Among the forms of mercury present in nature, methylmercury is the most easily absorbed.
Among the forms of mercury present in nature, a majority of methylmercury gets absorbed from the digestive tract (small intestine). In contrast, only a few percent of inorganic mercury salts get absorbed that way.
Methylmercury, bound with a type of amino acid called cysteine, has a property of getting easily absorbed from the digestive tract and then penetrating into various parts of the body. Therefore, it can also make its way inside the brain and damage nerve cells, or cross the barrier of the placenta that connects a fetus with its mother, eventually entering the body of the fetus as well.
Metallic mercury, which hardly gets absorbed from the digestive tract, is easily vaporized and nearly 80% of inhaled metallic mercury vapor gets absorbed from the lungs. Depending on the volume absorbed, this may cause poisoning. There are examples of cases overseas that relate to exposure to vaporized mercury used in the process of gold mining.