Determining the Shelf Life of Your Products
A product’s shelf life is the range of time a product, stored following the specific instructions by the manufacturer, will be usable. Since this is a broad description, it can be interpreted in multiple ways, however, in our industry, it’s tied to a formula breaking over time, or bacteria or other undesirable build up. In either case, knowing and testing for accurate shelf life is crucial. We’ll go over three options for testing your own products.
The realities and constraints of Shelf Life
Knowing how long you need your product to last is key information for your formulation team. Knowing where the product is used — geographically as well as what room in the house — is only one component. You’ll also want to be aware of how much safety stock you think you need, what the lead times for production are, as well as what your customers will expect. Sell-through time will also affect your shelf-life need, as well as the ingredients themselves. For instance, an anhydrous serum will have a shorter shelf life than an emulsion with a preservative system. Why? Because the oils themselves will determine the shelf life and while the addition of Vitamin E and Neem and other anti-oxidants can help extend them a bit, nature is going to dictate how long an oil will retain its color, freshness, and benefits. If your formulation team knows you’re looking for a 6 month, a 12-month or 18-month shelf-life, it will guide the ingredient selection.
When you develop a product, one of the first things to forecast its success is how long it will take a customer to use their product before a repurchase. One month? Three months? You can manipulate this to get the optimum balance by selecting the size – 8 oz for a body wash vs. 1 oz for a serum. If you’re selling a daily product – like a facial cleanser or toner, then you will have faster repeat business than something like a mask that might be used just once per week. Then you need to consider how the customer will store the product: in a wet bathroom, a gym back, the glove box of a hot car, will your product be used professionally in a temperature-controlled spa. Once you know and understand the environment your product will experience, you can think about shelf life requirements. Remember, too, you’ll need to factor in sell-through at your retailers/distribution center, and safety stock (how much stock you have on hand over the orders you have to fill) Safety stock is critical so as to not get caught short between production runs.
With all those factors in mind, you can get a good handle on the shelf-life you think you need.
That said, however, the official expiration date can be set only once you’ve tested the shelf life of your product, but not before. It’s easy to think you’ve been using your product reliably for a few months now and it’ll do great, without really “testing” the product. Don’t get caught up in this trap only to be met with an unpleasant stability issue in 6 months time once your product is on shelves! Product recalls are very expensive and can ruin your business before you get started.
Waiting it out
Real life, shelf life testing is the only TRUE way to know how a product will react over time. And, too, this is probably the most inexpensive (upfront) option there is, but it’s quite time-consuming. Just create what you want and then monitor a sample — keep one sample in glass and one in your final packaging for best results. This is truly the only way to know the exact shelf life. For example, if I make a lotion, and I want its shelf life to be two years, I’ll be getting acquainted with a sample of it and monitoring it for the next two years. On top of sharing my morning coffee with it every day for 730 days (unless there’s a leap year), I’ll have to accurately track and analyze data that suggests the formula is in good working order. This includes photos, and detailed notes of observations about the look and stability of the lotion, as well as bacterial assays and pH testing.
One thing to keep in mind though is the term “low cost.” Although there is a limited output of money in this wait-and-see method, it costs you in terms of time spent monitoring and waiting to enter the market. If this is something that your patience and business can handle, it might not be a bad option that’s relatively cheap.
Controlling the hands of time: challenge & stability testing
Another great way to test shelf life is by doing stability testing or accelerated stability studies. In most cases, this is something you outsource to a 3rd party testing company, since buying your own Thermo Microbiological Incubator is around $5,000. And, this is just one of the tools a stability testing laboratory uses. In these labs, they have the resources to accurately test a product’s shelf life within a shortened amount of time. It’s basically an expedited test that takes three months to give a one-year shelf life, six months to give a two-year shelf life, and nine months to give you around three years of shelf life.
In accelerated stability testing, a product is stressed to test its degradation point (or rate) regarding high temperatures, moisture, light, agitation, gravity, pH, and packaging. When the activation point (or rate) is known, the degradation rate at low temperatures may be projected from those observed at “stress” temperatures. Then the in-between amount of time will give you the estimated shelf life. A product that’s expected to last three years without becoming unusable, can be sent off to a lab. This then turns your three years of wait time into a $500-$4,000 up-front investment with only nine months of waiting.
Using addition in chemistry
Another alternative is to estimate the shelf life dependant on the individual chemicals used. Calculating the ingredients with their actual known shelf life and taking the ratios of the ingredients in the product. This is not an ideal method because the chemicals change when combined; so results can fluctuate. Also known as Retained Sample Stability Testing. This method allows you to launch a product immediately. You’re simply guesstimating based on the molecular makeup of its ingredients. Again, assuming these compounds will change when combined, it’s not the most reliable method. But it does allow you to retain samples to accurately test while the product is out. For example, if a product has a shelf life of 5 years, it is conventional to test samples at 3, 6, 9, 12, 18, 24, 36, 48, and 60 months. Upfront costs for testing are virtually nonexistent, and it also allows you time to make money while still testing. However, the risk of it not living up to its expectations can be high.
Testing is tedious but necessary
Although this article outlines detailed procedures in various shelf-life tests, these tests are a crucial part of following regulations and producing safe products. Shelf life testing lets you provide an expiration date for your products. You may also find that the results may set you back or require a change of plan. Better to know up front so you can make changes before you get to market.
If you work with a Contract Manufacturer such as Essential, we perform our own initial stress testing and real-time testing studies to give us an early indication as well as an over-time study. However, we also use and highly encourage advanced challenge testing with third-party partners. This is a required step for products being sold throughout the EU and with some distributors here in the US. We’re happy to use our years of knowledge to further your business and guide you to the correct shelf-life data and choices. We’d love to help, and let us know what your most common stability issues are in the comments below!