Have you ever wondered how many sunscreens have insanely high SPF ratings, but don’t actually contain the necessary amounts of the various UV filters to achieve such a rating?
Well, I definitely have. And more often then not, the questionable SPF ratings occur with sunscreens that utilize inorganic UV filters such as titanium dioxide (TiO2) and zinc oxide (ZnO). While I’ve certainly seen similar organic sunscreens, the disparity between the high SPF ratings and the relatively low % of UV filters is usually less with those types of sunscreens. Therefore, this post will focus primarily on inorganic sunscreens; though as you will soon see, this issue readily applies to organic ones as well.
Now, I’ve always attributed this unexplained phenomenon to the manufacturer’s ability to manipulate the vehicle, coating type, particle size, etc… to achieve such a high SPF rating. For more information on what factors can influence an inorganic UV filter’s capacity to protect against the sun, see Part III of the Sunscreen Battle. While I certainly still acknowledge that these aspects will influence a particular sunscreen’s SPF rating, there’s something that I have never considered: That a formulation’s antioxidants and anti-inflammatories can skew, exaggerate, and even mask a product’s TRUE SPF rating.
But before we get into that, we need to first understand WHAT SPF really means, and HOW it is measured.
What Does SPF Mean? How Is It Measured?
As most of you know, SPF stands for Sunburn Protection Factor. At its most basic representation, SPF can be understood as:
Minimal Erythema Dose with Protection Skin
Minimal Erythema Dose with Unprotected Skin
Because of this, most people think that if you wear a sunscreen with an SPF of 15, you can stay in the sun 15 times longer than if you weren’t wearing any sunscreen, without burning. In theory, that statement is correct. But in reality, that statement is incomplete and therefore, inaccurate. Here’s why:
Mathematically speaking, the two minimal erythema doses (MEDs) shown above, are calculated by multiplying several summations/integrations with one another. The actual formula can be found on page 2 of this PDF. They are comprised of the Sun Spectrum, the Erythemal Action Spectrum, and the UV Transmission with 2.0 mg/cm^2 of sunscreen. (To see how much that amount actually converts to, check out this post.) In laboratory tests, all of these numbers are static, meaning that they don’t change over time. In reality however, the Sun Spectrum will change because the sun itself gives off varying amounts of UVB light; specifically, its output is similar to that of a bell curve:
Furthermore, the UV Transmission will change due to a variety of factors such as sunscreen transfer, absorption, and degradation. This is why I recommend inorganic sunscreens because they are inherently stable and do not absorb into the skin at all. And of course, application amount will definitely vary–another influence on a product’s true SPF rating.
Therefore, there’s really no point in drawing much literal meaning from that limited definition of SPF.
Another often used definition of SPF is to say that an SPF of 15 will block [1- (1/15)] x 100% = 93.33% of UVB rays, because it’s extending the MED by 15, meaning that the same small amount of UVB light gets through the sunscreen per single MED, until the skin finally burns after 15 of those (100-93.33%) = 6.67% MEDs. Like the other example, this is theoretically true. Unlike the other example however, this is also realistically true (to an extent), though many people don’t realize it. The fault lies with its interpretation and presentation. Depicted as such, most people focus on the % of UVB light blocked. Therefore, an SPF of 10 blocks 90% of UVB rays, and an SPF of 50 blocks 98%–a difference of only 8%. In reality however, the difference is much more significant that it appears on paper.
Your skin has a natural protective and corrective enzymatic system that will repair UVB-induced damage. However, it can only do this at a certain rate. Furthermore, it can be overwhelmed by a sudden influx of UVB-induced damage, which results in erythema or a sunburn. Think of it like trying to pump water out of a boat that has a small hole in the floor, versus trying to do so in the middle of a hurricane.
Therefore, what’s important to note is how much UVB light is actually coming into contact with the skin at any one time. The lower the amount of direct DNA damage is present (at any one time), the more effect your skin’s reparative enzymes will have on the cumulative amount of damage. It is likely that the arbitrary SPF rating of 15 was shown to be the approximate threshold at which the skin can repair itself without too much trouble.
Therefore, it is the % of UVB light that sunscreens DON’T block or ALLOW TO HIT THE SKIN AT ANY ONE TIME, that is ultimately important.
So in some ways, the ubiquitously used (though in inaccurate) definition of “A product with an SPF of X will allow me to stay in the sun for X times longer…” has some truth to it. For example, one of the most frequently asked question is:
Q: “Isn’t SPF 30 TWICE as strong as SPF 15, since it allows me to stay in the sun TWICE as long without burning?”
A: As demonstrated above, this definition alone is too specific because it only considers time. In order to better understand the meaning of SPF, you have to evaluate the definition by action/time or RATE–specifically, the rate at which a sunscreen allows UVB light to hit the skin. With this updated and more encompassing definition, you will indeed see that SPF 30 is TWICE as strong as SPF 15!
