Comedogenic Effects of Cosmetic Raw Materials

by Florence Barrett-Hill Skin Treatment Therapist CIDESCO and ITEC Diplomasby Florence Barrett-Hill Skin Treatment Therapist CIDESCO and ITEC Diplomas

Author: Florence Barrett-HillAuthor: Florence Barrett-HillI am writing this article to clarify some of the misconceptions re the word comedogenic. Since the word comedogenic has become a bit of a buzzword in our industry, many therapists prick their ears up when the word is mentioned. Its seems like its a dirty word in the beauty industry, and everyone likes to hear of something detrimental about someone elses skincare line. Comedogenic does not mean the product is no good, nor does it mean that its unusable.

What it does mean, is that the product is unsuitable for an oily, active or acneic skin. The therapist has a professional responsibility to ensure her skin analysis is correct. If this is done properly and she has an understanding of the importance in linking cosmetic formulations to skin conditions. No mistakes will be made.

What the therapist can not have any control over is what the client buys in the domestic retail market. Foundations, blushers, concealers, lipsticks and lip pencils are very often comedogenic. These types of cosmetics are applied on a daily basis and left on the skin for up to 8 hours at a time. If they contain comedogenic substances and they are applied to an active, oily or acneic skin, comedones will often be the result.

The modern day skin treatment therapist should be aware of all cosmetic formulation side effects, it there are any. The realization that certain products, including cosmetics where responsible for causing acne-like effects became apparent during and after the Second World War, when it was found that people working with polychlorinated hydrocarbons developed comedones similar to those found in acne.

In 1956, Scientists developed a testing procedure using rabbits ears to study the effects of these chlorinated compounds. Further testing in 1968 showed that human sebum applied to the external ear of the rabbit resulted in comedones. This discovery led to the implication in 1972 that the rabbit ear was a useful model for testing cosmetics and raw materials for comedogenic activity. This induced acne-like condition became known as "acne cosmetica", and became the benchmark of significant exploration of this test procedure by several of the larger cosmetic companies at the time.
As research continued, studies proved that persistent eruption of acne-like comedones occurred in over 30% of adult women. This was attributed to certain base materials present in the cosmetics, such as isopropyl myristate. Half of the facial cosmetic products tested at the time, were found to be at least mildly comedogenic in the "rabbit ear test".

The "rabbit ear test" produced a measurable scale of comedogenicity, ranging from 1 to 5. In this manual the same five point grading scale will be used to demonstrate the comedogenic effects of various cosmetic raw ingredients commonly used today. 

The Scale
Grades 1 to 2 are considered non-to mildly comedogenic and grades 3 to 5 are considered significantly comedogenic. The ingredient score is displayed as a score out of 3 or 4. Example: 1/3, 2/3, 3/3, 3/4etc. When the score shown is 3/3, or 4/4, this means that the test ingredient produced a maximum score against the reference maximum.
Variations on concentrations affected the results of the tests, but certain strongly comedogenic materials remained severely irritating even when diluted to 5 and 10 %.

What it means
Products with high concentrations of any of the substances with a rating of 1/3 or more should be avoided with acne prone skins. Concentrations of substances with a rating of 2/3 - 3/4 should be avoided on any other than severely lipid dry skins, as they are severely comedogenic.
It is not uncommon for the composition of products to change although the brand name remains the same. Therapists must be ever vigilant.
The substances in the following tables are commonly found in cosmetic products manufactured worldwide. They have been grouped together in chemical types for ease of comparison. It is not uncommon for several of these substances to be found in the one product. 

The Comedogenicity test results used in this article were sourced from a scientific paper written by Monroe Lanzet, a cosmetic chemist from Lanzet Associates of California, USA. They are the correlation of data from several independent cosmetic manufacturers in the US.

Table 1: Isopropyl Esters
Isopropyl esters are widely used in cosmetics to produce a light, non-greasy, emollient that feels good on the skin. They are manufactured from various compounds including edible fats, oils and lanolin derivatives.
They are normally quite comedogenic when undiluted, but when used in concentrations of 5%, are safely used as part of an otherwise non-comedogenic oil phase with no comedogenic effects. 

