by TEANU TEJASSWINI, Masters in Cosmeceutics
Hello, gorgeous skin siders!
Our dermatologists and Aestheticians have always been advising us to regularly wear sunscreen to protect our skin from premature ageing without thinking about it much. But have you ever thought about whether your sunscreen is giving you full protection? As aestheticians, we are trained and educated to be adept on the topic of sun protection. The FDA is changing their regulations on product labelling because “SPF” was considered an unreliable measure of protection. So why don’t we try to dabble on one of the most important topics of skincare — Sun Protection.
First up is SPF.
SPF stands for sun protection factor. The number associated with the SPF is the number of times longer than you will be protected from burning than you would be without sunscreen. For example, if you usually get a sunburn in 10 minutes when outside unprotected, you should not burn for 150 minutes if you are wearing an SPF15 product. Of course, this will vary depending on your Fitzpatrick Skin type. The important thing to note is that this only refers to your protection time from UVB rays, with no specific expectation for your protection level from UVA rays.
Ok – so what’s the difference between UVB & UVA rays and why should you care?
From the above picture, the basic difference between UVA and UVB rays of the sun is seen. To know more in detail about the UV-Radiations of sun and good and bad effects.
SPF – SUN PROTECTION FACTOR
SPF, or Sun Protection Factor, is a measure of how well a sunscreen will protect skin from UVB rays, the kind of radiation that causes sunburn, damages skin, and can contribute to skin cancer.
For best protection, experts recommend using a minimum SPF sunscreen of 15, applying the proper amount (2mg/cm2 of skin, or about one ounce for full body coverage), and reapplying every 2 hours.
Most people under-apply sunscreens, using ¼ to ½ the amount required. Using half the required amount of sunscreen only provides the square root of the SPF. So, a half application of an SPF 30 sunscreen only provides an effective SPF of 5.5!
The SPF (Sun Protection Factor) scale is not linear:
SPF 15 blocks 93% of UVB rays
SPF 30 blocks 97% of UVB rays
SPF 50 blocks 98% of UVB rays
So, one way of looking at this is that SPF 30 sunscreen only gives you 4% more protection than SPF 15 sunscreen.
Or, another way of looking at it is:
SPF 15 (93% protection) allows 7 out of 100 photons through
SPF 30 (97% protection) allows 3 out of 100 photons through.
So, while you may not be doubling your level of protection, an SPF 30 will block half the radiation that an SPF 15 would let through to your skin.
How SPF Is Determined?
The SPF number is determined through indoor experiments, by exposing human subjects to a light spectrum that’s meant to mimic the noontime sun—when the sun’s rays are at their most intense. Some subjects wear Sunscreen and others do not. The amount of light that induces redness in sunscreen-protected skin, divided by the amount of light that induces redness in unprotected skin is the SPF.
What does the SPF Number Mean?
A higher SPF doesn’t indicate superior sun protection—it indicates that you will remain protected in the sun for a longer amount of time. For example, an SPF 2 protects your skin just as effectively as an SPF 30. However, an SPF 2 will need to be applied more frequently. To be safe, no matter what SPF you choose, it’s best to reapply Sunscreen at least every two hours, as well as after swimming or sweating. The American Academy of Dermatology recommends the daily application of SPF 30 to all exposed skin.
Measurements of protection
Sun protection factor and labelling
The efficacy of sunscreen is usually expressed by the sun protection factor (SPF), which is defined as the UV energy required to produce a minimal erythemal dose (MED) in protected skin, divided by the UV energy required to produce a MED in unprotected skin (equation 1):
The minimal erythemal dose (MED) is defined as the lowest time interval or dosage of UV light irradiation sufficient to produce minimal, perceptible erythema on unprotected skin. The higher the SPF, the more effective is the product in preventing sunburn
Calculations to determine UV protection factors as defined by the COLIPA standard and other regulatory agencies involve measurement of the percent transmission of a sunscreen lotion sample across the UV spectrum weighted by the erythemal weighting factors at different wavelengths.
