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Does blotting oily sunscreen reduce SPF?
Emma asks in Gmail…I don’t like the oily skin I get from using sunscreen so I blot off the excess with an oil absorbing sheet. Is this reducing the SPF of the sunscreen?
Yes, blotting some of the sunscreen off your face will reduce the UV protection, to some degree. That happens for two reasons:
First, most UV absorbers are not water soluble so they’re dissolved or dispersed in an oil phase. That means a high percentage of the active ingredient is in the oil that you’re removing. And less of that active ingredient means less sun protection.
Second, good sun protection depends on having a relatively thick, even film of the sunscreen on your skin. In fact, dermatologists specifically talk about sunscreen being wiped away as one of the main reasons to reapply.
Apparently this is well studied because I found a paper titled “Effect of Film Irregularities on Sunscreen Efficacy” in the Journal of Pharmaceutical Science. The researchers tested how well different sunscreen films worked and they found “Nonuniform distribution of sunscreen films on skin…account for large discrepancies between naively predicted efficacy and that observed clinically.” In other words, regardless of how good the sunscreen is, if the film isn’t uniform it won’t work as well.
The bottom line is that blotting off excess oil is one way to disrupt the film so if you want good sun protection, then you shouldn’t do it.
Is it safe to use fabric softener on hair?
Chloe asks…is it safe to use fabric softener on your hair?
I guess this qualifies as another of those DIY beauty hacks that we’ve been talking about lately. I’m not sure WHY you’d want to do this – to save money? To get better conditioning? Regardless of your rational here are 3 reasons this isn’t a good idea:
1. Beware of build up
Fabric softeners have a stronger charge then many hair conditioners. That means they may stick to fabric providing long-lasting softness. This is a good thing when it comes to your close which you wash rather infrequently. However in the case of your hair repeated, frequent use of fabric softer could result in horrific buildup.
2. You want the best for your hair
The ingredients are designed to stick to fabric but they can also stick to your hair after rinsing which is why they work so well. But that’s where the similarity ends. A good conditioner will include some sort of agent to add shine to your hair, for example a silicone. You will not find this in a fabric softener since “shine” is typically not desirable of clothing. The types of quats used in hair conditioners are fine-tuned to deliver the best aesthetic experience possible. The ingredients that are good at softening fabric may leave here feeling heavy and limp with a notable waxy coating. Fabric softeners are also heavily fragranced you may find yourself choking on the scent of Downey or Snuggles compared to your typical salon brand.
3. Skin safety
Of course the biggest concern is one of safety. Cosmetics (despite what other people may tell you otherwise) are formulated and tested to ensure they are safe for prolonged contact with skin. There are multiple regulations which control what may and may not be used in cosmetics.
Not surprisingly the laws that govern fabric softeners are different than the ones that control cosmetics. That’s not to say that fabric softeners are necessarily dangerous but they certainly aren’t intended to be used in direct, prolonged, contact with skin. Let’s look at the ingredients in Downy which is probably the most popular brand.
DEEDMAC: The main ingredient, which provides the conditioning, is diethyl ester dimethyl ammonium chloride (or DEEDMAC). The good news is that studies have found this is NOT a sensitizer on skin. Similar And similar ingredients are used in cosmetics.
Formic acid: which is a skin sensitizer and can produce allergic reactions. Not used in cosmetics.
Benzisothiazolinone: The preservative is a cousin of MI and it’s known to cause allergic reactions in some people. One research paper talked about population allergic to this somewhere between 2% and 23%. This is not used in cosmetics.
Colorant: Liquitint® Sky Blue Dye is a color molecule attached to a couple of polymers. Not approved for cosmetics but needed here to prevent your white towels from staining. Showed that typical water soluble blue dye stains more. This colorant is NOT allowed in cosmetics.
Finally, a word about pH is 4 which is typical for a cationic conditioning product like this. That’s because at a slightly acid pH the conditioner has a positive charge which means it will stick to the damage areas of hair or fabric which have a negative charge.
The bottom line is why would you risk messing up your hair and damaging your skin with a product that’s not designed or tested for personal care use?
What’s a non-irritating alternative for shaving cream?
Peter asks…All regular shaving creams/gels I tested have pH values between 8.5 and 10 and use surfactants like sles or cocamide mea these products leave my skin itchy, red and dry. A dermatologist recommended substituting face wash with a regular emmolient cream and to also shave with it. I tried it with a couple of basic cleansing milks and moisturizers, and my skin is less dry, but it doesn’t really give the same barrier/slip most of the times. So I wonder is it wise to substitute your shaving cream with an emollient moisturizer, and what ingredients have a slippery feeling and give a barrier on skin so that the blade glides easily over your skin?
(Most) shaving creams are true soaps which means they’re formulated with saponified fatty acids (stearic acid usually) and some kind of alkaline agent like triethanolamine (hence the high pH.)
The benefit of this type of formula is that it does a good job of wetting the hair and it provides a lot of lubricious slip. The disadvantage is that it can be irritating to some people. As you pointed out, shaving with an emollient cream is a great idea if you have sensitive skin but, depending on the formula, it may not provide the same level of slip.
Unfortunately, it’s not as easy just telling you which ingredients have a slippery feel because it depends on how those ingredients are formulated into the finished product. For example, many silicones provide a lot of slip but if they’re formulated into a cream with cetyl or stearyl alcohols then the finished product can feel draggy.
This is one of those cases where you’ll have to use trial and error to find an emollient cream that gives you the right level of slip for your personal taste. Having said all that, I do have one off-the-wall suggestion for you. You might try one of those anti-chafing bikini gel products like Monistat product. It’s almost pure silicone so you might like the way it feels. (But it certainly won’t wet the beard hair so maybe it will be harder to cut? I don’t know it’s just a thought.
What’s the deal with ionic hair dryers?
Marta says…How do ionic hair dryers work? I’ve read one website that says they cause H2O molecules to divide into smaller particles that evaporate faster. Another website says the ions themselves offer some benefit to your hair. Could you explain it?
I can’t explain it because it’s not true! We’ve heard this claim for years but I haven’t seen a scrap of evidence showing that blowing ionized hot air at your hair provides any benefit.
Don’t get me wrong – ions do have their place in hair conditioning. Specifically, that’s how certain types of conditioners can stay on your hair after rinsing. One end of the molecule has a positive charge and that sticks to the negatively charged spots on your hair which is where the most damage is. So one end is the “anchor” but the other end of the molecule is a long chain of carbon atoms. This “fatty” part lubricates the hair like a thin coating of oil. If you blow ionized air onto your hair you’re just getting water ions which don’t have the same properties.
Want to learn more about beauty ingredients? Visit Cosmetic Composition.
We’re working on a project with another chemist, Paige DeGarmo, who runs the website www.cosmeticcomposition.com. She does a great job of explaining the science behind beauty products. If you like the Beauty Brains you’ll enjoy her website too. Here are a few of my favorite articles:
How does product order affect skin penetration?
What’s the difference between antiperspirant and deodorant?
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Anonymous59724 says… This is helpful information, presented in an engaging way, definitely accessible for those of use without any more than high school chemistry knowledge. My only complaint is that it’s a little slow-paced, and that occasionally the hosts talk about beauty news articles that aren’t really at all interesting.