Monday, May 31, 2010

Sunscreens

Yep, it's that time of year again (at least in the Northern Hemisphere)! It's time to buy buckets of sunscreen and make sure Mr. Sun doesn't make us all red and unhappy! We definitely need to be wearing sunscreen!


There are two types of sunscreen ingredients - physical blockers and chemical blockers. The physical blockers are titanium dioxide and zinc oxide, both of which work by preventing the sun's rays from reaching our skin by reflecting and dispersing them. The chemical sunscreens work by absorbing ultra-violet rays and keep them from penetrating the skin. They are great at blocking about 95% of the UVB rays, but very little UVA. The degree of absorption depends on the type and concentration of chemical sunscreen. Ideally, you'd have a combination of the two in your sunscreen.

To get maximum sunscreen-age, apply it about 15 to 30 minutes before going into the sun so it can penetrate the keratinous layer of your skin. Re-apply it regularly every 2 to 4 hours, and especially if you've been swimming or sweating a lot.

The physical sunscreens are unlikely to cause a reaction on our skin - any reaction you might have is thanks to the other ingredients in the sunscreen - so if you have sensitive skin, stick with zinc oxide and titanium dioxide and be okay with looking a little ghostly (I like this on my face, not so much on my legs!) These sunscreens might feel a little draggy, but it's a small price to pay to avoid sunburns!

If you're out in the sun - meaning, if you ever go outside - don't forget to protect your nose and lips. Your nose gets the most sun exposure, so sunscreen it well. And our lips can be protected with as little as your lipstick on a cloudy day, or with a water resistant sunscreen or lip balm during a sunny day.

Don't forget to get a good pair of UV blocking sunglasses. They'll protect your retinas and they'll make you squint less - and less squinting means fewer wrinkles, so you're looking good as well as feeling good!

How does SPF work? It's all about you! Let's say you burn after 10 minutes in the sun. SPF 15 will get you 150 minutes in the sun. SPF 30 will get you 300 minutes in the sun. But you have to re-apply after about 2 hours with a non-water resistant sunscreen anyway, so what's the point if you take 20 minutes to burn and you have to re-apply it after about 120 minutes? Because SPF 15 will block out about 93% of the UV rays, and SPF 30 will block out about 97%. For very fair skinned people, going from SPF 30 to 50 might get them another 1% coverage. Might not be a big deal for someone who has dark skin, but if you're like my husband (more below), that 1% could mean the difference between a slight reddening of his skin and a burn.

So how do we make our own? We don't.

As you may or may not know, my husband has vitiligo, a condition that leaves him without melanin in big patches in his skin and hair. (This is what they say Michael Jackson had, the condition that was making him white. As Raymond is already quite fair skinned, you don't notice it much.) So we buy sunscreen by the bucketload in the summer to ensure he isn't at risk for burning, which can happen in a few minutes for him. If I could make sunscreen that I could guarantee would work for him, I'd make it. But there are so many factors that go into ensuring a sunscreen works, I don't feel confident that it will prevent him from agonizing pain.

If you're considering making your own sunscreen, there is a lot of chemistry to know. You have to worry not only about the pH of a sunscreen but the emulsification of our lotion when making a sunscreen. As well, how do you know how effective your chosen sunscreen might be? Only by going into the sun and seeing if it works, and anecdotal evidence is not data - it might have been a cloudier than normal day, you might have been under a tree, you might have really sun resistant skin that doesn't burn for 30 minutes or more! If you have a fair skinned friend, she might burn in 10 minutes, and the product that works well for you might mean sunburn for her! 


There are so many scary things out there on the 'net about sunscreen, and I won't give them any validity by putting them into this post. The way I see it? Sunscreens block out the sun's rays. Sun makes me burn. Anything that prevents unnecessary pain today and wrinkling tomorrow works for me. (Click here for a post on pigmented skin through sun exposure and here for a post on photo-aging.)

Yes, I know anecdotes aren't data and this last paragraph is my opinion, but I really haven't found any valid studies showing that sunscreen causes more harm than good. 

If you're worried about sunscreens, then don't use them. Or choose sunscreens containing only certain ingredients, but not others. I hope I've shown you why we shouldn't make our own...

10 comments:

Mich said...

Hi Susan,
Another point to consider is that there are a lot of studies that show that people apply too little sunscreen. The SPF on the label assumes that you are pretty much slathering it on. So don't be skimpy!
Also, there is a good bit of emerging evidence that formulations that include antioxidants offer additional protection from skin damage--if some free radicals are produced, they'll be neutralized before they can cause trouble. (This could also be a good rationale to have lots of antioxidants in apr├Ęs sun sprays or other summertime formulations.)
Keep up the great blogs!

Susan Barclay-Nichols said...

Hi Mich! You're right! I believe I saw something about a shot glass full of sunscreen before going out, and that's about 2 tbsp, right? (I'm on metric, remember!)

Anti-oxidants are a great idea for apres sun sprays - we can use loads of lovely extracts for this, or add some Vitamin E to oil based products! (I forgot to include this in the post, so thanks for the addition!)

When you consider how much you have to use and how much sunscreen can cost, even for a house-brand one, I understand the desire to make them. My husband and I spend a fortune on sunscreen - a week-long camping trip can cost us upwards of $50 - and I wish I could make it myself. (Plus, most of the sunscreens make my rosacea prone skin break out!) But I simply won't take that chance with our health!

p said...

