Cancer myths

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Can the chemicals in sunscreen cause cancer?

We’re often asked if chemicals in sunscreens are harmful, and if they increase your risk of developing cancer. Sunscreen has been used by a large portion of the population for a number of decades and there is no evidence that users come to harm. The research on the chemicals in sunscreen (oxybenzone, retinyl palmitate and parabens) does not show that they cause cancer. None of these chemicals has been classified as a cancer-causing substance by any major scientific organisation. 

A few studies have suggested that parabens (preservatives used in many cosmetic products, including some sunscreens) act like estrogen in the body, which can speed up the growth of breast cancer tumours. We need more research to understand this association better.

Skin cancer is the UK and Ireland’s most common cancer with a well-recognised link between excess sun exposure and skin cancer. Being safe in the sun is still the best way to reduce your risk of developing skin cancer. Protect yourself when the sun is at its strongest, cover your skin with clothing, wear a hat and sunglasses and use a sunscreen with an SPF 30 or higher.

Does fluoride cause cancer?

This is one of our most common queries and with many myths circulating, one that is actually quite easy to provide reassurance on. In short, the fluoride in our tap water (and toothpaste) is not a cause for concern when it comes to cancer.

What is fluoride?

Fluorine is a common element in many things around us. Chemically it belongs to a group of elements which include Chlorine and Iodine. Fluoride is the salt form of the element fluorine. Each of these elements share the characteristic of being highly reactive and liking to bond with other elements, like carbon. In free or acid form, that reactivity makes them very dangerous but when they do bind they make very strong bonds which become extremely unreactive. By way of example, the related element Chlorine is the reactive part of common household bleach and Hydrochloric acid (both very dangerous) but our bodies are also made up of large amounts of Chlorine (Chloride) and we consume it in substances like salt (sodium chloride). So Chlorine is vital to health. Fluorine is a component of lots of substances around is. For example, roughly 1 in 5 of all medicines have Fluorine in them, because Fluoride in such substances can give very useful properties.

Why is fluoride added to water?

Fluoride is very commonly found naturally dissolved in water across the globe. When water filters down through various rocks it tends to dissolve fluoride salts. Hence, water from certain types of wells, aquifers etc (ground water) will sometimes contain proportionately high amounts of dissolved fluoride. Much of the public water supply in Ireland comes from surface run off (rivers, lakes etc) and hence tends to have much lower fluoride levels unless supplemented.

Fluoride was identified as a component of human bones and teeth in the 19th century. In the early part of the 20th century a number of dentists and dental researchers examined tooth decay rates. They found associations between low levels of fluoride and high rates of decay. Conversely, in a region of Colorado, it was common to see staining on teeth. This was found to reflect higher than normal concentrations of fluoride in the teeth (from local drinking water) and these teeth (and especially the stained areas) were very resistant to decay.  There were no other untoward health effects seen when fluoride was found at high levels in public water.  Some fairly crude experiments with supplementing fluoride into public water schemes showed clear and measurable decreases in levels of tooth decay. Hence, many countries with low fluoride levels in their water adopted water fluoridation employing a fluoride-containing salt that is mined from certain rocks. Fluoride has also been supplemented in other materials, eg milk or table salt, but most commonly we see it in toothpaste. Fluoride becomes concentrated in saliva and coats in tiny amounts on to the surface of teeth making them less reactive to acidic by-products of bacteria which can grow in our mouth. Since everyone drinks water, addition of fluoride is a simple, effective and equitable public health measure to reduce tooth decay (and associated diseases) irrespective of financial means. The increased use of toothpaste and regular brushing also accomplishes the same outcome but this tend to benefit more those who are wealthier.

What does the evidence say?

There have been quite a few studies of cancer, examining associations between fluoride and risks of certain cancers. Some references to articles from professional organisations such as the Health Research Board (HRB), Centres for Disease Control (CDC) are listed below. No evidence has been found to support fluoride having any effect on general cancer levels or deaths. As fluoride can be found in bone as well as teeth, cancer of the bone has been a particular research focus.  One laboratory study suggested a possible link. Human studies have suggested extremely small differences both for and against a role for fluoride in bone cancer. This is very common in studies looking at something where there is no difference. In other words, some studies find a tiny positive effect, some find a small negative effect. This is described as “regression toward the mean” and suggests that fluoride has no role in cancer. If there is a role, it is extremely small effect and likely to favour a lower rate of bone cancers in those drinking fluoridated water.


Taking all of this together, Fluoride is added to drinking water as part of measures to reduce tooth decay. There is no evidence that Fluoride in water or toothpaste has any effect on cancer risk.

