Any cosmetic product that contains water (the source of moisture) needs a preservative to extend its shelf life. Without a preservative the product would go off within about two weeks; a week or two longer if it’s in the fridge.
If you want to produce products for commercial use you have to use preservatives to one degree or another because there can be quite a long lag between your product being produced, landing on a store shelf and eventually reaching someone’s bathroom. Even once the product gets to the end user it may take a few weeks or months before they use it. For instance I buy some of my favorite products in bulk and it can be many months before I get round to the final bottle.
Ideally two to three years.
Importantly, note that whilst most products may have a 2 to 3 year shelf life from the time of manufacture, once opened this lifespan can be as short as 30 days and at most 12 months. It’s generally advisable to throw away any beauty products that have been open for a year.
How much preservative should you use?
It depends. Rinse-out products such as shampoo require a different concentration of preservatives than leave-in products. The longer you want the product to last the more preservative you will need to use.
The preservative manufacturer’s Material Safety Data Sheet (MSDS) will provide the acceptable usage rates. That is, the quantity of preservative that you should use. Importantly, keep in mind that different preservatives have different usage rates.
Use enough preservatives to prevent the growth of microbes but not so much that they cause skin irritation, allergic reactions, product instability and other negative side effects.
Do some research to ensure that your particular preservative won’t cause too many allergic reactions (not that everything is prone to creating allergic reaction so you can't avoid this), that it works well with all your other ingredients and that it operates efficiently within the pH range that it needs to operate. The perfect preservative should not cause a change in the color or smell of your product. In addition read up on any regulations covering it, e.g. in Europe some preservatives are banned or their usage is heavily regulated.
I have opted for optiphen and a preservative that is a mix of Phenoxyethanol & Ethylhexylglycerin.
Only in certain products, e.g. water-free hair butters and oils is that possible. For all other hair products that need to contain water such as shampoos, conditioners, detanglers and moisturizers you cannot avoid using preservatives if you want the product to last more than a couple of weeks. Preservative-free products rot quickly and require constant replacement.
Any product that claims to be “Preservative Free” is either harmful or outright mislabeled; they simply mean they are using more natural preservatives. Even then, natural alternatives offer limited protection against bacteria and as such need to be combined with other preservatives for full preservation of the product.
There is no evidence at all that preservatives are harmful and if you use them in the right quantities they will help your products last much longer without causing any negative side effects.
Whether you use preservatives to prolong the life of your product or not, always store your bottles in a cool dry place.
You might also like:
- August 21, 2012 issue of Manila Bulletin, Lifestyle Section. Author, Fred C. Reyes (CEO of SkinStation).
- Yazar K, et al. Preservatives and fragrances in selected consumer-available cosmetics and detergents.
- Brandin H, et al. Adverse effects by artificial grapefruit seed extract products in patients on warfarin therapy.
- von Woedtke T, et al. Aspects of the antimicrobial efficacy of grapefruit seed extract and its relation to preservative substances contained. Pharmazie. 1999 Jun; 54(6):452–6.
- Preservatives: Imidiazolidinyl and diazolidinyl urea (SwiftCraftMonkey)
- Germall Plus (lotioncrafter.com)
- What Is Diazolidinyl Urea? (wisegeek.com)
- Germben II (web.archive.org)
- Potassium Sorbate (wikipedia.org)