What happens when you put product w/ SPF on top of another?
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free skin care · Thu Apr 09, 2009 2:10 pm

I know you don't get to add the SPF number and increase your sun protection level by layering one SPF product on top of another one with SPF, but what if you put moisturizer with SPF 30 on and layer sunscreen with SPF 20 on top of it? Would the top layer take precedence over the bottom? How does that work? Any idea?

free skin care · Thu Apr 09, 2009 9:10 pm

Don't quote me on this but I thought it's the SPF of the top layer you are using - SPF 30 moisturizer and then apply a foundation with SPF 15 - you're getting the benefit of the 15.

free skin care · Fri Apr 10, 2009 3:27 am

WHAT????

OK.. I did a google search and found this. I've never heard of this website before, so I don't know how much of an authority on sunscreen this guy is. But the reasoning seems to be sound..

Quote:

Question
Dear Pierre,

I read some of your replies in the Q&A sections and I must say that you are such an expert on skincare in the internet. I wish I had found your beauty box much earlier.

I really need your help this time.

(1) I am a devoted user of sunscreens. The other day, I read an article saying that "if you're using an SPF 15 moisturizer under an SPF 8 foundation, the protection you end up with may be about SPF 12 due to dilution". If someone uses a moisturizer (without SPF) and an SPF 20 sunscreens, does it end up to be only SPF 10???????

(2) What is the sequence of applying physical and chemical sunscreens? Should a physical sunscreen be applied under or over a regular chemical sunscreen?

(3) As regards maximization of UVA protection, will the sequence of layering in (2) be different if chemical sunscreens of Parsol 1789 is used together with another physical sunscreens?

Please help! The hot summer is here already.

Thanks & regards,

Kim

(submitted by alias: KIM)

Answer
Yes, that's right if you apply both on top of one another immediately without waiting for one to dry up a little - that's quite a close approximate. That's because the amount of concentration of the anti UV ingredients in the cream is the primary determinant of the SPF value. So when you mix up one with SPF 15 and 8, you get the average of SPF 12.

Example:
if you have a gram of sugar mixed in 50 grams of water in one cup, and another 3 grams of sugar mixed in another 50 grams of a separate cup. Now each cup will have different degree of
sweetness, the latter cup being sweeter. If you now mix the two cups of water, they will now be 4 grams of sugar in 100 grams of water, or 2 grams of sugar in 50 grams of water. And 2 grams of sugar is exactly the average of 1gm + 3 gms.

So, the sweetness now is between the 1st cup and 2nd cup.

If you apply one over another immediately when they are both still liquid, and mixed them up on your skin, there isn't going to be much of a difference for which one to be applied first.

But if you apply the chemical sunscreen first, and wait a while for it to dry up, before applying the physical sunscreen, then this is preferred. The chemical sunscreen works by absorbing the UV rays, to prevent them from penetration, but by absorbing the UV rays, the rays are accumulated and left on the skin surface. This can be harmful over time. The physical sunscreen works by reflecting the UV rays, thus without retaining the rays on the skin surface.

So, it is better to reflect off the UV rays on first contact with the skin, rather than to allow the rays first to be absorbed and reatined on the skin surface, in which case the inner layer will not be able to effectively reflect the rays.

The above suggestion is presumed that the person is not sensitive to chemical sunscreens. The higher SPF value in a chemicl sunscreen, the higher risk of its sensitizing effect on skin, which can cause redness and swelling.

It is better and safer to use a lower physical SPF cream, and wipe off and apply more often, than applying a high chemical SPF cream and left on the skin for several hours of exposure to the sun. It is reported that the UV rays absorbed and retained on the skin for a long period of time can lead to skin cancer too.

Hope the above helps.

http://www.pierrechenxu-intl.com/spf_us.lasso?Referrer=

free skin care · Fri Apr 10, 2009 8:01 am

That doesn't seem right...
I've always heard that if you put an SPF of 15 on top of SPF 25 you don't get an extra benefit of SPF 40 - whatever the highest SPF is, that is the SPF protection you have. I don't know though...

free skin care · Fri Apr 10, 2009 1:50 pm

Quote:

[It is better and safer to use a lower physical SPF cream, and wipe off and apply more often, than applying a high chemical SPF cream and left on the skin for several hours of exposure to the sun. It is reported that the UV rays absorbed and retained on the skin for a long period of time can lead to skin cancer too.]

I don't see how this can be right. UVA rays aren't "retained" and captured somehow on the skin. I note that the item says "it is reported" without saying by whom and in what journal. I tried a quick PubMed search on it and came up empty. Apparently no such published study exists.

I believe that what is true is that chemical sunscreens undergo chemical change when in contact with UV light, which is why they degrade in effectiveness with light exposure. I know there is also concern about the effects of the chemically changed post-UV exposed substances. But I haven't seen any peer reviewed research linking them to cancer. Perhaps others can link to studies...

free skin care · Sat Apr 11, 2009 8:31 am

Bira wrote:

I know you don't get to add the SPF number and increase your sun protection level by layering one SPF product on top of another one with SPF, but what if you put moisturizer with SPF 30 on and layer sunscreen with SPF 20 on top of it? Would the top layer take precedence over the bottom? How does that work? Any idea?

from my knowledge ,should be spf 30 on the skin for prodection.

free skin care · Sat Apr 11, 2009 12:34 pm

Katsey, I think that passage was saying exactly what you meant. What I understood from that long quote was that when layering sunscreens of different SPFs, the coverage you get at the end is an average of the 2 sunscreens, not the lowest of the two, and definitely not the sum to the 2.

