Disgust is an emotional response of revulsion to something considered offensive, distasteful, or unpleasant. Many researchers have theorised that the emotion of disgust has evolved as means of protecting us from disease. Disgust appears to be triggered by objects or people who possess particular characteristics that signify disease, such as:

body products (feces, urine, vomit, sexual fluids, saliva, and mucus), foods (spoiled foods), animals (fleas, ticks, lice, cockroaches, worms, flies, rats, and mice), hygiene (visible dirt and 'inappropriate' acts [e.g., using an unsterilised surgical instrument]), body envelope violations (blood, gore, and mutilation), death (dead bodies and organic decay) or visible signs of infection.

Based on information from WikipediaAPA Dictionary of Psychology
All Emotions (56)