What is shelf life?

Shelf life of any product is the time within which it should be consumed. Within that time, if the product is properly handled, it is not expected to significantly change from the condition in which it left its manufacturer; it should conform to the information on its original label, including its description, indications, and methods of use and storage.

Proper handling is essential to having a product achieve its expected shelf life: if it is meant to be protected from heat or light but that protection is not provided, the product will degrade more quickly and may become unusable or unsafe within its predicted shelf life.

When does shelf life begin?

There are several possible starting points for reckoning a product's age. For manufacturers, the manufacturing date is probably the starting point.

For any item which consists of more than one raw ingredient, it is also important to consider that each ingredient which was used to manufacture it also has its own certain shelf life. Similar products can be made with old or new ingredients, and the age of the ingredients may have some or no effect on the shelf life of the finished product; information about the ages of components may be of interest to consumers for aesthetic reasons, but it is unlikely to be provided other than in generalities such as "fresh cream" or "aged cheese".

How is shelf life indicated on a label?

There are several methods of indicating shelf life. Sometimes a date is specified; other times a usage period, such as "use or discard within two weeks after opening" is specified.

Many labels include a date, but this is only meaningful information if the date is correctly interpreted. Some labels show the date the item was manufactured. This makes it possible for the consumer to know how long the product has been on the shelf before purchasing it. This method is used for products with a relatively long shelf life where there is no concern about the product going bad for a long time or at all; dry foods such as grains, powdered milk, and packaged sugar or salt are good candidates for this approach. The problem with marking a package with its date of manufacture is that consumers are unlikely to know how to estimate the usable time remaining for the product, so the only use they can make of this number is to compare the manufacturing dates for every item on the shelf, searching for the youngest (most recently manufactured) one.

Another method is for the manufacturer to estimate an expiration date for the product, whereby the consumer knows how much time is left to use the product in the future but has no indication as to how far in the past the product was
manufactured, nor how long it may have been sitting on a shelf in a store.

Some labels will indicate how long a product can be used after opening. This method is good for products which normally have a long shelf life while their packaging remains sealed, but a relatively short life after the seal is broken: canned food and cosmeceuticals are likely to be in this category.

In the European Union, cosmetics are typically marked with a period-after-opening (PAO) symbol to show how many months after opening a product can be used "without any harm to the consumer". It's important to note that the claim here is that the cosmetic has not become dangerous, not that it has remained beneficial. In part, this is due to the definition of cosmetics as inactive: if they never could do anything, there is no reason to label them as if at a certain point their activity degrades. It's also consistent with the way fresh foods are handled, in that a vegetable that has become a bit soft or slightly brown is perfectly edible for a long period after it has lost some of its visual attractiveness; turn it into juice or soup, and it is enjoyable long after it has ceased to be beautiful. For botanical-rich cosmeceuticals, with a large portion of their ingredients subject to degrading in the ways plant material naturally degrades (changing color and texture, primarily), thinking about shelf life in this way can be particularly valid.

"Best by" dates also acknowledge the complexity of predicting how long a product remains usable. A "best by" date does not report a past milestone (manufacture date) and rely on the consumer to calculate whether excessive time has passed between that date and today's date. Nor does it make an absolute prediction about the future (expiration date), as if environmental factors such as excellent or inadequate storage could not extend or shorten the product's usable life. A "best by" date suggests that some non-specific quality of the item, something available when it is "best", degrades in a predictable-enough way that it may no longer be "best" after a time; it remains up to the consumer to decide whether a product is still "good" after it has ceased to be "best".

A "sell by" date is even more vague as to a product's actual age or its remaining useful life, suggesting only a time by which the item should be relocated from a shelf in the store to a shelf in the consumer's home. This can be useful information within a store as a means of distinguishing between last season's model and this season's new-and-improved model (perhaps because a buy-back guarantee will expire, or for some other administrative reason), but it is not meant to advise a consumer as to when a product can no longer be safely consumed.

