There have been a few reports in the news recently about how the US government has added formaldehyde to their list of substances known to cause cancer in humans. This doesn’t really come as a surprise – the International Agency for Research on Cancer (IARC), for example, already classifies formaldehyde as a confirmed human carcinogen. But since there’s some media attention on the subject right now, and since formaldehyde exposure can occur from a variety of sources, including many consumer products, it seems a good time to look at what this classification means for the general public.
First, a bit of background. As described in the US National Toxicology Program’s (NTP) 12th Report on Carcinogens, the main evidence supporting this classification is from human occupational studies. Specifically, there have been several studies showing higher rates of nasopharyngeal cancer and sinonasal cancer (basically cancers of the upper part of the throat and nasal cavity, respectively) among industrial workers with high levels of formaldehyde exposure. These cancers are fairly rare in the general population, and the incidence of these cancers has been shown to increase at higher levels of formaldehyde exposure. It has also been shown that formaldehyde can cause damage to DNA in nasal tissues, showing that there is a plausible mechanism by which formaldehyde can cause these cancers. These data alone are pretty much a slam-dunk argument that show formaldehyde can cause cancer in humans, despite claims from the American Chemistry Council that the classification is not warranted.
There is also some evidence of formaldehyde being associated with blood-related cancers such as leukemia, although the evidence is a bit more mixed there. There are also animal studies showing evidence of carcinogenicity from both inhalation and oral (in water) exposures.
Just because a substance is capable of causing cancer doesn’t automatically mean that it will have an effect on the general population, however. The studies showing human carcinogenicity are all involving people with abnormally high exposures, including various industrial workers and embalmers. To determine the likelihood of formaldehyde causing cancer in humans, we need to consider both its potency as a carcinogen and the amount of exposure.
Everyone is exposed to formaldehyde. It is in the air we breathe, the water we drink (whether from a municipal system or bottled water), and the food we eat. It is also produced naturally within the human body as part of our metabolism. Based on data published by the World Health Organization, typical concentrations in outdoor air are on the order of about 10 μg/m3 (micrograms formaldehyde per cubic meter of air), and concentrations in indoor air are on the order of about 30 μg/m3. Concentrations in water can be around 20 μg/litre. Overall, the NTP concluded that typical exposures include about 0.5 to 2.0 mg (milligrams) each day from air, while the exposure from water would probably work out to about 0.03 mg each day. Higher exposures can occur from tobacco smoke, particularly second-hand smoke. Exposures can also occur from various consumer products, including an estimated exposure of 0.1 mg from applying hand creams or suntan lotion. The amount of formaldehyde found in blood in humans from natural metabolic processes is about 2 to 3 μg/g, which would work out to about 150 to 200 mg in an average sized adult.
The World Health Organization looked at the risk of getting cancer from typical formaldehyde exposures. They concluded that the risks of getting cancer from typical exposures are extremely low – less than 2.7 cases in 100,000,000 people (generally anything less than 1 in 1,000,000 is considered to be negligible), based primarily on nasal cancers. This evaluation suggests that normal exposures to formaldehyde are not likely to be a concern for the general population. The total amount of formaldehyde exposure is also generally much less than the amount of formaldehyde naturally present in the body, again suggesting fairly limited risk. The main risks are associated with occupational exposures.
Despite the low risks, many regulatory agencies handle confirmed human carcinogens differently than other chemicals. This means that some form of regulatory action may be required to manage risks from the substance. This is particularly true for chemicals such as formaldehyde that can directly damage DNA. Typically these actions involve the development of a risk management plan to minimize exposures and phase out unnecessary uses (e.g. uses where another, less harmful chemical could be used without significant economic consequences).