- The type of formula and its ingredients (whether it contains water, biological ingredients etc.)
- The circumstances under which your product has been produced (in other words how well your containers and tools haven been disinfected)
- The storage conditions (temperature, sun exposure, humidity)
- Whether you use your fingers to take out the product (fingers contain bacteria) or whether the product will be dispensed "finger-free" (e.g. through a pump, disk dispenser, or airless pump).
A shelf life can only be roughly estimated and should therefore always be tested using bacterial stability testing. If manufactured under very clean conditions, a cosmetic product preserved with a broad-spectrum preservative usually has a shelf life of 8-24 months, whereas a product preserved with natural antimicrobials about 2-4 months.