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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.
However, although alcohol can increase the chances of thread veins, experts say they can also be caused by too much sun, smoking, or by rosacea, a skin condition which causes a red nose and face. 1  Soaring numbers of men are having unsightly thread veins - caused by drinking, smoking and sun exposure - removed.