For cosmetics distributed in the United States, the FDA's Cosmetic Labeling Manual does not require any indication of shelf life although it does require that the label identifiies the name and intended use of the product, names its manufacturer or distributor, specifies the ingredients and the quantity of finished material in the package, and provides any necessary warnings or directions. For other products such as drugs and nutritional supplements, product labels or inserts must include additional information as specified in the regulations for those products. Label space is tight, especially on the small packages often used for cosmetics, so manufacturers are unlikely to squeeze in anything that is not absolutely required.

How is shelf life estimated?

Shelf life is estimated by the manufacturer, possibly with the assistance of external laboratories which specialize in product stability testing. The natural method of estimating shelf life is to use the product in the way it is expected to be used by the consumer and observe when it starts to go bad, but this is practical only when it is expected to go bad within a short period.

Because it can sometimes take years for a product to break down, accelerated stability testing shortens the testing period by exposing a product to extreme stress: for example, material can be exposed to high heat for a short period rather than low heat for a long period. Of course, short-term exposure to extreme stress sometimes results in altering a product so that what is being tested has little resemblance to what consumers will actually use. Accelerated stability testing is most likely to be valid for materials that are primarily solid, such as steel construction beams or rubber automobile tires; it is least likely to be valid for materials such as foods and cosmetics, with contents naturally high in liquids that may respond to high heat by becoming cooked rather than by demonstrating their normal aging processes.

What happens after shelf life ends?

Entropy increases: unprotected from the laws of physics, any complex structure tends to break down with the passage of time. After a product is manufactured, it begins to decay; the goal is to control (or at least predict) the rate of decay to allow a reasonable time for the intended use of the product. For different products, reasonable use time is different, ranging from a few days for fresh fruit to many years for canned fruit.

As products age, they can oxidize; anti-oxidants have been used as preservatives for a very long time to slow down the rate of oxidation. As oils age and oxidize they become rancid, acquiring a strong and pungent smell. Many ingredients turn dark brown as they age, though for some ingredients that is their natural color and not an indication of oxidation and aging.

Preservatives, like other ingredients, have their own aging processes and do not work indefinitely: as time passes, preservatives lose their efficacy in fighting against proliferation of bacteria or fungi and the product can become
contaminated.

Many cosmetics are formulated as emulsions, with naturally-separate oil and water phases combined by chemical or physical means. Separation can be a sign that an emulsion is reaching the end of its useful life, though it is also true that phase separation can be an inherent feature of a product and not a sign of breakdown.

Oxidation and loss of bacterial protection are results of chemical decay. Physical decay can be a sign of an aging
product, demonstrated by phase separation when this is not an intended feature of the product, such as when oils separate from the emulsion phase as free oil and not as part of the emulsion. Gravitational separation of emulsion particles which float up or settle down depending on their relative densities is not a sign of decay when emulsion droplets are intact. In such cases the label will advise the consumer to "shake well before use".

So, a product's shelf life is determined by its chemical and physical shelf life which also depends on supporting ingredients which can extend final shelf life.

At the end of its shelf life, a product no longer meets the standards set for it by its manufacturer. It should be discarded at this point. A medicine may become unsafe to use. Food may lose some of its nutritional value, and a cosmetic may lose some of its skin-protective value; both may become rancid or bacteria-infested.

Are there any ways to increase shelf life?

Yes; many choices in the processes of formulating, manufacturing, packaging, storing, and using a product contribute to extending or shortening its shelf life. Not all of these can be predicted by the manufacturer; even if a label indicates that a product's shelf life has not yet ended, consumers must be responsible for their own safety by making their own decisions about whether it should be used. The human senses of taste and smell provide us with highly-evolved tools for judging whether any material can be safely handled or consumed; if you don't trust it, don't use it.

