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Preservatives in cosmetics – explained!

Many people seem to think that preservatives are the scariest of all cosmetic ingredients. To  give you the scoop on why you need them and what they are, I’m sharing this article which was written as an introduction to cosmetic formulators.

Why you need cosmetic preservatives

There are two primary reasons you need preservatives.

1. To stop microbes from spoiling your products.
2. To stop microbes from causing disease.

The microbes that can infect your formulas primarily include bacteria, mold, and yeast. In small quantities they don’t represent much of a problem but when they multiply, look out. Bacteria like Pseudomonas can cause all kinds of health problems including skin and eye infections, toxic shock, strep throat, and even food poisoning. Yeast like Candida albicans can cause thrush. And many other bacteria can cause your products to smell awful, change color or otherwise break down. (This is what stability testing is for).

The following is a list of common preservatives used in cosmetic and personal care products.

Parabens

Parabens are the most commonly used preservatives. They are derivatives of p-hydroxybenzoic acid and go by names like Methylparaben, Propylparaben, and Butylparaben. They are typically supplied as powders and can sometimes be difficult to incorporate into a system due to the water solubility limitations. They are effective against a broad spectrum of bacteria and fungi. They do have pH limitations and are not effective against all microbes so you usually will need an additional preservative.

Formaldehyde donors

Formaldehyde derivatives are the next most common preservative. These compounds interfere with membrane proteins which kills microbes. They are effective against bacteria, fungi, and mold. Bad press and real safety concerns have led cosmetic chemists to stop using formaldehyde. Instead ingredients that dissociate into formaldehyde when put in a water solution are used. These are compounds like DMDM Hydantoin, Imidazolidinyl Urea, and Gluteraldehyde. They are most often used in surfactant systems.

Phenol derivatives

Phenol derivatives have been used in cosmetics for many years and can be effective against a range of microbes. Unfortunately, they are not as effective as the previous ingredients so their use is limited. The most common examples is Phenoxyethanol.

Quats

Compounds that contain nitrogen and have a positive charge when placed in solution are called quaternary compounds (or quats). Many of them demonstrate an ability to kill microbes. This include ingredients like Benzalkonium Chlroide, Methene aommonium chloride, and Benzethonium chloride. Their cationic nature makes them less compatible with anionic surfactants which limits their application & use.

Alcohol

Ethanol is a great preservative but you need to use it in high levels and it faces significant environmental restrictions. Other compounds like benzyl alcohol, dichlorobenzyl alcohol, and even propylene glycol all have some anti-microbial effect. In lower levels, these compounds are less effective at preserving products.

Isothiazolones

Synthetic compounds like Methylchloro- Isothiazolinone and Methyl-Isothiazolinone are effective at incredibly low levels. They have been shown to work at a wide range of pHs and in many different formulas. There use has been stymied however, by at least one study that suggested it could cause skin sensitization.

Organic Acids & Others

Various other compounds are used as preservatives but all face some limitations not experienced to the same extent as the previous ingredients discussed. Some of the most important include Sodium Benzoate, Chloracetamide, Triclosan, and Iodopropynyl Butylcarbamate. Pyridine derivatives like Sodium pyrithione and zinc pyrithione are used to kill the bacteria that causes dandruff.

Why cosmetic preservatives are vilified

More than any other ingredient, preservatives are most often called out as the worst ingredients you can use in a formula. Even people who know nothing about chemistry have likely heard about the “evil” parabens and formaldehyde.

Preservatives are designed to kill cells. That’s why they are effective. Unfortunately, that’s also why they are potentially hazardous. They don’t easily discriminate between good human cells and bad microbial cells. But ultimately, the risk from using preservatives is significantly lower than that of using unpreserved cosmetics. There are safe levels of “toxic” chemicals. All chemicals can be deadly if you’re exposed to a high enough level. How many people die from water exposure (e.g. drowning)?

Remember, it’s the dose the matters!

To be sure, cosmetic science research is ongoing in the field of preservatives since many things previously deemed safe have been reclassified as hazardous. Suppliers who can come up with even safer preservatives will likely make a lot of money. Hopefully, they’ll do it soon but there do not appear to be any promising materials on the horizon.

