Milk borne diseases are any diseases caused by consumption of milk or dairy products infected or contaminated by pathogens. Milk-borne diseases are one of the recurrent foodborne illnesses—between 1993 and 2012, over 120 outbreaks related to raw milk were recorded in the US, with approximately 1,900 illnesses and 140 hospitalisations. With rich nutrients essential for growth and development such as proteins, lipids, carbohydrates, and vitamins in milk, pathogenic microorganisms are well nourished and are capable of rapid cell division and extensive population growth in this favourable environment. Common pathogens include bacteria, viruses, fungi, and parasites, and among them, bacterial infection is the leading cause of milk-borne diseases.

Despite the popularity of pasteurisation in modern days, the risk of contamination cannot be eliminated. Infection can turn milk into an optimal vehicle of disease transmission by contamination in dairy farms, cross-contamination in milk processing plants, and post-pasteurisation recontamination.

Symptoms of milk-borne diseases depend on the amount of pathogen ingestion, time of pathogen incubation, and individual variations like the patient's susceptibility, age, and pre-existing medical conditions. Generally, milk borne diseases are not life-threatening, and taking medications like antibiotics and over-the-counter drugs helps relieve symptoms. Typical clinical signs are fever and mild gastrointestinal disturbance, including diarrhoea, nausea, vomiting, and abdominal pain. Nevertheless, severe complications can be fatal and are often observed in young children, aged individuals, and immunocompromised patients.^{[citation needed]}

In the 19th-century United States, the urban milk supply was regularly diluted and contaminated by dairymen, dealers, and retailers. The public health harms from milkborne diseases prompted localities in the U.S. to enact minimum quality standards for milk and hire milk inspectors. According to a 2025 study, this was associated with a substantial decline in deaths from diarrheal diseases and typhoid.

There are three major routes of infection and contamination of milk:

Salmonella can survive within 5.5 °C to 45 °C with high sensitivity to acid and are more commonly found in unprocessed milk. Owing to the sensitivity to pH, Salmonella have different survival rates in different dairy products like cheese under different storage temperatures. In ripening Cheddar cheese, they can survive for several months at 13 °C but most fail to survive for more than 36 days in Domiati cheese. Most Salmonella strains are pathogenic, especially S. enterica subsp. enterica which accounts for 99% of human infections and can bring about salmonellosis.

Salmonellosis is induced by infection of Salmonella with a swift onset of disease 12 to 36 hours after consumption of contaminants and can be clinically classified into three types, namely enteric fever (also Typhoid fever), gastroenteritis and sepsis. Enteric fever usually has 7 to 14 days of incubation with mild symptoms like malaise and headache. In rare cases, the body temperature of the patients can surge up to 40 °C, rendering them delirious. Gastroenteritis has a much shorter incubation period than enteric fever (usually 3 to 72 hours) and shows common gastrointestinal disturbance symptoms characterised by watery faeces with an unpleasant and strong odour as well as blood and mucus. Sepsis can lead to serious complications in various organs, in particular arthritis in joints. A recent case of a large-scale salmonellosis outbreak was reported in Iwamizawa, Japan, in 2011 because of contamination in school meal processing facilities, affecting over 1,000 students and school staff at nine local Japanese schools. The majority of affected individuals had acute diarrhoea, and 13 of them were hospitalised.

The preponderance of reported milk-borne diseases arises from Campylobacter, most notably the strains C. jejuni and C. coli. Campylobacter is implicated in more than 80% of reported American disease outbreaks from raw milk from 2007 to 2012. Aside from the US, the UK also recorded around 59,000 confirmed cases of campylobacteriosis triggered by raw milk consumption in 2016. As thermophilic strains, C. jejuni and C. coli can grow between 37 °C and 42 °C and they have a high biological activity rate inside host animals. C. jejuni, the predominant pathogenic strain, is found to have a noteworthy genetic variation that allows them to develop diversified phenotypes, for example high resistance to temperature fluctuations during pasteurisation and anti-bacterial agents in animal hosts, and improve their adaptability to changing environments in dairy products.