Xanthan Gum

Even the most "natural" and "free" bottled salad dressings usually have Xanthan or Guar gum on their ingredient lists, and even though they sound funny, they're perfectly natural. Both help to thicken and emulsify oil-and-vinegar mixtures to keep them from separating.
- Natural Choices Magazine 2015
BUT...keep in mind that Xanthan gum is usually processed with corn and Guar gum can act like a laxative.