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A no brainer way to support the Beauty Brains

Support the Beauty Brains while you shop!

If you like learning about cosmetic products so you can be a smarter shopper and save money, then please support us so we can continue to provide this free service to you.

The easiest way to support us doesn’t cost you a cent. All you have to do is shop online using our Amazon.com link. There’s no extra charge to you but we get a small commission from each sale no matter what you buy. It doesn’t even have to be anything beauty related! ANYTHING you buy really helps us out.

So click now or bookmark this link for later.

Support the Beauty Brains while you shop!

Thanks, Perry and I really appreciate it!

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Baby Foot Pad – Look at the label

Baby Foot Pad is a best selling beauty product on Amazon but is it for babies or adults? Let’s look at the label to figure it out.

Apparently this product is an exfoliant foot peel that designed to give you feet as soft as a baby’s. (So it’s for adults.) Here’s how it works:

First you wash and dry your feet. Then, you place your feet inside plastic booties that are filled with an Alpha Hydroxy Acid mixture and seal them shut with double sided tape.  You leave them on your feet for two hours and when you take them off your feet are buttery soft. (It lends a whole new meaning to the phrase “booty call” doesn’t it? )

I have no idea is this product really works as promised (or if it’s even safe to leave an AHA mixture in contact with your skin for so long!

Baby Foot Pad ingredients

Water, Alcohol, Lactic Acid, Glycolic Acid, Arginine, Butylene Glycol, Peg-60 Hydrogenated Castor Oil, Glucose, O-Cymen-5-Ol, Citric Acid, Malic Acid, Citrus Aurantium Dulcis (Orange) Oil, Citrus Grandis (Grapefruit) Peel Oil, Dipotassium Glycyrrhizate, Cymbopogon Schoenanthus Oil, Nasturtium Officinale Extract, Arctium Lappa Root Extract, Saponaria Officinalis Leaf Extract, Hedera Helix (Ivy) Extract, Salvia Officinalis (Sage) Leaf Extract, Citrus Medica Limonum (Lemon) Fruit Extract, Clematis Vitalba Leaf Extract, Spiraea Ulmaria Flower Extract, Equisetum Arvense Extract, Fucus Vesiculosus Extract, Chamomilla Recutita (Matricaria) Flower Extract, Camellia Sinensis Leaf Extract, Houttuynia Cordata Extract, Phenoxyethanol, Hydroxyethylcellulose, Salicylic Acid

Please support the Beauty Brains by purchasing Baby Foot or ANY other product on Amazon.com. We really appreciate it!

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Where did my favorite pink nail polish go?

Wow, this commercial REALLY creeps me out.

If you watch it without the sound it looks just like the opening to one of those late ’60′s Jack the Ripper proto-slasher flicks. You know the ones…

Defenseless girl hangs out on the dimly lit water front.

The cloaked villain sneaks up on her from behind.

He grabs for her.

She spins around.

He twirls his mustache.

She breaks free and brandishes her pink talons, apparently startling him for a moment.

She smiles coyly and the chase beings anew.

This is supposed to sell nail polish? (Maybe for self defense?)

Believe it or not, there is a beauty science angle to this rant. It can be difficult to recreate these nail colors from the past (especially pink ones) because some red colors have been banned.

Cosmetic colorants are highly regulated

That’s right, I said banned. Many people have the impression that the cosmetics biz is the Wild West where anyone can put anything in any product. Actually that’s not true. Colorants, in particular, are highly regulated. On several occasions, when the research shows there’s is a problem, specific colorants have been prohibited from cosmetics. For some reason those red shades seem particularly pesky. And that means that you may have a favorite red or pink shade that’s no longer available.

For the anal retentive members of our audience, I present to you the list of red colorants banned from cosmetics:

In food, drug and cosmetics

FD&C Red #1 – Removed from list – 81.10(c), 81.30(b)(1)
FD&C Red #2 – Removed from list – 81.10(f), Feb. 13, 1976 – 81.30(j)
FD&C Red #3 – All lakes, all cosmetics, and external drugs removed from list – 81.10(u), Feb. 1, 1990 – 81.30(u). Use of FD&C Red #3, but not its lakes, in food and ingested drugs is allowed.
FD&C Red #4 – Food, ingested drugs, and ingested cosmetics removed from list. Use in externally applied drugs and cosmetics is allowed – 81.10(d), Sep. 23, 1976 – 81.30(c).

