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Thick blood may also be caused by the presence of harmful pathogens such as fungi, viruses, bacteria, and parasites. These pathogens can actually activate a coagulation response in the body as a way to avoid being attacked by the bodyâs immune system.
Cancer can also cause blood thickening. Not all blood clots are caused by thick blood. Blood clots leading to heart attacks and strokes can be formed when thin blood comes into contact with plaque, which triggers a blood clot. Some blood clots result from sluggish blood flow or poor circulation.