Flitcraft, I apologize for copying that Q/A in its entirety, when I was only concerned with the top part regarding layering of sunscreens and the resulting SPF coverage. As to the physical/chemical issue, I'm sorry I don't know too much about it and am not savvy enough of a researcher to find more validated reports... Perhaps some of the more knowledgable members here would likt to help us out...? TIA!

Sat Apr 11, 2009 3:56 pm

if you put a spf30 over a spf15, you still have spf30.
if you put spf15 over spf30, you still have spf30

Sat Apr 11, 2009 3:57 pm

and I forgot to mention.
you probably would have blocked pores and pimples

free skin care · Fri Jul 30, 2010 1:34 pm

I know this thread is from last year but layering physical over chemical sunscreens intrigued me.

"If you apply one over another immediately when they are both still liquid, and mixed them up on your skin, there isn't going to be much of a difference for which one to be applied first.

But if you apply the chemical sunscreen first, and wait a while for it to dry up, before applying the physical sunscreen, then this is preferred. The chemical sunscreen works by absorbing the UV rays, to prevent them from penetration, but by absorbing the UV rays, the rays are accumulated and left on the skin surface. This can be harmful over time. The physical sunscreen works by reflecting the UV rays, thus without retaining the rays on the skin surface.

So, it is better to reflect off the UV rays on first contact with the skin, rather than to allow the rays first to be absorbed and reatined on the skin surface, in which case the inner layer will not be able to effectively reflect the rays.

The above suggestion is presumed that the person is not sensitive to chemical sunscreens. The higher SPF value in a chemicl sunscreen, the higher risk of its sensitizing effect on skin, which can cause redness and swelling. "

Does anyone do this? Photostability aside, is it safe? It makes sense.

free skin care · Fri Jul 30, 2010 1:50 pm

I just found this from another thread, posted by SeptemberGirl- thank you! Smile

"Top dermatologist Dr Leslie Baumann recommends a double layer of sunscreen, first a chemical sunscreen, and then a physical sunscreen on top, when spending many hours outdoors.

Quote:

4. If I am going to spend any significant time in the sun, though, a moisturizer with SPF is not enough. I add a chemical sunscreen like La Roche-Posay Anthelios SPF15 (if I'm lucky, I might even have some of the SPF50+ version that's only available abroad), followed by Blue Lizard Australian Suncream for sensitive skin. (The Blue Lizard is a physical sunscreen - that is, it contains zinc oxide and titanium oxide to reflect light - and may appear white for the first few minutes after it's applied). Using both a chemical and a physical sunscreen might seem like overkill, but it's absolutely the best way to protect skin in sunny environments.

http://health.yahoo.com/experts/skintype/11397/a-daily-skin-care-routine/ "

free skin care · Fri Jul 30, 2010 2:45 pm

I have been researching and Titanium Dioxide has a negative effect on Avobenzone, so layering LRP with a physical sunscreen seems out of the question. However, Lancome has some sunscreens formulated with mexoryl sx and xl only- so I will look into that.

I think layering sunscreen in the summer may be a great alternative for me. I can't tolerate high portions of physical sunscreens.

Sun Aug 01, 2010 4:20 pm

Both of them spf products will work but separately. If u put on spf 30 and then spf 15 your skin will be protected by the maximum power of spf 30 only because its stronger.

Mon Aug 02, 2010 5:37 am

Hi there,

This is my first post, although I've been obsessively following assorted forums for 4 years now Very Happy

I, too, have recently been sifting through all the info out there about most effective and safe options for broad spectrum sun protection. After just a cursory exploration, it is very clear to me that with a few exceptions, (mostly European imports)chemical sunscreens are very problematic on so many health fronts; I'm surprised more people aren't more aware of the dangers.

"...there is plenty of evidence that numerous chemical UV filters have the potential to increase cancer-causing free radicals (6). Others may have possible estrogenic and other adverse effects, and another is actually systemically absorbed and excreted in urine at a much higher rate than any other sunscreen filter ..."

check the following link to the complete, very revealing article, exposing significant risks we should all be aware of.

See the article entitled uv damage, the right way to protect yourself, on the bulkactives . com website (I can't post the actual link, I've been informed, since I am a new member..)

In addition to helpful cautionary info, this articles also provides useful, positive recommendations. As you probably have guessed, most of these revolve around a select group of physical sunscreen blocking ingredients.

I stumbled upon this info while reading the ingredient list in AlphaDerma CE, which (up until then) appeared to be a dream product for my concerns of firmness, wrinkles, etc. What I found were two sunscreen listings: Octyl Methoxycinnamate and Oxybenzone (the ingredients listed in third and sixth place!!!) Oxybenzone is becoming more and more universally acknowledged as very problematic!! I'm really bummed because I was just on the verge of ordering the ADCE, and had found a fantastic price (88.99 for 4 oz/free shipping...oh well)

Sorry for the very boring post, but I think if you read the article, you will be enlightened and quite a bit alarmed. Chances are many of the UVA/UVB products you use contain highly questionable ingredients.

I'm sure most of you are already familiar with EWG . ORG and it's EWG 2010 Sunscreen Guide. If not, you should check it out.

It is perhaps OVERLY cautious and critical, but still very helpful in narrowing down the most effect and least risky products.

Now that my hopes are dashed...does anyone have an alternative to AlphaDerma CE, without the chemical sunscreen? It seemed like a perfect addition to my regimen of retin a/renova at night, and either skinceuticals or obagi 15 or 20% c serum in the daytime, topped with my new favorite sunblock, EltaMD 41, tinted (it's a top rated, and does double duty as foundation replacement...)

I'm mostly happy, but am now needing to more aggressively target the ol' neck, sagging and lost of elasticity/crepiness, that is. Same with upper eyelid area, though I've been gradually trying to acclimate to small amounts of .025 renova...

Thanks

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