Chemical Rating/score
Isopropyl linoleate 3/3
Isopropyl myristate 3/3
Isopropyl palmitate 2/3
Isopropyl lanolate 3/3
Isopropyl isostearate 3/3
Di isopropyl adipate 0/3

Non-comedogenic ingredients
None of the silicones commonly used as a base in ointments and skin protectants tested as comedogenic. (see table 2)

Table 2: Silicones

Chemical Rating/score
Dimethicone 0/4
Dimethicone copolyol 0/4
Silicone wax, 10% in dimethicone 0/4 
Stearoxy dimethicone, 10% in dimethicone  0/4 
Cyclomethicone 0/4

Table 3: Surfactants & pigments
The emulsifier and surfactant sodium lauryl sulphate, although non-comedogenic, shows conflicting results possibly from it's high degree of irritancy. It appears comedogenic, but it's true irritation effect manifests as excessive keratosis, hypokeratosis or ulceration.
It may also cause skin drying because of it's degreasing ability, and is found most commonly in emollient creams, cream depilatories, shampoos and hand lotions.
The common water-soluble cosmetic pigments shown on table 3 also tested non-comedogenic.

Chemical Rating/score
Sodium lauryl sulphate, 5% in water 3/4
Sodium lauryl sulphate 1% in water 2/3
Iron oxides, 25% in propylene glycol 0/4
Titanium dioxide, 25% in propylene glycol 0/4

Table 4: Hydrocarbons
Because of the properties of hydrocarbons, they are used in the cosmetic industry quite extensively as lubricants in lipsticks and in creams, as it helps make them smoother and shiny. The oily film of hydrocarbon based ingredient helps to prevent evaporation of moisture, in addition to helping soften and smooth the skin in the same way as any other emollients. They are often used in preference to other ingredients because they are less expensive.

Chemical Rating /score
Petroleum Distillate 1/3
Polyethylene, 50% in mineral oil 0/3
Polybutene 0/3
Petrolatum 1/3
Mineral Oil, light 1/3
Isoparaffin c8-9 0/3
Isoparaffin C9-11 1-2/3
Isoparaffin C11-13 0/3
Isoparaffin C13-16 2/3
Squalene 1/3

The level of refinement of the base ingredient would dictate the level of contamination, and the quantity used in the cosmetic would be an aggravating factor in the comedogenicity of the final product.
Mineral oil and petrolatum are shown to be mildly comedogenic, as are most high refinement petroleum products. However, some others are more comedogenic, this may be due to contamination. Both mineral oil and petrolatum are shown comedogenic because of their occlusive properties when used on incorrect skin conditions. 

Table 5: Oleic/ Oleyl & alcohol
Both oleic acids and oleyl alcohol are extremely comedogenic. They are used in preference to full weight vegetable oils because of their superior skin penetrating properties.
They are derived from either animal, fish or vegetable oil sources and are used in cold creams, nail polish, toilet soaps and liquid make-ups. 

Chemical Rating /score
Oleic acid 3/3
Oleyl alcohol, 50% in propylene glycol 3/3
Oleyl alcohol, 10% in propylene glycol 2-3/3
Decyl oleate 2/3
Isodecyl oleate 1/3
Oleth-2, 2% in propylene glycol 1/4

The data above also shows that dilution of oleyl alcohol within a non-comedogenic carrier substance such as propylene glycol will not significantly reduce the comedogenic effect.
The severity of comedogenic reactions from oleic acid may be moderated in some formulations by glycerin, a non-comedogenic substance commonly used as a solvent, humectant or emollient.
As shown below, certain saturated acids and alcohol used as cosmetic lubricants and emollients have comedogenic potential.

Table 6: Sorbitan / Methyl Glucose
Sorbitans are generally found as emulsifiers and stabilisers in creams and lotions, and are insoluble in water. Sorbitan oleate is less comedogenic than oleic acid and sorbitan sesquioleate is non-comedogenic. Oleic acids, when combined with sorbitan, reduce potential comedogenic effects. Similarly, Methyl glucose sesquistearate when combined with sorbitan, decyl or isodecyl, reduces comedogenic effects, but when used in combination with isopropyl alcohol or propylene glycol, may enhance comedogenicity.