- SPF 30 allows 100/30 = ~3.33% of UVB light to hit the skin.
- SPF 15 allows 100/15 = ~6.66% of UVB light to hit the skin.
- ~3.33% X 2 = ~6.66%.
- SPF 15 allows TWICE the amount of UVB light to hit the skin compared to SPF 30. Keep in mind that “TWICE” is a relative measurement, rather than an absolute one.
And to help the skin’s enzymes repair some of the DNA damage incurred by any UVB light that manages to get past the UV filters, are antioxidants. Okay, they sounds like good things, right? But then, why did I describe antioxidants and anti-inflammatories with a negative connotation in the title? Here’s why:
The Antioxidants and Anti-Inflammatories in Sunscreens Make the SPF Rating Appear Higher Than It Actually Is
Let’s go back to how SPF is calculated. It takes into account the Sun Spectrum, the Erythemal Action Spectrum, and the UV Transmission. As shown above, in realistic scenarios both the 1st and 3rd aspects will change over time. The 2nd aspect (Erythemal Action Spectrum) remains the same. However, with the addition of antioxidants and anti-inflammatories, this 2nd aspect will now also change over time.
Because SPF is based on how much energy it takes to trigger erythema or sunburn, antioxidants and anti-inflammatories that reduce erythema are thereby exaggerating how well the UV filters protect against UVB rays! But isn’t reducing erythema regardless of the mechanism a good thing? Well, yes and no.
Yes, in the sense that reducing erythema/redness/sunburn is good. But no, in the sense that a high SPF rating (achieved by antioxidants, anti-flammatories, and UV filters) makes people think that they are very well protected from UVB light and that the UV filters (or the active ingredients) are responsible!
In order to fully understand this subtle difference, we need to understand what happens when UVB light hits the skin.
What Happens When UVB Light Hits the Skin?
UVB light is very potent. But due to its potency, it is limited to the epidermis. Therefore, it directly damages DNA in living (epidermal) skin cells. When this happens, the DNA strand will break away from its conjugate or corresponding pair, and attach to other bases. The resulting structures become either cyclobutane pyrimidine dimers (CPD), or pyrimidine 6 to 4 photoproducts. At this point, most of the DNA damage will be repaired by enzymatic excision. However, the few that are not will then be recognized by transcription factor NF-κB, which will then activate the synthesis of a variety of regulatory and inflammatory mediators such as cytokines and matrix metalloproteinases, which then of course trigger erythema and eventually apoptosis (programmed cell death).
- UV filters (whether inorganic or organic) directly stop UVB light from coming into contact with the skin. Therefore, no direct DNA damage occurs.
- Antioxidants like green tea on the other hand, allow UV light to come into contact with the skin, meaning that they do not act like direct UV filters. They just repair any DNA damage afterwards. Keep in mind that the success rate of repair is not 100%.
- Anti-inflammatories like aloe vera are the worst, in the sense that they will reduce the erythemal reaction, without actually repairing the DNA damage.
Here’s a metaphor to understand everything:
- Your body = keratinocyte (living epidermal skin cell)
- UVB light = bullet
- Sun = gun
- Direct DNA damage = wound
- Erythema = scream (from pain)
- UV filter = ZnO = body armor
- Antioxidant = green tea = doctor
- Anti-inflammatory = aloe vera = duct tape
So you walk into a bar (no, this is the not the beginning of a joke) and someone shoots you with a gun. ZnO would acts like body armor and stop the bullet from hitting your body. Therefore, you wouldn’t scream. Green tea would act like a doctor and allow the bullet to hit your body, but then repair the wound soon afterwards. Therefore, you wouldn’t scream. Aloe vera would act like duct tape and allow the bullet to hit your body, but then muffle your mouth soon afterwards. Therefore, your scream wouldn’t be heard.
So SPF ratings are basically measured by counting the number of screams. As you can see, all three compounds (UV filters, antioxidants, and anti-inflammatories) result in no screams being heard. But the mechanisms by which they do so, are very different.
But does that mean that antioxidants and anti-inflammatories are a bad thing?
Well, obviously not. Antioxidants are meant to take care of the effects of any UVB (and UVA, but we’re just talking about UVB in this SPF-related post) light that manages to get past the UV filters; they’re the last line of defense. Anti-inflammatories are meant to reduce any redness, because let’s face it, no one likes that. And keep in mind that many anti-inflammatories are antioxidants as well. It’s just the compounds that are strictly anti-inflammatories that should be avoided after sun exposure if your goal is to repair DNA damage. But after a sunburn manifests (when the damage has already occurred and nothing can be done) anti-inflammatories will be your best friend because they reduce the inflammatory response, without significantly interfering with the healing process.
But the point of all this is to show that you need to be careful and not be fooled by sunscreens that have high SPF ratings and a mismatched amount of UV filters. Because while you think that these sunscreens will provide a lot of protection, they won’t. But you can’t tell because the visible response to direct DNA damage (erythema) has been masked.
