The evaluation builds on a systematic review of the research results. The IARC published its evaluation of research results in 2002 which concluded that:

• no cancer risk for adults can be ascertained, neither in connection with fields from high-voltage lines nor fields in the workplace
• there is no increased incidence of cancer in children who have been exposed to fields weaker than 0.4 µT (microtesla) averaged over time
• the pooling of statistical demographic studies (epidemiological studies) has shown a statistical link between unusually strong magnetic fields (stronger than 0.4 µT on average) and childhood leukaemia
• it has not been possible to find any indication of an increased incidence of other types of cancer in children
• testing on animals and cells did not establish a causal relationship
• theoretical science has been unable to explain how magnetic fields could be the cause of the statistical link with childhood leukaemia, as demonstrated in some studies.

The IARC's five cancer risk categories
Based on the statistical link demonstrated in epidemiological studies the IARC has classified magnetic fields as 'possibly carcinogenic to humans'. This is one of the IARC’s five permanent categories, which are as follows:

In its fact sheet no 322 (2007) WHO states that a well-known substance in this category (2.b) is coffee. Coffee may possibly cause bladder cancer, but at the same time it might protect against colon cancer. Another effect in the same category is welding fumes.

When the IARC assesses whether a specific impact may be the cause of cancer, the organisation follows some very stringent rules where it is the weight of the total scientific documentation that counts. The IARC uses category 2.b when - as is the case with magnetic fields - there is 'limited evidence' from statistical demographic studies and 'inadequate/inconsistent' evidence from experimental research on animals and cells.

This does not mean that it has been proved or it has been deemed possible or probable that children will develop cancer due to magnetic fields. Rather, it means that researchers have come to the conclusion that this could possibly be the case - even if they have been unable to demonstrate a causal link. One type of studies (epidemiology) speaks in favour hereof, but there are still uncertainties. Other types of studies point in the opposite direction as do the attempts to find a theoretical, scientific explanation. There may therefore be other explanations for the statistical results and magnetic fields.