Hi Susan, I've been reading labels of sunscreens in which zinc oxide is the only active ingredient. Because sunscreens are regulated as drugs by the FDA, manufacturers must disclose the percentage of active ingredient - so I've been getting a sense of the numbers, and I can't help but notice that time after time, ~20% zinc oxide gives an SPF 15 to 30, even in really simple formulations (e.g. this sunscreening anhydrous balm: http://www.badgerbalm.com/pc-372-6-spf-30-for-face-body.aspx). I'm super tempted to make a zinc oxide sunscreen for my own use, despite your prudent warnings! I'm dark-skinned and low-risk, and I'd only be hoping for SPF 15, and I'd go with 20% zinc oxide, which is probably overkill. Bad idea? I certainly hear your point about not being able to guarantee effectiveness without testing - but are the pH and emulsification considerations you mentioned as relevant for physical barriers like ZnO? I get the impression that with zinc oxide, it's all about how much zinc oxide you apply to your skin, so a homemade 20% ZnO lotion that you use in the same quantity and frequency as a commercial 20% ZnO lotion should perform similarly, as a very rough guess?

Susan Barclay-Nichols said...

Hi p. This is the problem - you can't just add 20% zinc oxide to something and expect a certain amount of coverage. There are just too many variables that go into making a sunscreen to be able to predict something like "10% zinc oxide provides SPF x".

Here's a PDF on this topic - it's quite interesting, indeed! From this PDF: Nonpolar solvents stabilize the ground state of sunscreens that are nonpolar and thus greater energy (shorter wavelength) is needed to excite these sunscreens. Their curves are seen to shift to the left (shorter wavelength). Typically the SPF decreases.

Water is polar. Oil is non-polar. Zinc oxide is non-polar. If you're making an oil based zinc oxide, you'll need to use more zinc oxide than you think to get the SPF you want because of this shift. The maximum allowable in cosmetics in North America is 25%.

As for pH, in a paper I found (but can't link to as it's on my computer and I don't want post copyrighted material - but I can give you all the information for a search if you want) at pH 4 and 5, 10% zinc oxide had an SPF of 1.1 and 1.5, whereas at pH 6 it was 2.4 and pH 7 it was 4.3. Those are huge differences! And it's really easy to get a little drift to a lower pH when you're formulating. If you're using anhydrous butters and oils, your pH should be around 7 or 8.

The Badger product to which you link is using micronized zinc oxide, which is not the same as regular zinc oxide. 20% regular zinc oxide in an anhydrous product will likely make you appear quite white. (In one of my textbooks it notes that it's almost impossible to make a satisfactory product with 25% zinc oxide alone. It will feel draggy, make your skin look very white, and won't provide as much SPF as a product in which you have titanium dioxide or another sunscreen ingredient.)

After saying all of this, I'm not the formulation police. I'm just offering suggestions and helpful hints for making products. If you really want to make a sunscreen, make a sunscreen. But please don't post the recipe somewhere and encourage others to try it as they might not have the same skin type as you and they could have very different results.

p said...

You've convinced me like no one else has been able to! Thanks so much for the detailed response. I had no idea about the influence of polar/nonpolar solvents. I haven't looked over the pdf yet, but I will shortly. I'd be interested in checking out the copyrighted paper you mention - can you pass along the search terms?

You know how you posted on how you duplicate a product? I would absolutely love an analogous post on how you research ingredients and formulations. You shed so much light on topics that other sites discuss only casually. Do you do your research mostly through books? Or is the web actually a really good resource? I find that when I google many of the ingredients you use, the search results consist of either sites trying to sell a product or anti-chemical screed - neither of which is a source of good, objective information.

Thanks again for your amazing work! It's thanks to you that I'm applying my scientific mind to my hobby. :)

Susan Barclay-Nichols said...

Hi p. After much hassle with Blogger today, here's a post on this topic. I hope it answers some of your questions on how my brain works.

Anonymous said...

Hi Susan,

I was looking up how to make sunscreens and I know you do not recommend this, I never actually wear sunscreens as I hate the feel and they make my dark skin loook grey or purple. Also because I have dark skin I rarely burn (only twice in my life as a kid).

So I've been using the BASF Sunscreen calculator as a guide for research and thought I'd look up some of my existing products foundations, cream etc. and found it interesting although the SPF stated was correct the formulations actually failed is several countries!

I am just wondering if I am one of those poeple who dread wearing sunscreen to the point of actually choosing to burn, even if I formulated my own sunscreen cream however low the SPF may be wouldn't it be better than no sunscreen at all?

Just a thought, thanks for your fantastic blog, I only found it because I bought all your books first from lotioncrafter and realised you had even more excellent information.

-Jessica-

Li Xua said...

I definitely agree that you shouldn't make your own sunscreen, because you have no way of accurately testing it, but what about including pre-made sunscreen as part of a cream? By pre-made I mean ingredients like Croda's SolaVeil line, or other such ingredients made specifically to be added to cosmetic formulations?

Susan Barclay-Nichols said...

Hi Li! Do you have a way of testing the product once you've added the ingredient? Are you completely and utterly sure you aren't using anything that could interact with the sunscreen ingredient and make it lose efficacy? As I have mentioned in many many posts on sunscreens, something that should be a sunscreen ingredient - like titanium dioxide - can be invalidated by using all kinds of incompatible ingredients. Sunscreen is a drug, and we can't make or test drugs at home.

So the short answer is no, I wouldn't if I were you.

Li Xua said...

Makes sense, thanks. I suppose ingredients like that are really meant as a way to make life easier for people formulating commercial products, that have means of testing them.