Back in 2002, the International Agency for Research on Cancer, which is part of the World Health Organization, looked at all the published studies on low-frequency magnetic fields and cancer. They classified these fields as possibly carcinogenic to humans. The main reason was a pattern in studies of childhood leukemia. Several large pooled analyses had brought together data from many individual studies across different countries. These pooled studies found that children who lived in homes with the highest measured magnetic fields had about twice the risk of developing leukemia compared to children in homes with very low fields.
But these were what scientists call observational studies. They do not prove cause and effect. The researchers could see an association, but they could not rule out other factors that might explain it. For instance, children with higher measured fields might also live in homes with different wiring, different traffic patterns, or different mixes of other exposures. The studies tried to control for these things, but you can never control for everything. Also, the number of children in the highest exposure group was very small. Very few homes actually have magnetic fields that high. This makes the statistical link fragile.
The IARC rating of possibly carcinogenic means there is limited evidence in humans and less than sufficient evidence in animals. It is not the same as saying the fields cause cancer. It is the same category used for things like coffee and pickled vegetables. The rating is a signal for more research, not a clear danger warning.
Understanding the numbers helps. Magnetic fields from power lines and household wiring are measured in milligauss in the United States. One large survey of nearly a thousand American homes found the average room-by-room reading, away from appliances, was under one milligauss. Right next to a big transmission line carrying its usual load, the field can be in the tens of milligauss. But it drops off fast as you walk away. Inside a house, the surprises often come from the wiring, not from the line outside. A circuit where the outgoing and returning currents do not cancel can raise the field across a whole room. A licensed electrician can trace and fix that.
For comparison, the international reference level for public exposure to these fields is 2,000 milligauss. That is far above anything normally found in a home. The studies that showed the link to childhood leukemia involved average exposures above about 4 milligauss. Even at that level, the evidence does not show that the field itself causes the disease. The studies cannot separate the field from everything else that goes with living near certain kinds of power lines.
If you are worried about your child’s health, the right person to ask is a doctor. If you have questions about the wiring in your home, a licensed electrician can help. If you are concerned about a nearby power line, your utility company can give you information about the line’s construction and load. The Federal Communications Commission handles radio-frequency exposure, not these low-frequency fields. The science on power line fields and childhood leukemia remains uncertain. That is what the IARC classification means. It is not a verdict. It is a call for more study.
More notes on this topic are at power lines and childhood leukemia.