Shelf Life of Cosmetics

8/11/2019 Shelf Life of Cosmetics

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Kosmetik Konzept KOKO GmbH & Co.KG • D-42799 Leichlingen • Moltkestr. 25 • www.dermaviduals.com • page 1 of 3

Shelf life of cosmetics - what makes cosmeticproducts unstable?

published in Kosmetische Praxis 2008 (1), 12-14

Cosmetic products have a life of their own, all the more the higher the content ofphysiologically usable skin care substances. Also external influences have to be con-sidered specifically when the products are bottled in jars. In the end, a mix of differentinfluences determines the shelf life of the products. The following article will providean overview on this issue.

any of the substances used in cos-metics have a quite extended shelf lifeif we look at their pure state. In other

words, this means that substances like glyc-erol, urea and amino acids which support theNMF (natural moisturizing factor) of the skinhave a nearly unlimited shelf life. The sameapplies to lipids and oils like neutral oil (satu-rated triglycerides gained from palm oil), paraf-fin oil and synthetic esters.

Water - a delicate substance

Cosmetics are produced by mixing activeagents, lipids and oils with the help of emulsi-fiers and water. This is how creams, lotions

and cleansing products are produced. Withinthese mixtures interactions between the differ-ent substances will occur. Components maychemically react with each other, physicallyseparate or degrade microbiologically due totheir water content. And, if on top of it vitaminsor lipid substances with essential fatty acidsare used which already have a short shelf lifein their pure form, matters still become morecomplicated. Additives like preservatives, anti-oxidants or substances to control the consis-tency may extend the shelf life however onlyfor a short period of time.

Indifferent substances

It is a matter of fact that cosmetic trade as wellas consumers rather prefer the longest possi-ble shelf life. However a long shelf life can onlybe achieved with quite indifferent and unphysi-ological ingredients as for example mineral oilproducts like paraffin oil. During their storageall natural oils including the above mentionedneutral oil are submitted to change in chemical,microbiological and sensory respect. Compro-mises are therefore necessary regarding thedurability of physiological skin care products.

Best before...

Unfortunately legislation was not consequent

enough in regulating the shelf life labelling. Aminimum durability of up to 30 months has tobe marked on the product. A durability of morethan 30 months has to be shown with an open jar symbol and the number of months theproduct still is fresh from the date of openingas for example 6 M for 6 months (see fig.).

Fig.: open jar symbol

The open jar symbol shows the freshness date afteropening (in months), e.g. 3 M for 3 months.

It is self-evident however that products with

sensitive vitamins and extracts (shelf life up to30 months) should only be used over a shortperiod of one, two or three months. In otherwords though, the open jar labelling woulddefinitely make more sense in this specificcase than it does for insensitive and highlypreserved products. A number of responsiblecosmetic manufacturers however now alsovoluntarily labels their products with a shelf lifeof less than 30 months with the open jar sym-bol in particular as the consumers are notreally familiar with the complicated labellingprocedures. It should also be mentioned that

there is no regulation regarding the date statedin combination with the open jar symbol.In addition to that the Cosmetic Degree makesno distinction between jars and dispensers.

M



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Dispensers cannot be contaminated from out-side as there is no direct contact between fin-gers and the product in the dispenser.

Cloudiness, discoloration & Co

Not all the visible changes in a product will alsosignify the knockout regarding its further use.Pure oils for example may appear cloudy orshow precipitations when stored in the re-frigerator. Top-quality avocado oil e.g. precipi-tates phytosterols when stored in low tem-peratures (refrigerator). What may lead to irri-tations in optical respect actually is a qualityfeature here.Discolorations though have to be seen from amore critical standpoint as they may resultfrom oxidation processes. Discolorations inaqueous, yellowish marigold-containing prod-

ucts (calendula officinalis) belong to this spe-cific type.Sediments may form in pigment-containingcreams with low viscosity. But also this defectonly concerns the appearance of the productand can be remedied by shaking before use.If an emulsion disperses into oily and waterycomponents the functionality of the product isaffected. This however should not happenbefore the best of date.Changes in the viscosity of a product seemquite normal to a certain extent especially ifnatural products are used with different agent

content depending on their specific prove-nance and their harvesting time. If substanceslike sodium carbomer or related substancesare used to control the consistency, already aslight decline of the pH level (the acidity grade)may lower the viscosity of the products duringtheir storage.

