There are different types of mercury, depending on the structure of the mercury molecule. Every type has its different properties and is therefore utilized in different ways in dentistry, medicine and industry. Allergy to mercury is specific, meaning that an individual can be allergic to one specific type of mercury and not another. This is because the cells involved in the so-called Type IV allergic reaction – the memory cells – depend on the exact structure of the molecule to be activated. Naturally, it is possible that an individual can be allergic to all four types of mercury. In many cases it is important to locate the source of exposure to mercury that causes inflammation in the body, so that exposure can be stopped. The MELISA test can differentiate between allergy to each of the four types of mercury.
Inorganic mercury, or ‘metallic mercury’, is a frequent source of metal allergy. It constitutes 50% of dental amalgam fillings. Dental authorities accept that mercury vapour constantly evaporates from the fillings, but argue this is below a safe limit. However, for hypersensitive patients, there is no safe limit. Replacing amalgam fillings with ceramic substances has delivered radical improvements in patients who tested MELISA-positive for mercury. In the body, bacteria can transform inorganic mercury into the organic form methylmercury.
Methylmercury is the most toxic form of mercury. It affects the immune system, alters genetic and enzyme systems, and damages the nervous system, including coordination and the senses of touch, taste, and sight. Methylmercury is particularly damaging to developing embryos, which are five to ten times more sensitive than adults. Methylmercury survives up the food chain, so the large fish at the top of the food chain such as shark, swordfish and large mouth bass have the highest concentrations. It is distributed evenly across fish, and is not affected by cooking. This form of mercury is also found in contaminated soil and grain. Bacteria in the body can transform inorganic mercury into methylmercury.
Phenylmercury is the organic mercury most commonly found in dental root fillings. While it has been phased out in many countries, it is also used as a preservative in eye drops and nose drops. Phenylmercury is used to control the growth of fungus in some interior latex paints manufactured before 1991, some exterior and oil base paints, some caulks, eye-area cosmetics, toiletries and other products.


Ethylmercury is a form of organic mercury. It forms a part of thimerosal, which is used as a preservative in vaccines, eye drops and nasal sprays.

Thimerosal is one of the most controversial substances is modern medicine. Its main component is ethyl mercury (49.6% by weight), yet it is still used as a preservative in some child vaccines, flu vaccines and some eye drops and contact lens solution. It is being withdrawn from vaccines in many countries. It is the subject of a lawsuit in the US filed by parents of autistic children who believe it to be responsible for neurologically damaging their children. Its use is defended on the ground that the amount of mercury is too small to pose danger. But to those who are hypersensitive, even trace amounts can create health problems.
Full body autoradiograph
A special form of mercury can be used to demonstrate that mercury binds to the body proteins. The distribution of mercury in various organs of the body can be traced by sensitive photographic emulsion. Below are four pictures of mice that were injected with mercury labelled with a radioactive isotope. Then, using autoradiography, a special picture was produced. The areas where the mercury is deposited are shown in white.
The pictures demonstrate widespread distribution of mercury in the body of the mice. Organs rich in fat – such as brain and collagen – are very prone to mercury binding. One of the reasons for this is that mercury is particularly keen to bind to two amino acids; methionine and cysteine. Both amino acids contain sulphur hydrogen (SH)-groups. This is a particularly attractive target for mercury. Fat tissues and collagen tissues are rich in SH-groups.

Figure 1. Distribution of radioactivity in male mouse 6 hours after intravenous injection of 203HgCl2. Magnification 2x.

Figure 2. Distribution of radioactivity in male mouse 24 hours after intravenous injection of 203HgCl2. Magnification 2x.

Figure 3 and 4. Distribution of radioactivity in male mouse 2 days after intravenous injection of 203HgCl2. Magnification 2x and 9x (right).

Pictures are from “Explorative study of tissue distribution of 203Hg2+ in mouse after oral administration of some chelating substances with and without vitamin C”, by Anette Seo, Safety Assessment, Astra AB, Södertälje and Institute for Pharmaceutic Bioscience, Department of Toxicology, Uppsala University, 1994. Thanks to Dr Anette Seo for permission use the material.