of UVA and UVB rays, and that an SPF 50 only adds 1 to 2% more protection. For effective protection throughout the day, regular reapplication is essential, and an SPF 25 is ideal because its texture encourages reapplication for optimal results. More importantly, consider the PA+++ rating for comprehensive defense against UVA rays and ultra-broad-spectrum protection against visible blue light and urban pollution.
TRUE FILTER™ Urban Protective Mist: a small step for great protection
Complete ultra-broad-spectrum UVB/UVA protection
TRUE FILTER™ offers patented ultra-broad-spectrum protection against UVA, UVB, and blue light (HEV), surpassing that of conventional sunscreens. With an SPF 25, this mist filters 96% of UVB rays, focusing on the part of the light spectrum that is most influential in photoaging: UVA rays.
Reduction of oxidative stress and PA+++ rating
Featuring a PA+++ rating, TRUE FILTER™ prioritizes deep protection against photoaging, the main cause of 80% of skin aging. This mist offers integral defense rather than targeting specific symptoms.
Advanced Protection against Blue Light (HEV) and Pollution
TRUE FILTER™’s protection extends to damage from blue light (HEV) and air pollution, a major contributor to skin aging. This extent of protection is unparalleled, exceeding photoprotective products widely considered "broad spectrum" or PA-rated.
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Bibliography
- A. Green, et al. “Sunscreen and prevention of skin aging: a randomized trial” Ann Intern Med. 2013 Jun 4;158(11):781-90. https://pubmed.ncbi.nlm.nih.gov/23732711/
- M. R. lannacone, M. C. B. Hugues, A. C. Green “Effects of sunscreen on skin cancer and photoaging” Photodermatol Photoimmunol Photomed. 2014 Apr-Jun;30(2-3):55-61. https://pubmed.ncbi.nlm.nih.gov/24417448/