Chemical reactions

A decline of the pH-level may be caused bythe release of organic acids from triglycerides -the slow reaction with water results in a hy-drolysis of esters. The process as such is notspecifically critical, subject to the condition thatthe released acids will not develop unpleasantodours. Neutral oil for example may develop abuck-like smell, which of course should nothappen before the expiry date.An increased pH-value may occur if alkalinemetal oxides like zinc oxide bind acids andhereby form metallic soaps. Zinc oxide mayalso cause saponification. This is the reasonwhy it mostly is combined with indifferent par-affin oils. The pH-value may also increase in

the presence of urea; with water available itslowly is transformed into ammonium carbami-nate.

The reverse process of the saponification isthe ester formation from acids and alcoholswith formation of water. This process is char-acterized by a lightly fruity smell especially ifacetic acid (from acetates) and ethanol arepresent and ethyl acetate is formed. Said

process however will not influence the shelf lifeof the product. In case of perfumed productsthese processes are blanketed and there areno sensory changes noticeable.Quite bad odours develop however during theoxidation and splitting of unsaturated fattyacids. The human nose already detects therancid odour of the developing long-chainedaldehydes in the ppb (parts per billion) range.Oxidations by atmospheric oxygen usuallyare a limiting factor for the shelf life as theformed oxygen compounds as e.g. from eth-oxilized alcohols (emulsifiers) may cause irrita-

tions, or the unsaturated fatty acids may bestimulated to polymerize by radical formationwhich means that they are no longer availablefor the skin. This is the reason why antioxi-dants like vitamin C and E are indispensable informulations that contain natural substances.Vitamin A and its derivatives also are sensitiveto oxygen, e.g. their efficiency is graduallydecreasing during the life cycle of the product.As there are no immediate side effects to re-alize it is up to the cosmetics manufacturers todecide at which state the product still is effec-tive.

Microbiologically stable?

With respect to health the microbiological sta-bility has first priority for the shelf life specifica-tion. Hence, new products are closely scruti-nized and microbiologically tested withproblematic germs already during the de-velopment phase. And by the way, this appliesfor preserved as well as non-preserved prod-ucts.The assumption that non-preserved productswill earlier contaminate than preserved onesexclusively applies for ampoules which canonly be stored for a few days in the refrigeratorafter opening.Non-preserved means, that none of the pre-servatives listed in the Appendix of the Cos-metic Decree (potentially sensitizing sub-stances) are contained in the product. Alcoholor substances with alcoholic hydroxyl groups(glycols, sorbitol etc.) as well as water phaseswith high osmotic pressure (hypertonic) alsostabilize the products however without a sensi-tizing potential worth mentioning.

Long term effects may become a risk whenpreservatives from container materials (plastic,seals) are absorbed or e.g. the alcohol evapo-rates after opening of the products, and as a



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result the alcohol content gradually falls shortof the microbiologically effective concentration.The manufacturer is required to accurately testthis and subsequently adjust the shelf life ofthe products.Based on the results of the microbiological

tests it is decided whether the products areappropriate for bottling in dispensers or alsoin jars. Oleogels i.e. water free products arevery stable in microbiological respect as germscannot survive in this environment.

Sensory changes

Concluding, the sensory changes should alsobe mentioned as e.g. the fact that volatile per-fumes may evaporate, be absorbed by thecontainer materials or that perfume substancesmay react with each other or with atmospheric

oxygen or water. The manufacturer has todecide, what still is acceptable for consumersduring the product's lifespan.

Summing it up: physiological or extendedshelf life?

Products with a quite extended shelf life usu-ally contain substances which are highly stablein chemical and microbiological respect. Themore physiological the products are the moresensitive substances are contained and hence,the shorter the shelf life. This can also be ex-

perienced with groceries: food which is rich invitamins cannot be found in cans with a longshelf life.

Dr. Hans Lautenschläger

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Shelf Life of Cosmetics