Why would you want to add preservatives?
Whenever you mix cosmetics that contain water, you’re creating a mixture where microorganism can live and multiply.
Isn’t it enough to work cleanly?
It is a good practice to work cleanly and desinfect your tools before using them, but you will not be able to create cosmetics completely free of microorganisms. You cannot sterilize cosmetics.
If you however do want to avoid preservatives, you can put the cosmetics in a fridge. The lower temperature makes microorganisms to grow slower. A cream may last up to a couple of weeks in there.
The group of parabens are commonly used in commercial cosmetics. They are cheap in industrial quantities and very effective against bacteria and fungi.
Some people however do have allergic reactions to them.
Usage concentration: Between 1-2,0% in creams for 3-6 month.
Biokons Plus contains Trideceth-8 which acts fungicidal and Caprylyl Glycol which act as bactericide, and Phenethyl Alcohol.
Usage concentration: Between 0,5-2,0% in creams for 2-6 month. In pure water mixtures up to 0,6%.
Usage concentration: Between 0,5-1,0% for 6-12 month