Traditionally as an adaptive function, disgust has served for disease avoidance. In other words: to keep us healthy and to keep us from getting ill. Our feeling of disgust works incredibly well for us to tell us to avoid, for example, faeces, rotting meat, or parasitic infected food.
If we have a "disgust" response to something, typically it's associated with fear. However, fear and disgust are very separate and unique emotional functions within the limbic system and they definitely result in different facial expressions. For example if you're experiencing fear, your eyes might go wide, and your heart rate may either increase or decrease. Disgust on the other hand may result in a bit of a lip curl, or a feeling in the pit of your stomach that says "don't go near that or you might get ill!".
Link to study: http://rstb.royalsocietypublishing.org/content/366/1583/3478