Parasites are microorganisms that live off of other organisms, or hosts, to survive. Some parasites don't affect the host. Others grow, reproduce, or give off toxins that make the host sick resulting in a parasitic infection.
Obesity is defined as having a body mass index (BMI) of 30 or more. BMI is calculated using a person's weight and height. It can lead to other conditions like diabetes, heart disease, and cancer.
Nicotine addiction occurs when a person becomes addicted to nicotine, which is a chemical found in tobacco. The addiction is physical, mental, and behavioral.