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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.
Excessive, thick phlegm or chest mucus can often be caused by viral or bacterial infections such as influenza, bronchitis and pneumonia, as well as irritants such as those inhaled during smoking. Chemotherapy also causes the immune system to overreact and excessive phlegm is often the result.