Chemical Rating /score
Sorbitan laurate 0/3
Sorbitan oleate 2/3
Sorbitan sesquioleate 0/3
Polysorbate-60 0/3
Polysorbate-80 0/3
Methylgluceth sesquistearate 0/3

Methylgluco sesesquistearate
10% in propylene glycol

1/3

Table 7: Effects of physical dilution
The real severity of comedogenic response is best demonstrated by dilution. In table 7 octyl palmitate, a typical ingredient in sunscreens, scores 3/3, as does oleyl alcohol (see table 5). The comedogenecy of octyl palmitate is reduced to 1/3 at 50% dilution, and 0/3 at 5%. Oleyl alcohol when similarly diluted remains 3/3 at 50% and is still 2/3 at 10%.
Conclusions from this comparison indicate that oleyl alcohol is a far more comedogenic substance than octyl palmitate. People with acne prone skin conditions should therefore avoid products containing oleyl alcohol. They may however, tolerate small to moderate concentrations of octyl palmitate without adverse effects. The emollient Isopropyl myristate, which scores 3/3 (see table 1) shows similar dilution characteristics as oleyl alcohol. 

Chemical Rating /score
Octyl Palmitate, 100%  1/3
Octyl palmitate, 50%   1/3
Octyl palmitate, 5%  0/3

Table 8: Lactates
Myristyl lactate is a relatively severe comedogenic ingredient used commonly in moisturisers and sunscreens. Its dilution to 50% in a propylene glycol base will not reduce its comedogenic score. However, when combined with cetyl alcohol, the severity of any reaction is significantly reduced.

Chemical Rating /score
Myristyl lactate 100% 2-3/3, 3/4
Myristyl lactate, 50% in propylene glycol 2-3/3
Myristyl lactate, 50% in cetyl alcohol 0-1/4 

Table 9: Effects of Un-saturation on Comedogenicity
A relatively large number of vegetable oils used as emollients in moisturisers, soaps, cleansers and sunscreens, were found to show comedogenic effects ranging from 0/3 to 3/3. This is an alarming and embarrassing discovery for the Beauty Therapy industry, as many of these vegetable oils have been used as carriers in aromatherapy and massage oils for many years. With this in mind, it is now obvious why beauty therapy students often complain that their skins were just fine until they started their training.
Saturated triglycerides are generally far less comedogenic than unsaturated oils (avocado oil is an exception), and sunflower seed oil is far less comedogenic that sweet almond or grape seed oil.

Chemical Rating /score
Capric/caprylic triglyceride 2/4
Hydrogenated vegetable oil 1/3
Coconut oil 2/3
Hydrogenated lard glyceride 0/3
Avocado oil 0/3
Castor oil 0/3
Peanut oil 1/3
Hybrid safflower oil 1-2/3
Peach kernel oil 2-3/3
Sweet almond oil 3/3
Grape seed oil 2-3/3
Sunflower seed oil 1/3

Table 10: Glycols and Glycol Esters

Glycols are water-soluble substances commonly used in cosmetics as humectants. Table 10 shows the moderating effect of the noncomedogenic substances glycerin and propylene glycol. As a good rule of thumb, water-soluble materials are generally minimally comedogenic. Glycerol and glycol stearates are minimally comedogenic, but are not moderated by dilution in propylene glycol. Glyceryl oleate, by virtue of it's severely comedogenic cousin, decaglyceryl decaoleate, is probably at least moderately comedogenic. No data was available on glyceryl oleate itself, but the conclusion that it is comedogenic is drawn from the fats and oils studied in table 9.

Propylene glycol tends to prevent comedogenicity by modifying the molecular structure and chemically diluting any comedogenic elements.

Chemical Rating / score
Glycerin 0/3
Glyceryl stearate 0-1/3
Glyceryl stearate, 30% in propylene glycol 0-1/3
Glyceryl stearate, 10% in propylene glycol 0-1/3
Decaglyceryl decaoleate 2-3/3
Glyceryl triacetyl ricinoleate 0/3
Propylene glycol 0/3
Propylene glycol stearate 1/3
Propylene glycol decaprylate/dicaprate 0/3
Glycol stearate, 10% in propylene glycol 0-1/3

Table 11: Lanolin and Lanolin Derivatives

Lanolin is a mildly comedogenic substance found in a variety of cosmetic products. Considered a wax rather than fat, an essential component of lanolin is cholesterol. Lanolin oil is a fluid fraction of lanolin and, as expected, has the same minimal score as lanolin.
Lanolin alcohols, of which cholesterol is the best known, is also minimally comedogenic and is noncomedogenic when, diluted to 10% or less.
The offending comedogenic element of lanolin is lanolic acid. Dilution of lanolic acid to 10% in corn oil does not lessen its severity. Derivatives of lanolic acid, such as isopropyl lanolate, and hydrogenated lanolin, also contain lanolin acids, and are similarly comedogenic.

