What are carcinogens and why are they dangerous?

You probably have been advised to avoid carcinogenic material in daily life, but have you ever wondered what it is and why it can be so dangerous? The definition of a carcinogen is a substance which can cause cancer (the “uncontrolled division of abnormal cells in a part of the body”) in living tissue. Carcinogens come in groups, defined as the following by the International Agency for Research on Cancer (IARC):

Group 1: Carcinogenic to humans Group 2A: Probably carcinogenic to humans Group 2B: Possibly carcinogenic to humans Group 3: Not classifiable as to its carcinogenicity to humans

Common carcinogens include tobacco, ultraviolet radiation and alcohol, all of which are Group 1 carcinogens. What makes these unsafe is the chemicals that they contain or release when used.

At least 70 chemicals found in tobacco are confirmed to be carcinogenic, 3 of which are formaldehyde, arsenic and benzene. Formaldehyde is a colourless gas with a strong smell. It is frequently found in pressed-wood products, glues, the coatings of paper products and, tobacco. It has been deemed carcinogenic because studies have shown that workers who have been exposed to formaldehyde have a higher risk of myeloid leukaemia (the cancer of the white blood cells). Another study has shown that these workers had abnormal levels of mutations in their chromosomes of early white blood cells in their bone marrow. This suggests that there is likely a link between exposure to formaldehyde and developing leukaemia. Based on this evidence, the National Toxicology Program (NTP), a section of the United States' Department of Health and Human Services, listed formaldehyde as a known human carcinogen. Benzene exposure is also similar – it has been proven to be linked to the cancers of blood cells. The IARC has deemed arsenic to be a carcinogen, able to cause lung, bladder and skin cancer. Inorganic arsenic compounds have proved they cause cancer by affecting DNA repair mechanisms, and chromosomal anomalies are seen in those exposed to arsenic. The smoking of tobacco causes 15% of the UK’s cancer cases.

UV radiation contains three main groups: UVA rays, UVB rays, and UVC rays, in order from lowest to highest energy. UVA rays have the least energy, meaning they can indirectly damage the DNA in cells and are usually responsible for ageing skin cells. The damage they cause is over long-term in most cases; however, it is suggested that they contribute to certain skin cancers. UVB rays have more energy than UVA rays, and they damage DNA more directly – this makes them cause the majority of skin cancers, in addition to being responsible for

sunburn. UVC rays have the most energy, but they react with the ozone layer and do not come into contact with humans. As they originate from the sun, they are not as notable a risk as UVB rays for skin cancer. The damage that UV radiation does to DNA can get repaired by the body. However, repeated exposure does not allow the cells’ DNA to repair fully, which can trigger genetic mutations, leading to skin cells to multiplying quickly, causing cancerous tumours.

Regular intake of alcoholic beverages can also cause cancer because when ethanol has been consumed, the liver converts it into a chemical called acetaldehyde. Sometimes a little bit of the ethanol can break down in the mouth and stomach into acetaldehyde too. If there is an excess of alcohol consumed, the body will not be able to process it fast enough, so acetaldehyde builds up in the body. Acetaldehyde is a toxic chemical which can lead to DNA damage which is irreversible. This can cause cancers of the bowel, mouth, oesophagus and throat. Excessive alcohol intake can also cause breast cancer; it can lead to a rise in oestrogen levels, which can in turn affect the development of breast tissue, increase the production of cells and damage DNA. Furthermore, if alcohol remains in the mouth, it can act as a solvent for other carcinogens to absorb into the cells, namely chemicals in tobacco from smoking. Heavy alcohol consumption is the cause of 3.3% of cancer cases in the UK.

It is difficult to find all the carcinogenic substances that exist,and prove they can cause cancer as tests and research do not always give definite answers. There are many possible carcinogens you may not have expected – one being a chemical in French fries. When some types of foods with a high starch content – e.g. potatoes – are fried, a natural chemical reaction can occur to form acrylamide. Acrylamide is a Group 2A carcinogen. Some studies have shown that rats who drank water containing acrylamide developed cancer, so researchers have concluded that human bodies may act in the same way. Another can be found in microwave popcorn: the actual popcorn, you may be relieved to hear, is safe, although the lining of the microwaveable bag contains perfluorooctanoic acid (a Group 2B carcinogenic acid). Lab studies have exposed animals to perfluorooctanoic acid to monitor any signs of tumours and found there was an increased risk of developing malignant tumours in certain areas. Although, not enough research has been done to confirm that these are carcinogens – do not worry just yet!

So, in summary, carcinogens are substances which can cause cancer by damaging the DNA of cells. There are many types of carcinogens, which have been classified in groups of their suspected carcinogenicity. Further research is required to prove whether something can cause cancer or not. This can be achieved using epidemiology studies as well as lab studies of animals. However, it remains there are still many more carcinogens to be discovered. By Kat 9M