Preserving Homemade Herbal Creams and Syrups

Have been wildcrafting for a few years and have started making my own creams and ointments as well as facial cleanser and cough and cold tonic. One problem - very short shelf life unless refrigerated. I understand benzoin can be used as a stabilizer but how much and are there any side effects? Also if I wished to add plant properties to a commercial shampoo, would I use infused oil or tincture? I don't have the money or patience to get into distilling essences.

Benzoin tincture is used as a preservative for creams. Add a few drops for each 250 grams of cream or ointment. Benzoin would add its antiseptic action to the cream. Optionally, you can add the contents of two to three 400 iu vitamin E capsules. Vitamin E is a preservative that is nourishing to skin tissue.
Propolis is another antiseptic preservative: mix one part of propolis powder to 10 parts of oil in making a cream or ointment.
Glycerine can also be used as a preservative in creams: 1 part glycerine to 6 parts cream.
Olive oil naturally resists rancidity, so is a good base for making creams and salves
Honey is a good preservative for cough syrups. The ratio is 500ml of herbal infusion or decoction to 500 g honey. Honey is soothing and antibacterial. The cough mixture must be sealed with a cork, as a screw top can explode if the syrup ferments.
Herbs should be added to shampoos in the form of strong infusions or decoctions. The alcohol in tinctures can dry out the natural oils in the hair. Add 2 tablespoons of the herbal infusion or decoction for each cup shampoo.