Take this sunscreen for example: The Devita Solar Body Block SPF 30
Here’s the ingredients list:
ACTIVE INGREDIENT: Zinc oxide 19% INACTIVE INGREDIENTS: Aloe barbadensis (certified organic aloe vera gel), Water (purified), Camellia sinensis (Japanese green tea) leaf extract, Capric/caprylic triglycerides (derived from coconut oil), Glycerin (vegetable), Butyrospermum parkii (shea butter), Olea europaea (olive) oil, Lecithin phospholipid, Hyaluronic acid (vegan source), Simmondsia chinensis* (jojoba) seed oil, Squalane (olive), Panthenol (vitamin B5), Tocopherol (vitamin E), NaPCA, Rosa moschata (rose hips) oil, Centella asiatica (goto kola), Copper gluconate, Magnesium ascorbyl phosphate, Fucus vesiculosis (seaweed) extract, Allantoin, Sodium riboflavin phosphate, Chondrus crispus (Irish moss), Lavandula officinalis* (lavender) essential oil, Anthemis nobilis (chamomile) flower essential oil, Vitis vinifera* (grape) seed extract.
Note that, Devita uses uncoated ZnO particles. Now, it was documented that even at the maximally allowed concentration (25%), it was difficult for ZnO to achieve an SPF greater than 10. Uncoated ZnO at 25% also yields the same number using the BASF sunscreen simulator, which IS THE BEST TOOL THAT THE AVERAGE CONSUMER CAN USE TO MEASURE THE EFFICACY OF A SUNSCREEN. Did that really require the use of CAPS? YES! But we’ll get into its pros and cons, and how to use and understand that tool in another post.
That being said, how in the world did Devita achieve an SPF of 30 for this product? Again as I said above, while I agree that the vehicle, clumping tendencies, particle size, etc… can influence the SPF rating, I don’t believe they can influence it THAT much, at least not from SPF 10 to SPF 30, and not from this formulation! Looking at the vehicle, it’s not super sophisticated or complicated to understand. The ZnO particles (being uncoated) are suspended in the water phase AKA the aloe vera gel and water, along with several other water-soluble plant extracts such as green tea. The rest are suspended in the oil phase that is made up of the various non-fragrant plant oils and their related components such as triglycerides. Finally, to keep the two phases mixed, lecithin phospholipid acts as the primarily emulsifier. As you can see, there are no complicated cross/copolymers, acrylates, synthetic hybrids, or any of that crazy stuff with which to contend. But what IS present? A lot of green tea and aloe vera… *DUN DUN DUN* THAT’S how Devita achieved such a high SPF rating with just uncoated ZnO. How sneaky…! I’m not saying this is a bad sunscreen. But you may want think twice before bringing this to the beach.
So Should I Still Look for Antioxidants and Anti-Inflammatories in Sunscreens?
Well, the answer to that will vary depending on the individual and the product in question.
For the “Ideal Routine,” I always recommend a separate antioxidant product that’s to be applied underneath the sunscreen, because as a dedicated product, it tends to contain significantly higher %s of antioxidants. As for the sunscreen, whether or not it contains antioxidants and anti-inflammatories should be irrelevant. If it contains some, great? If not, that’s great too. In order to find out if your sunscreen provides adequate protection from the UV filters alone, use the BASF sunscreen simulator to evaluate its efficacy in terms of SPF, UVA-PF, uniformity of sun protection, and stability. Again, I’ll get into how to use and interpret this simulator in another post. As long as the UV filters alone provide adequate levels of protection, then the antioxidants and anti-inflammatories are just icing and cherries.
Similarly, for those of you who don’t have time or prefer to have combination products (sunscreen with antioxidants), use the BASF simulator to evaluate whether or not the UV filters alone provide adequate sun protection.
The two main lessons from this post should be:
- The most important thing is to reduce the total amount of UVB light hitting your skin AT ANY ONE TIME. Therefore, see SPF ratings as the % of UVB light that are allowed in, rather than the % of UVB light blocked/absorbed.
- Always use the BASF sunscreen simulator to check and see if your sunscreen provides adequate sun protection based on the UV filters alone, because non-vehicular “beneficial” ingredients like antioxidants and anti-inflammatories, can seriously skew, exaggerate, and mask a sunscreen’s true SPF rating.
***Oh and note that antioxidants and anti-inflammatories cannot skew UVA-PF/PPD/PA ratings because they cannot meaningfully prevent the immediate oxidation or darkening of existing melanin in the skin–the characteristic from which these ratings are measured.
Well, I hope this topic was as EYE-OPENING as it was for me. When I first made this connection between antioxidants and fluffed SPF ratings, I was like WHOA. MIND = BLOWN. EUREKA.
Okay, the nerd is done.