Housefly larvae breed in accumulations of waste, garbage and manure. Adult flies, which often use buildings for shelter, feed on human and animal food and waste material. If undeterred, they commonly fall into and contaminate people's food. They also land on the exposed skin of people and animals. These habits potentially lead to disease transmission.

While houseflies are not necessary for the transmission of several important diseases and are rarely the most important agents, M. domestica is one means of transmission under conditions favorable to the flies. The intestinal diseases, which can be transmitted to humans, include:

Shigellosis - Bacillary dysentery and other diarrheal diseases.

Salmonellosis - Typhoid, paratyphoid, enteritis, food poisoning and others. While flies play a role in inoculating food with Salmonellosis-type microorganisms, they are generally less important here than in transmitting Shigellosis.

Cholera - Transmission by flies is possible but probably of minor significance.

Amoebic Dysentery - Flies may transmit cysts but this seems to be uncommon.

Parasitic Worms - Flies can carry eggs and cysts of many intestinal worms such as pinworm (Enterobius), roundworms (Ascaris), whipworms (Trichiuris), hookworms (Ancylostoma), tapeworms (Taenia, Dipylidium) and others may contribute to the spread of worms to people and animals.

Polio - Houseflies are able to transmit viruses such as Poliomyelitis and related viruses to human foods in quantities high enough to cause infection in some susceptible persons.

Eye Diseases - Eye diseases such as Trachoma (viral) and epidemic conjunctivitis (bacillary) can be spread by houseflies, Musca sorbens, found in Africa, Asia, and the Pacific, has an important role in spreading eye infections. M. sorbens is strongly attracted to infected eyes and feeds on eye secretions. M. domestica is also attracted to infected eyes but seems to be less important in disease transmission.