In drug and cosmetics only
D&C Red #5 – Sep. 4, 1966 – 81.30(d)
D&C Red #8 – Removed from list Jan. 6, 1987 – 81.10(t), 81.30(s)(1); July 15, 1988 – 81.30(s)(3)
D&C Red #9 – Removed from list Jan. 6, 1987 – 81.10(t), 81.30(s)(1); July 15, 1988 – 81.30(s)(3)
D&C Red #10 – Removed from list Dec. 13, 1977 – 81.10(h), 81.30(k)
D&C Red #11 – Removed from list Dec. 13, 1977 – 81.10(h), 81.30(k)
D&C Red #12 – Removed from list Dec. 13, 1977 – 81.10(h), 81.30(k)
D&C Red #13 – Removed from list Dec. 13, 1977 – 81.10(h), 81.30(k)
D&C Red #14 – Sep. 4, 1966 – 81.30(d)
D&C Red #18 – Sep. 4, 1966 – 81.30(d)
D&C Red #19 – Removed from list Feb. 4, 1983 – 81.10(q)(1)
D&C Red #24 – Sep. 4, 1966 – 81.30(d)
D&C Red #29 – Sep. 4, 1966 – 81.30(d)
D&C Red #35 – Sep. 4, 1966 – 81.30(d)
D&C Red #37 – Removed from list Feb 4, 1983 and June 6, 1986 – 81.10(q)
D&C Red #38 – Sep. 4, 1966 – 81.30(d)

In External drug and cosmetic only
Ext. D&C Red #11 – Sep. 4, 1966 – 81.30(d)
Ext. D&C Red #13 – Sep. 4, 1966 – 81.30(d)
Ext. D&C Red #14 – Sep. 4, 1966 – 81.30(d)
Ext. D&C Red #15 – Sep. 4, 1966 – 81.30(d)
Ext. D&C Red #1 – Sep. 4, 1966 – 81.30(d)
Ext. D&C Red #2 – Sep. 4, 1966 – 81.30(d)
Ext. D&C Red #3 – Sep. 4, 1966 – 81.30(d)
Ext. D&C Red #8 – Jul. 1, 1968 – 81.30(e)
Ext. D&C Red #10 – Sep. 4, 1966 – 81.30(d)

Reference: http://www.fda.gov/forindustry/coloradditives/coloradditiveinventories/ucm106626.htm

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Is more expensive eye shadow really different?

Mamasim asks…Can the processes (methods) as opposed to ingredients, of producing a beauty product be different enough to justify the price differences in the same product type? A makeup artist I like commented in a tutorial that the reason she liked Dior eyeshadows is they have a wonderful texture. She said that when she asked a cosmetic chemist why they said it was because during its production the product was held at the ‘fat combining’ stage for slightly longer than is the norm… (???) I’m interested in knowing if high end companies use more involved methods and this is a reason why their products can be more expensive?

The Beauty Brains respond:

The only unusual “fat combining” process that I’m aware of is the way Perry eats a hamburger and french fries. He eats ALL the fries first THEN he eats the burger.  Isn’t it normal to intersperse bites of the burger with the fries so you can enjoy the flavor of both?  I mean you wouldn’t eat your entire bag of potato chips and THEN eat your ham sandwich, would you? Sheesh! But I digress…

Processing can impact product cost

While we stress the importance of looking at ingredients to understand the quality of a product, there are situations where the ingredients don’t tell the full story. Sometimes HOW the ingredients are put together can be tremendously important to the quality of the finished product. You don’t see this in simple mixtures, like shampoos, but you do see it on more complex products like pressed powders. Case in point: a recent article in Cosmetics & Toiletries revealed that the quality of a powder cosmetic products depends in part on how the powders are pulverized.

The powders used in cosmetics can form agglomerates, or clumps. These clumps prevent the powder from having a smooth application. To avoid these clumps powders are processed to break them into tiny particles. This is commonly done using a piece of equipment called a “Hammer Mill” which basically slams metal hammers against the powder’s surface to break the pieces apart. Most manufacturers used to this type of equipment.

