There are three forms of mercury which can harm the body through mercury poisoning and other different ways:

1. Inorganic mercury
2. Elemental mercury
3. Organic mercury

What can cause mercury poisoning in humans:
The effect that exposure of mercury have on people depends upon the amount of mercury, the duration of exposure, the measure of exposure, the age of the person and the general health of the person.

1. Organic Mercury poisoning from fish consumption:
The U.S. EPA states that all organisms have trace amounts of methyl mercury (organic mercury) in their tissues. Rain causes methyl mercury to spread into river bodies. This methyl mercury is collected in the tissues of freshwater and saltwater fishes. Consumption of these fishes leads to exposure to methyl mercury in humans. If this exposure continues for a period of time then it can cause serious health issues. Pregnant women who have contaminated fish may face the risk of damaging the brain of the fetus over time.

2. Inhaling elemental mercury vapors:
The metallic mercury and elemental mercury causes health issues if inhaled in vapors form and it reaches the lungs. Elemental mercury inhalation happens when products having this mercury spill in closed indoor places that are warm. On the contrary, touching or eating elemental mercury is not harmful and the metallic mercury does not stick on the skin or get absorbed by the stomach. The metallic mercury poisoning occurs when it is inhaled. The symptoms of metallic mercury inhalation are very prominent. They include puking, trouble in breathing, severe cough, and strange metallic taste in the mouth, loss of appetite bleeding gums and swelling in the gums(gingivitis). If you inhale large amounts of mercury then it can cause serious health problems like brain damage and lung damage and even death in extreme circumstances.

3. Swallowing of inorganic mercury
If you swallow inorganic mercury it can cause mercury poisoning. Inorganic mercury can be found in chemistry labs, batteries and in several disinfectants. If you accidentally swallowed inorganic mercury then it can cause serious health problems like damage to the alimentary tract, kidney damage as well as damage to the nervous system. The extent of damage depends upon the amount consumed. The symptoms of inorganic mercury poisoning may include burning sensation in the throat and stomach, puking and bloody diarrhea.

Other health issues faced:
Apart from the health issues mentioned above along with the kind of mercury poisoning causing them there are more health concerns that your should know about.
Acrodynia: also referred to as the Pink’s disease. This is more commonly observed in children who have been exposed to any form of mercury. The skin of those suffering from this disease starts to peel and the hands turn pink in color. The children have also shown other symptoms of mercury poisoning like, irritability, leg cramps and learning disorders.

Cases of Mercury poisoning:
1. Jeremy Piven (actor) was diagnosed with hydrargyria caused by mercury poisoning, from eating sushi twice a day for almost twenty years.  (December 2008)

2. Karen Wetterhahn, a chemistry professor at the Dartmouth College accidently spilled a little dimethylmercury on her latex glove on 14 august 1996. She developed symptoms of mercury poisoning after five months. She tried chelation therapy, however, died of brain malfunction.

3. An episode of Mercury poisoning took place in rural region of Iraq in 1971-1972. The grains treated with a fungicide (methylmercury based) were to be planted, but were used to make bread. It resulted in as many as 6530 cases of reported mercury poisoning and 459 deaths.