How Much SPF Do You Need in Your Sunscreen?
Some great articles on IMBB get lost amongst the horde of articles here. Months ago, SRV wrote an article on ‘Ingredients in Cosmetics and Beauty Products: The Real Story‘ which was an eye opener for me and really got me thinking. One big question that came into my mind at that time was ‘How do these companies decide SPF of their product?’ to put on the labels of their product? Or more importantly, since SRV said that most India companies stick these SPF numbers on their products randomly, what IS the correct procedure for determining SPF in cosmetic products or sunscreen? Also, what would be the correct sunscreen to pick?
To avoid the crime of repeating myself, I would request the readers to read my article on sunscreen first to know some facts about sunscreens. Also read the description of Fitzpatrick Skin Type to understand the basic skin type used by scientists/ dermatologis in determining the spf.
For continuity, I am posting the basic information about SPF that I wrote earlier:
What is SPF?
Sun Protection Factor (SPF) is a measure of a sunscreen ability to protect against the UVB rays, the rays that cause sunburn. The SPF is the amount of UV radiation required to cause sunburn on skin with the sunscreen on, relative to the amount required without the sunscreen. So, wearing a sunscreen with SPF 15, your skin will not burn until it has been exposed to 15 times the amount of solar energy that would normally cause it to burn. That means that it has cut down the radiation to 1/15 of the original or blocked 14/15 or 93% of UVB rays. Using the same logic SPF 30 stops (1 – 1/30) or 97 percent of UVB rays. If you go as high as SPF 50 it stops 98 percent of UVB rays. But no matter how high the SPF, it is only a protection against UVB, and NOT the UVA.
How to Determine SPF of a Product/ Sunscreen?
To calculate SPF, scientists gather 20 human volunteers who are especially susceptible to sunburn. According to FDA guidelines, volunteers must have a skin type of I, II, or III on the Fitzpatrick phototyping scale. Using a device called a “solar simulator,” experimenters irradiate a small patch of skin on each subject and then record the UV dose required to produce mild redness (in scientific parlance, the “minimal erythematic dose”). After applying a thick layer of sunscreen, the experimenters repeat the test. Then they divide the MED needed to redden the protected skin by the MED needed to redden bare skin. The result, rounded down to the nearest five, is the SPF.
How Much SPF Do You Need in Your Sunscreen?
Very simple if you think of it. All you need to know is your Fitzpatrick skin type. Your Fitzpatrick skin type determines how long you can stay in the sun without any sunscreen. Here is a rough guideline on how long can you stay out in the sun without sunscreen-
Skin Type 1: 20 minutes
Skin Type 2: 30 minutes
Skin Type 3: 40 minutes
Skin Type 4: 60- 90
Skin Type 5: About 120 minutes
Skin Type 6: For many many hours
Now all you need to know is how long are you going to stay out in the sun for a particular day and divide it by the number of minutes you can stay in the sun without the sunscreen for your skin type and you get your SPF number. So for example, if you are skin type 2 and you need 10 hours or 600 minutes of protection in the sun you need an SPF of 300/ 30 = 10. If you need 24 hours (1440 minutes) of protection for skin type 2, you need an SPF of 1440/30 = 48 or around 50.
Conversely, if you are skin type 1 and you are using an SPF of 15, you can stay out in the sun for 20 x 15 = 300 minutes (5 hours). After that you would need to reapply your sunscreen if you want to stay out in the sun further.
Remember that these figures would not work if you are going for swimming or such similar activities. If you go for a swim, remember to apply the sunscreen again after you have toweled off.
Sun Protection through Clothing
T-shirts and most summer weight fabrics allow as much as 50% of harmful UV rays through to your skin when dry and 60 to 70% when wet. T-Shirts provide only moderate protection. In general, heavier, darker, more tightly woven fabrics like denim offer more sun protection than lightweight fabrics like linen and lace. Hats that cover the head and neck offer great protection. Wide rims that go all the way around are the best. Open mesh baseball caps and open-weave straw hats don’t offer good sun protection because they allow UV rays in.
What is the Best Sunscreen Available?
As I mentioned in my earlier article, most sunscreens provide protection against the UVB rays of the sun and not the UVA rays. UVA radiation reaches deeper into the skin and contributes to wrinkles and skin cancer risk. Nearly all (95%) of the UV radiation that we are exposed to is UVA radiation. The best UVA protection is provided by products that contain avobenzone, and ecamsule. But these compounds quickly go photodegradation in the sun, breaking down and losing effectiveness fast. A chemical stabilizer is included in some sunscreens containing avobenzone to slow its breakdown – examples include formulations containing Helioplex and AvoTriplex.
So if you are looking for a good sunscreen for both UVA and UVB protection look for the following products- avobenzone, meroxyl, ecamsule, helioplex, micronic zinc oxides.
Some Sunscreen Suggestion
Hope this article helps you understand SPF and sunscreen better. 🙂