The health effects of mercury are: If mercury is separated from broken thermometers it can enter the body through respiration as a flexible metal or skin and can cause various diseases in the body if present in large quantities. Mercury is a very toxic metal and can cause skin irritation, skin rashes, allergies. It can cause headaches, can damage the nervous system. It can cause genetic defects and mutations in human genes. It can affect reproductive health. Other side effects of mercury include vision distortion, memory loss, and muscle damage, as well as muscle instability.