Methylmercury is a neurotoxin

Methylmercury is a neurotoxin, a substance that damages neurons. The primary pathway of methylmercury into humans is through eating methylmercury-contaminated fish. Concentrations of methylmercury in fish are not reduced by cooking, frying, or baking. If methylmercury-contaminated fish are consumed in high quantities by a pregnant women or children, methylmercury can damage nerve cells and prevent the brains of fetuses and children from developing in a healthy way.

Why is methylmercury so hazardous to unborn humans?

After fertilization of the egg, the newly formed human zygote has no nerve cells. But after a few weeks of development, the brain starts to form and by birth, a baby’s brain is thought to contain about 100 billion nerve cells, roughly the total number of nerve cells the brain will ever have. This development of billions of nerve cells and the trillions of connections between them is essential to becoming a healthy infant and eventually an adult. Methylmercury in fish can negatively affect the central nervous system, particularly the developing brain of a fetus.

Egg to Infant

Fish can still be an important part of the diet

According to the U.S. EPA, fish provide protein, are low in saturated fat, are rich in many micronutrients, and provide certain omega-3 fatty acids that the body cannot make and are important for normal growth and development. The U.S. EPA and FDA have concluded that the following groups of people can derive important developmental and health benefits by eating fish that are low in mercury:

  • Women of childbearing age (about 16-49 years old)
  • Pregnant and breastfeeding women
  • Young children

For more information, go to

Click here to find out more information about how to estimate mercury in fish or for information about fish consumption advisories.