Sometimes we need to use synthetic ingredients to help with the formulation, we never use nasty ingredients, only safe ingredients for skincare. 
Ingredients affecting 100% Natural Claims and what they do:

Phenoxyethanol is a widely used synthetic preservative that has global approval for use in all cosmetic products in concentrations up to 1%. We stick to below this level.

Sodium Benzoate is a salt of Benzoic Acid that is found naturally in cranberries and apples and is used as a preservative.

Potassium Sorbate is used as a preservative, almost always used in conjunction with other preservatives like Sodium Benzoate.