We know that while the number of people who contract serious illness from spit or chew tobacco may be fewer, those diseases (such as head and neck cancer) can be even more painful, disfiguring and ultimately lethal. While you may not be at risk for exactly the same tobacco-related illnesses, you are setting yourself up for: leukoplakia (white lesions which can be pre-cancerous); stained teeth, tooth decay, gum disease, bad breath and black hairy tongue; mouth and throat, esophageal and pancreatic cancer; heart disease and stroke; and ulcers and gastrointestinal distress.
Smokeless tobacco leads to nicotine addiction, sometimes at higher levels than cigarettes. It can increase risks for early delivery and stillbirth when used during pregnancy and can cause nicotine poisoning in children.
Smokeless Tobacco: Health Effects. http://www.cdc.gov/tobacco/data_statistics/fact_sheets/smokeless/health_effects/index.htm