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Thick blood is caused by a variety of conditions, such as heavy proteins in the blood, too much blood in circulation or a blood clot system imbalance, according to Southeastern Medical Oncology Center. Diseases such as cancer and lupus can also lead to thick blood. Continue Reading.
Chemotherapy also causes the immune system to overreact and excessive phlegm is often the result. Food allergies are known to cause excessive phlegm and certain types of food such as dairy products cause a thickening of mucous. Postnasal drip also commonly causes excess mucus at the back of your nose and throat many times after eating.