However a more advanced process, known as “Jet Milling,” can break the particles into even smaller sizes and make them more spherical.

Not surprisingly Jet Mills cost more, and not as readily available, as Hammer Mills. That means if a company wants to make a higher quality powder they either have to invest in more expensive equipment or they have to use a contract manufacturer which owns this specialized grinder. In either case the use of jet milling to create a softer feeling product results in an increased price. Therefore it’s unlikely you’ll see this used in bargain products.

So the answer is yes, process can impact cost.

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Does lemon juice lighten hair?

John asks…Do you remember the products that used Lemon Juice to lighten hair? If you do remember do you know how they work? I mean we know how to lighten hair with Peroxide at a pH of 11 or so, how does the Lemon Juice Work?

The Beauty Brains respond:

Of course we remember those products! The most popular of all was probably “Sun In” which is still on the market today. But the interesting thing about “Sun-In Lemon Fresh Hair Lightener” (as it’s formally called) is that the lemon juice is NOT what lightens your hair! Take a look at the ingredient list below and you’ll see hydrogen peroxide which, as you noted in your question, is well known for its bleaching ability. The product may be “lemony” but the peroxide is doing the real work.

Does lemon juice lighten hair?

Will lemon juice do anything by itself? According to one of the hair color chemists that we work with, the answer is “a little bit.” The citric acid found in lemon juice is a very weak oxidizer, so it works like peroxide but much weaker. Typically, people put lemon juice on their hair and then go out in the sun. It takes a lot of lemon juice and heat helps, and the the sun does a lot of the lightening. People want to believe that it is a safer, more natural alternative and, to some degree, it is. It’s really a matter of expectations andhow the results match those.

The Beauty Brains bottom line

If you want a subtle lightening effect and you don’t mind spending time in the sun, lemon juice can work as a natural hair lightening agent. But if you want to lift a lot of color you’ll need something more potent.

Sun-In Lemon Fresh Hair Lightener ingredients

Water, Hydrogen Peroxide, Aloe Vera (Aloe Barbadensis) Leaf Juice, Lemon Juice, Chamomilla Recutita (Matricaria) Flower Extract (Matricaria), Calendula (Calendula Officinalis) Flower Extract, Linum Usitatissimum (Linseed) Seed Extract (linseed), Hydroxyethyl Cetyldimonium Phosphate, Dimethicone, PEG 7 Phosphate, Glycerin, Quaternium 80, Panthenol, Silk Amino Acid, Polysorbate 20, Fragrance, Benzoic Acid, Disodium EDTA

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What’s difference between dry scalp and dandruff? And how do you pick the best kind of dandruff shampoo for you? Also, in our Beauty Science News segment we ponder new research on antioxidants.

Click below to play Episode 33 or click “download” to save the MP3 file to your computer.

Show notes

Beauty Science News

I saw a pair of articles this week that caused me to rethink everything we’ve been told about antioxidants.

  • http://www.futurederm.com/2014/05/19/why-i-never-ever-use-a-self-tanner/
  • http://www.medicalnewstoday.com/articles/276589.php

Question of the week: What’s the difference between dry scalp and dandruff?

Prima asks…A stylist told me the cause of dandruff is sulfur in shampoos and conditioners. Is this true? If it is, why do people also say that weather has an effect on dry scalp?

Let’s just start by explaining the difference between the dandruff and dry scalp.

What is dandruff?

Dandruff is not just a flaky scalp. In fact, your scalp flakes ALL the time but you usually don’t see it because in a healthy scalp the flakes are microscopic. Dandruff occurs when the flakes are large and are accompanied by itching and inflammation.

There are 3 requirements for dandruff to occur:

  1. Oily scalp – Your scalp produces sebum on a regular basis
  2. Yeast – Your scalp must be colonized by a certain strain of yeast (Malassezia globosa). The yeast eat your scalp oil and “poop” out a potentially irritating compound called oleic acid.
  3. A sensitivity to oleic acid – this varies from person to person and explains why some people have no reaction while others develop severe dandruff.