Chemical Rating /score
Lanolin 0-1/3
Lanolin Oil 0-1/3
Lanolin alcohol, 100% 1/3
Lanolin alcohol, 10 % in mineral oil 1/3
Cholesterol 0/3
Lanolic acid 3/3
Lanolic acid, 10% in corn oil 3/3
Isopropyl lanolate 2-3/3
Hydrogenated lanolin 2/3
Acetylated lanolin alcohol 2-3/3
Laneth-5 1/3
Laneth-20 0/3
Laneth-10 acetate 2/4-1/3

Table 12/13/14: Fatty Alcohols and Fatty Acids

This group of substances is derived from a multitude of sources including fish, animals and plants. Myristyl, cetyl and stearyl alcohols are noncomedogenic, but unsaturated alcohol such as oleyl, isostearyl and octyl dodecanol are moderately to severely comedogenic. Hexadecyl alcohol is also known to be severely comedogenic. The acids in this group are more comedogenic than the equivalent alcohols. Stearyl alcohol is minimally comedogenic while stearic acid scored higher. Isostearic acid must be considered severely comedogenic because of the high score even at 10% dilution in propylene glycol.

Table 12: Fatty Alcohols

Chemical Rating / score
Lauryl alcohol, 50% in mineral oil 1/3
Myristyl alcohol, 50% in mineral oil 0/3
Cetyl alcohol 0/3
Stearyl alcohol 0/3
Oleyl alcohol, 50% in propylene glycol 3/3
Oleyl alcohol, 10% in propylene glycol 2-3/3
Isostearyl alcohol 3/3
Isostearyl alcohol, 10% in mineral oil 2/3
Octyl dodecanol 2/3

 
Table 13: Fatty Acids

Chemical Rating /score
Stearic acid  1/3
Stearic acid, 50% in mineral oil 1/3
Oleic acid  3/3
Isostearic acid, 50% in propylene glycol 3/3
Isostearic acid, 10% in propylene glycol 2-3/3


Table 14: Alcohols, Glycols and Polyglycols

Chemical

Rating /score

Glycerin 0/3
PEG 200 0/3
PEG 300 0/3
PEG 8 0/3
Butylene glycol 0-1/3
Propylene glycol 0/3
Hexylene glycol 2/3
Benzyl alcohol 0/3
Ethyl hexane diol 0/3
Polypropylene glycol 15-200 0/3

Table 15: Assorted Esters and Ethers
Both esters and ethers are derived from alcohols and used in the manufacture of emollients. Used to improve the feel or humectant qualities of cosmetics, they have been found to be mildly to severely comedogenic. Many are commonly used as moisture carrying vehicles instead of water, and although giving better permeation through the skin, they are often linked to sensitivity reactions.
Those listed below are commonly used in the industry. As shown, even when diluted with propylene glycol they show very small changes in the comedogenicity.
Butyl stearate and oleyl alcohol are in the extra severe class, promoting comedogenicity on minimally comedogenic substances even when diluted down to concentrations of 5%.
Cosmetics containing these materials should be avoided by people with oily or acne prone skins.

Chemical Rating /score
Triethyl citrate, water soluble 0/3
PPG 2 myristyl propionate 0/3
Myristyl myristate 2/3
Myristyl propionate 2/3
Myreth 3 myristate, 50% in propylene glycol 3/3
Myreth 3 myristate, 10% in propylene glycol 2-3/3
PPG 15 stearyl ether 2/2
Isocetyl stearate 0/3
C12-C15 alcohols benzoate 3/3
Butyl stearate, 100% 2/3
Butyl stearate, 5% in mineral oil 1/3
Isostearyl neopentanoate 0/3
Isodecyl isononanate 15-200 0/3

This article was originally published in 2001.  For more information on the subject of cosmetic chemistry, click here.


About the Author:

Florence Barrett-Hill is an internationally acclaimed dermal science educator, practitioner, researcher and author with a vast experience covering all aspects of professional aesthetic therapy and paramedical skin care. Florence holds over a dozen diplomas and international qualifications covering every aspect of modern skin treatment therapy, and is well respected by her industry peers for her 30+ years of knowledge she loves to share.
Florence is the programme director of Pastiche Resources, an Internationally recognised postgraduate beauty industry education provider.

 


 

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