The rapid advance and increasing complexity of medical science
Manure is a common contaminate usually during the growing process of plants (especially because of use as fertilizer). Pesticides can also contaminate food both when grown or during processing, especially when not separated from things like rat poison. Human hair can contaminate food in both ways, but it also get into food during preparation if not in a hair net. <span />
Inheritance or your genes. If anyone in your family has a chronic disease you may be at risk of getting that disease.
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A.) using damaged equipment as long as possible before replacing it