When the scalp is irritated it becomes red and itchy and the body responds by increasing the rate of cell turn over. Now the cells flake off so fast that they clump together and form visible flakes.

Dry scalp is dry skin
Dry scalp, on the other hand, is just dry skin on your head. Your scalp can be dry just like the rest of your skin. It’s just usually less noticeable for a couple of reasons.

First it’s not exposed to frequent washing like your hands. Your scalp may be washed only once a day or every few days for some people. So the scalp has less exposure to drying surfactants.

Second the hair follicles on your scalp produce sebum which tends to keep the scalp moisturized. The skin on the rest of your body doesn’t have the same amount of oil. So there’s less exposure to drying conditions and more protection, but still, dryness can certainly cause your scalp to flake.

The Mayo Clinic has a nice summary of the factors that contribute to dandruff and dry scalp, let’s take a look at those and then we’ll talk about the cures.

Causes of scalp problems

Dry skin – the most common cause of flaking. As we discussed, these flakes are smaller and less oily and you’ll also find them on other parts of the body, such as your legs and arms.

Irritated, oily skin – can lead to seborrheic dermatitis, a condition marked by red, greasy skin covered with flaky white or yellow scales. Seborrheic dermatitis may affect your scalp and other areas rich in oil glands, such as your eyebrows, the sides of your nose and the backs of your ears, your breastbone, your groin area, and sometimes your armpits.

Infrequent shampooing – If you don’t regularly wash your hair, oils and skin cells from your scalp can build up, causing dandruff.

Other skin conditions – people with eczema (a chronic, inflammatory skin condition) and psoriasis (which is marked by a rapid buildup of rough, dry, thick scales) may look like they have dandruff but they don’t.

A yeast-like fungus (malassezia). Malassezia lives on the scalps of most adults, but for some, it irritates the scalp. This can irritate your scalp and cause more skin cells to grow. The extra skin cells die and fall off, making them appear white and flaky in your hair or on your clothes. Why malassezia irritates some scalps isn’t known.

Sensitivity to hair care products – can lead to contact dermatitis can cause a red, itchy, scaly scalp. (This is more likely if you dye your hair or shampoo too often.)

Cures for itchy, flaky scalp

If it’s just dry skin it will respond to moisturizing or to environmental changes. You can also reduce drying agents like shampooing too much.

On the other hand, if it’s dandruff you’re going to need a medicated shampoo. Dandruff treatments are over the counter drugs which means they have to use one of the approved active ingredients. These don’t all work the same way and some have more side effects than others so let’s take a look at these one by one.

Zinc Pyrithione

The most popular anti-dandruff active. Effective against dandruff and seborrheic dermatitis. Works well with almost no side effects. It even reduces irritation of surfactants.

It’s found in Selsun Salon, Head & Shoulders, and others.

Coal Tar

As the name suggests, this active ingredient comes from the coal manufacturing process. It treats dandruff, seborrheic dermatitis and psoriasis by reducing cell turnover. Coal tar is actually a keratoplastic which means it causes the skin to shed dead cells from its top layer and slow down the growth of skin cells. It tends to have a stronger residual odor which some people dislike.

It can be found in products like Denorex and Neutrogena T/Gel.

Salicylic acid

This beta hydroxy acid helps eliminate flakes. It works by causing the skin to swell, soften, and then slough or peel in areas where it is applied. Doesn’t really do much against the fungus. It may require a conditioner to prevent your scalp from becoming overly dry.

Two special warnings associated with Sal Acid shampoos: They should not be used on children or teenagers with the flu or chickenpox. And you should avoid getting salicylic acid shampoo on your genitals.

Can be found in products like “Ionil T Shampoo”.

Selenium sulfide

Another ingredient that both reduces cell turnover and fights malassezia. It’s used in “intensive versions” which indicates it’s even more effective, however, there are some issues:

May also have a little residual sulfur odor.
It may discolor blonde, gray or chemically colored hair.
It may damage jewelry so don’t shower with your bling on.

Found in Selsun Blue and the Intensive version of H&S.

Ketoconazole

Formerly available only by prescription, this antifungal drug fights the cause of dandruff. However it has several potential side effects: it may cause abnormal hair texture, loss of curl from a permanent wave, hair discoloration, and oiliness or dryness of the hair and scalp.

