Disperse systems have been broadly classified as systems in which one substance, the dispersed phase, is distributed throughout another substance, the continuous phase or vehicle. They are important to pharmacy because of their widespread use. Pharmaceutical dosage forms that can be classified as disperse systems are suspensions, emulsions, creams, ointments, pastes, foams, suppositories, and aerosols. These dosage forms are used for many routes of administration (e.g., oral, dermatological, ophthalmic, parenteral, respiratory, and rectal). Depending on the route of administration, the disperse phase may vary in particle size from less than 1 μm for inhalation and ophthalmic use, to about 10–100 μm for dermatological use, and up to 200 μm for oral use. A small particle size will hasten dissolution and also reduce the chance of abrasion to susceptible tissues.