Ingredient selection determines the outer limits of a formulation's shelf life. In addition to ingredients included strictly for the purpose of extending shelf life ("preservatives"), ingredients included for other purposes can make important contributions. In cosmetics, anti-oxidants included to provide anti-aging benefits to the skin can provide similar protective benefits to the skin care in which they are formulated. Similarly, anti-fungal and anti-bacterial ingredients intended to treat infections when a cream is applied to the skin can also prevent the growth of contaminants within the cream itself. Long-standing preservation methods for foods rely on ingredients such as salt (for pickling) and sugar (for jellies, jams, preserves, and candies) that prevent decay but alter the texture and flavor of the main ingredient. Many low-quality skincare products have extremely long shelf lives because they consist largely of mineral oil or alcohol, neither of which are particularly good for skin but both of which are highly resistant to contamination and degradation. Mineral oil is the final stage of decay for dinosaurs; it cannot degrade much more!

Temperature control is usually an effective method of increasing shelf life. Refrigeration can extend shelf life, especially for material in open containers, because low temperatures impede chemical reactions and slow the growth of some bacteria. Refrigeration provides only partial protection from contamination: as most of us know from unpleasant personal experience, even in a closed container inside a refrigerator, mold will eventually grow. For some materials such as foods and single chemical ingredients, freezing can also be helpful; however, freezing is damaging to for water-based cosmetics because, when they are removed from the freezer, the process of thawing can cause their emulsion to de-formulate. Because this is such a key factor, many labels are marked with manufacturer's recommendations about temperature control such as "Refrigerate after opening" or "Do not freeze" or "Store in a cool, dry place"; if consumers do not follow those instructions, manufacturers' estimates of shelf life become invalid.

Protection from light is also often effective, which is why many cosmeceuticals, vitamins, and food products are packaged in opaque rather than clear containers. Protection from air, which is the primary oxidizer and also carries bacteria, mold, dust, and water, is also essential. Keeping a container tightly closed when it is not in use, and not opening a new container at all until it is ready for use, are simple steps that are completely under consumer control. For manufacturers, choice of packaging is the most important method of protecting a product from air. To help with this, "airless packaging" is sometimes used: as the skincare product is dispensed, an inner chamber pushes the remaining material into a smaller and smaller area to protect it from exposure to the air that would otherwise fill the "empty" space within the container. Use of such packaging can be a high-cost option, but the same philosophy can be followed by using some lower-cost approaches. For example, skincare should be packaged in a container no larger than is necessary for its contents; something as simple as packaging 2 ounces of serum in a 3-ounce bottle can cause the product to decay more rapidly than it would in a properly-sized container, free of contaminating air. For low-thickness serums and lotions, using a pump or spray to push material out of the container, rather than allowing fingers and air (both possibly contaminated) to enter the container and extract material, is also a way of using packaging to improve a product's protection from air. Packaging into single-application ampules or "ketchup packets" also addresses this: the packaging is destroyed at the first and only moment the product within is exposed to the air, so there is no possibility of re-closing the package with air inside.

After any product is unsealed, it should be used up quickly. When a container is opened for a quick sample then set aside for a long period, the product inside will age rapidly when compared to the same material in a container that has remained sealed during the same time. When you start using a product, it is least likely to be wasted if you use it up continously and without large gaps between uses.

Protection from water is also important, for some of the same reasons as protection from air. Also, water dilutes preservatives and supports the growth of bacteria and mold, which is why, when a container becomes partially empty and a consumer adds water to "stretch" the remaining material, the shelf life of this new, diluted material is greatly reduced from that of the original formulation.

Refrigerated for 3 months in a flexible plastic container, cooked shredded carrots are mold-free where the plastic lid was pressed into direct contact with the carrots but mold-infested where pockets of air exist between the carrots and the lid.	A side view of the same container shows that mold has spread downward into loosely-packed areas where carrots are interrupted by air pockets.

Formulators can influence potential shelf life by choosing the right ingredients, as packagers can make an impact by using approriate packaging. Manufacturers can provide key help to consumers by providing clear instructions about how to store and use the product. Consumers can influence actual shelf life by keeping containers closed, following manufacturers' storage instructions, and using their own good judgement about protecting materials from damage and contamination.