Found in Nizoral shampoo.

Piroctone olamine aka Octopirox

An active not currently approved in the US. Because of its solubility in water and alcohol it can be used to make clear products. (Most dandruff shampoos are creamy.) However it’s unstable in light so if you make a clear product and then show it off in a clear bottle the light will degrade the active ingredient and it won’t work. May also be inactivated by some perfume oils.

Not found in the U.S.

Prescription drugs

If none of these over the counter dandruff shampoos work for you, ask your doctor for prescription dandruff fighters like Loprox or steroid lotions.

Dandruff myths

We mentioned at the beginning that there’s a lot of misinformation around dandruff so let’s finish up today’s show by busting a few myths, starting with the ones Prima mentioned.

Sulfur in hair care products cause dandruff
Myth: Actually sulfur is part of anti-dandruff ingredients! It helps get rid of it, not cause it!

Weather causes dandruff
Myth: Low humidity can trigger dry skin which leads to flaking but weather alone does NOT cause dandruff.

You can catch dandruff from someone
Myth: Dandruff isn’t an infection, which means it can’t be caught from contact with people with dandruff. You have to have an individual sensitivity or predisposition to it.

Dandruff is caused by poor hygiene
Myth: While washing your hair helps, this is a common misconception. It’s actually our intrinsic susceptibility to irritation,  sebum (a substance found on our scalps) and a micro-organism that lives on our scalp that really causes dandruff. Of course, while dandruff isn’t simply a result of poor hygiene, washing your hair regularly with dandruff can certainly make a big difference.

Styling products cause dandruff
Myth: No, but some styling products leave a flakey residue that looks like dandruff. (From the resins that hold your hair in place.)

Dandruff is caused by dry scalp
Myth: This is a little redundant at this point but actually dandruff has nothing to do with dryness – rather it’s caused by too much oil.

If a shampoo says it removes flakes then it’s a dandruff shampoo
Myth: Some clever marketers imply their products are dandruff shampoos by talking about removing visible flakes (which ANY shampoo will do.) Burts Bees “Feeling Flakey” is an example.

Copper brushes cure dandruff
Myth: Copper does have anti fungal properties and although some people swear by this, we can’t find any evidence that it’s true.

The Beauty Brains bottom line

It’s important to understand whether you truly have dandruff or just dry scalp. Then you can decide how to best take care of your scalp. A ZPT-based shampoo is generally accepted as the best but there are several different active ingredients you can choose from if your scalp is particularly flakey. And now you know that sulfur in shampoos and the weather do NOT cause dandruff!

LIL buy it now button

Buy your copy of It’s OK to Have Lead in Your Lipstick to learn more about:

  • Clever lies that the beauty companies tell you.
  • The straight scoop of which beauty myths are true and which are just urban legends.
  • Which ingredients are really scary and which ones are just scaremongering by the media to incite an irrational fear of chemicals.
  • How to tell the difference between the products that are really green and the ones that are just trying to get more of your hard earned money by labeling them “natural” or “organic.

Click here for all the The Beauty Brains podcasts.

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What does viscosity mean?

This article originally appeared on my other website (the one that Randy always accuses me of cheating on him with.) Even though it’s intended for formulation chemists, I thought the Beauty Brains audience might appreciate an explanation of what is often referred to as “thickness.”

Cosmetic viscosity

You’ll be hard pressed to find a cosmetic formulation that doesn’t involve some understanding of rheology. Single point measurements are often used on specifications for release of products and raw materials in manufacturing, toothpastes need to flow when squeezed from the tube but not drip off a toothbrush, and body washes that contain beads need yield value to prevent them from settling out.

Cosmetic Viscosity Science

Viscosity is a measure of a fluid’s internal friction (resistance to flow) when one layer of fluid is forced to move in over another layer. A fluid may be made up of molecules that vary in size, shape, and cohesiveness or a single type of molecule. As these molecules are forced to move or flow past each other, the molecular properties will determine just how much force is required to move them past each other. The force required to cause movement is referred to as shear. Just a few examples of shear forces in cosmetics: spraying hair products, pumping products into packaging during manufacture, spreading of lotion on the skin, and pouring shampoo from a bottle.

