Researchers use 2 main types of studies to try to determine if a substance or exposure causes cancer. (A substance that causes cancer or helps cancer grow is called a carcinogen.) In studies done in the lab, animals are exposed to a substance (often in very large doses) to see if it causes tumors or other health problems. Its not always clear if the results from these types of studies will apply to humans, but lab studies are the best way to detect the potential for a substance to cause cancer in humans before widespread exposure occurs. Another type of study looks at cancer rates in different groups of people. Such a study might compare the cancer rate in a group exposed to a substance versus the rate in a group not exposed to it, or compare it to what the expected cancer rate would be in the general population. But studies in people can sometimes be hard to interpret, because there may be other factors affecting the results that are hard to account for. In most cases neither type of study provides definitive evidence on its own, so researchers usually look at both human and lab-based studies. Studying something like hair dyes can be even more complicated because they may contain any of thousands of different chemicals. On top of this, the ingredients in hair dyes have changed over the years. Early hair dyes contained chemicals, including some aromatic amines, which were found in the late 1970s to cause cancer in lab animals, so hair dye manufacturers changed some of the chemicals in their products. Studying exposure to hair dyes from decades ago may not be the same as studying current exposures. In fact, many studies classify personal hair dye use based on whether it took place before or after 1980.
Posted on: Wed, 13 Nov 2013 18:13:12 +0000
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