The in vitro SPF’s were determined according to the method described. The observed absorbance values at 5 nm intervals (290-320 nm) were calculated by using the formula
where CF = correction factor (10), EE (λ) = erythmogenic effect of radiation with wavelength λ, Abs (λ) = spectrophotometric absorbance values at wavelength λ. The values of EE × I are constants.
Broad-Spectrum Sun Protection
The SPF measures only protection against the sun’s ultraviolet B rays, which are called UVB for short. Initially, UVB rays were thought to be the only UV rays to worry about, since they are shorter in length and cause sunburn. However, it became understood later that UVA rays also pose risks. They age the skin and contribute to skin cancer. SPF alone does not protect against UVA rays, so to get the best sun protection possible, look for sunscreen or sunblock that provides both UVA and UVB protection—it should say “broad spectrum” or “full-spectrum” on the label and it should have an SPF of at least 30.
How to choose the correct SPF required for our skin?
The protective efficacy of sunscreen against UVB is expressed as the SPF.
The SPF is a number representing the ratio of the time required for given irradiation to produce minimal perceptible erythema (MED: minimum erythemal dose, the UVR dose necessary to produce the minimal sunburn or minimal perceptible erythema 16 to 24 h after exposure) in sunscreen-protected skin to the time required in unprotected skin.
Depending upon the skin type and tanning history, individuals are classified as-
I. Always burns, never tans
II. Always burns, tans minimally
III.Burns moderately tans gradually to a shade of light brown
IV. Burns minimally, always tans well
V. Barely burns, tans profusely
VI. Never burns, skin becomes deeply pigmented
The UV- dose/time is used to calculate the SPF using:
SPF = MED protected skin/ MED Unprotected skin
MED protected skin- minimum erythemal dose for protected skin after application of 2mg/ cm2 or 2ul/cm2 of the final formulation of the sunscreen product
MED unprotected skin-minimum erythemal dose for unprotected skin, i.e. Skin with no sunscreen
The larger the SPF, the greater the sun protection.
The OTC panel proposed that all sunscreen products should be rated depending upon the degree of protection (rating numbers to range from 2-8).
Rating of 8 provided maximum protection for individuals who always burn and never tan while a product having a rating of 2 would be suitable for those who never burn but tan profusely.
SKIN TYPE | SPF |
I | 8 or more |
II | 6-7 |
III | 4-5 |
IV | 2-3 |
V | 2 |
VI | Not -Indicated |
5 Product category designations(PCD):
PCD 1- Minimal Sun protection product
SPF:2-4
Least protection and permits sun tanning
PCD2- Moderate sun protection product
SPF: 4-6
Moderate protection from sun- burning, permits some tanning
PCD3- Extra sun protection product
SPF: 6-8
Extra protection from sun- burning, permits some tanning
PCD 4- Maximal sun protection product
SPF: 8-15
Maximal protection from sunburning, permits little or no tanning
PCD5- Ultra sun protection product
SPF: 15 or more
Greater protection from sunburning permits no tanning.
WHAT IS THE DIFFERENCE BETWEEN SPF 15, 30 AND 50+?
The difference between SPF levels is much smaller than people realise.
Most consumers believe that SPF 30 offers TWICE the level of UVB protection than SPF 15. This is a myth!
In fact, the difference in UVB protection between SPF 15 and 30 is only an additional 3.4%. Further still, the difference between SPF 30 and SPF 50+ is only 1.6% more UVB protection!
Check out this table below to see the real differences between SPF ratings…
Why not use a really high Sun Protection Factor? Sunscreens with really high SPF’s, such as SPF 75 or SPF 100, do not offer significantly greater protection than SPF 30 and mislead people into thinking they have more protection than they actually do. Additionally, in order to have broad-spectrum protection, the UVA protection should be at least 1/3 of the UVB protection. High SPF sunscreens usually offer far greater UVB than UVA protection, thus offering a false sense of full protection.
For more Sunscreen related topics, follow our Blog post regularly.
Note: The content is 100% owned by the website owner and the blog writer. Many standard books and journal references are used in making this article.
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