Viscosity is typically measured with a device like a Brookfield Viscometer. This instrument has a rotating spindle attached to a force measuring meter. When the spindle is submerged in the sample, it gives a viscosity reading based on the force required to maintain a specific rotating speed.

Types of Flow Behavior

For Newtonian fluids viscosity is constant at varying shear rates. Water and thin oils are examples of Newtonian liquids. This type of fluid is easiest to measure, but fairly uncommon, as you will encounter far more complex fluid behaviors in cosmetics.

There are many types of non-Newtonian behavior, and the term basically defines any fluid that exhibits changes in viscosity with variations in shear rate.

Shear Thinning – Most cosmetic products like emulsions and suspension are shear thinning, meaning that viscosity decreases with increasing shear rate. This behavior is also referred to as pseudoplastic and is the result of structural breakdown within the fluid.

Dilatant flow — This is just the opposite. Viscosity increases with increasing shear. This type of flow behavior is pretty rare but examples include quicksand and slurries of cornstarch.

Thixotrophic materials — These products thin with constant shear rate but recover their structure and thus increase in viscosity over time once the shear force is removed. Occasionally sheer thinning behavior is misinterpreted as thixotropy, so it is important to remember the distinction for thixotropy is that thinning occurs at a constant shear rate over time as opposed to thinning at an increasing shear rate in sheer thinning behavior. Viscosity can also increase with shear forces like shaking or mixing and then lower to the original value in what’s described as rheopectic behavior, but this type of behavior is also rare. Both thixoptrophy and rheopexy can occur in with other types of flow behavior and the initial viscosity may not be fully recovered.

Yield Point

Another important rheological value is the yield point. Some fluids behave like solids at rest but flow like liquid and decrease in viscosity once the yield value or yield point is exceeded. Fluids with high yield points can easily suspend particles like mica or pigments in cosmetic preparations.

By taking into consideration these types of fluid behavior the cosmetic formulator can select for the rheological properties of cosmetic formulations through choice of ingredients and processing conditions, as well as learning to trouble shoot product failures.

And by the way, ketchup is not thixotropic. See if you can reason why.

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Beauty Science News – June 1

It’s a new month and here are 5 new beauty science news stories to kick it off…

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Badger Baby Sunscreen – Look at the label

Remember, you can support the Beauty Brains by purchasing any of the products we review or ANY product using our Amazon link.

Badger Baby Sunscreen Cream

Badger Baby Sunscreen is a beauty best seller on Amazon.  Let’s look at the label.

The label provides clear directions on product use, except for the dosing part. I don’t think that “2mg/2cm2 of skin” gives most people a reference point for how much to use. It’s better to say something like “use a shot glass full for your body” or something like that.

Knead tube before each use. For full protection, apply liberally (2mg/cm2 of skin) to all exposed skin 15 minutes before sun exposure, then rub in to reduce whitening effect. For children under 6 months of age: ask a doctor. Reapply: After 40 minutes of swimming or sweating. Immediately after towel drying. At least every 2 hours.

Ingredients

Active Sunscreen Ingredient: Non-Nano, Uncoated Zinc Oxide 18.75%

Other Sunscreen Ingredients: Helianthus Annuus (Organic Sunflower) Oil,  Cera Alba (Organic Beeswax), CO2 Extracts of  Hippophae Rhamnoides (Organic Seabuckthorn), and  Calenduls Officinalis (Organic Calendula), Anthemis Nobilis (Organic Chamomile) Essential Oil, and Tocopherol (Sunflower Vitamin E).

This doesn’t appear to be a complete ingredient list since water, emulsifiers and preservatives are not listed.  So I went to their website looking for additional information. I found that the preservative is  “Natural Leuconostoc Ferment Filtrate (from Radish Root).” We’ve written before about the issues using natural preservatives instead of proven protectants like parabens. In this case, the concern is justified since in September 2013, Badger voluntarily recalled its SPF30 Baby and Kids Sunscreen Lotions due to bacterial contamination. They are in the process of reformulating their product line, hopefully with a more robust preservative system.

 

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