Further Reading:

Are powerlines, phones, radio masts and communication devices causing cancer?

This is one of the most common queries that we receive in the Irish Cancer Society. We therefore thought we’d spend a little time addressing this frequently asked question.

The quick answer is powerlines and masts do not cause cancer. But read on for a little bit more detail which hopefully explains things a bit better.

Electricity and magnetism

Electricity and magnetism are all around us and always have been. Any flow of electricity generates a changing magnetic field (called an electromagnetic field, EMF) radiating invisibly around that flow. Relatedly (but not exactly identical) communication devices (mobile phones, radios, etc) manipulate high frequency electromagnetic waves (radio frequency radiation) to transmit their signals (sound, data video etc) (more on that next month!!). Don’t let the term 'radiation' frighten you, as the scientific use of radiation simply refers to energy radiating from a source (not specifically the nuclear stuff!) Think of the radiator on your wall radiating heat energy radiation, for example.

These forms of electro-magnetism have always been around us. The earth is magnetic (this is the basis of the magnetic compass) and that electromagnetic field protects us on earth from a variety of harmful particles emitted by the sun which would otherwise be fatal to all life on earth. Radio signals are generated by astronomical bodies and bathe our planet constantly (the basis of radio astronomy). Static electricity and thunderstorms also generate a variety of different types of currents and fields. Obviously there has been a big increase in the types of fields around us as we become more dependent on technology.

Where have fears about cancer risks with power lines come from?

Mains electricity in our homes is usually at 220V. However, to transmit the amounts needed for cities, electricity must be transmitted at much higher voltages, thousands of times higher, through bigger cables. The fields around such cables are likewise somewhat stronger (albeit that strength falls off very dramatically with small differences in distances from the cable). The effects of such fields can be in part visualised with fluorescent tubes placed at ground level immediately under them (see a cool video of this).

Some years ago, researchers looking at geographical patterns of cancer diagnosis found some evidence of a small increase in the rates of rare childhood blood cancers (but not other forms of cancer) among some, but by no means all, communities living close to power lines. The rates of other cancers were unchanged. These findings spurred further interest into whether the EMF might be causing this small increase in childhood leukemias. Similar findings were also seen internationally around some nuclear reprocessing plants but not nuclear power plants.

Initially, lots of different mechanisms were proposed as to how EMF might contribute to this small increase in children’s cancer numbers. Decades of analysis has now shown that these cancers occur where rural populations rapidly mix with more urban or “new” groups of people. In other words, lots of new people come into smaller, isolated communities. This in part explains why the findings were sporadic. Mixing tends to happen around new industrial projects located in rural areas and in specific patterns of the countryside as cities spread.

This population mixing can introduce largely insignificant infections (mostly viruses) into these groups of people. These infections in combination with certain mutations found to occur occasionally in the immune systems of children, can lead to a proportionately temporary (few years) increase in rates of blood cancers among children. Once these infective agents become part of the background of infections for such communities, the rates of childhood blood cancers fall back to the national rate.

So while initially there were some concerns that there could be a small increased risk of more children’s cancers occurring around powerlines, we now know that it’s not due to electricity.

Please see this article in Nature and this article in the British Journal of Cancer for some more background.

Do mobile phones, mobile phone masts, Wi-Fi or 5G cause cancer?

Last month we spoke about whether there were cancer risks from the electromagnetic radiation from power lines.  

Communications devices such as mobile phones rely on a slightly different aspect of electromagnetism associated with radiofrequency electromagnetic waves, so this month we’re going to look at the question as to whether mobile phones; the masts they connect to; Wi-Fi in our homes; and related new technology (such as 5G) might cause cancer.

Some background on communication devices

Radio frequency communications (such as Wi-Fi, mobile phones and new 5G technology) are based on a somewhat different aspect of electro magnetism to that around high voltage power cables. This technology is relatively new so it’s natural to have some concerns about health consequences.

Brain tumours have always occurred and rates of most forms of brain tumour remain largely constant. If one developed a brain cancer and a used mobile phone regularly, it would be rational to wonder if the tumour diagnosis could result from mobile phone use.

Early communication devices relied on proportionately large power outputs by the devices and transmitter masts. This is why early mobile phones similarly required proportionately large batteries to work. Major technological advances have resulted in modern devices operating at small fractions of the energy of earlier models. The drive to increase reliability and the charge interval on such devices combined with desires to reduce any possible safety issues for those in the immediate vicinity of transmission masts has resulted in vastly more efficient communications reliant on much lower energy transmission. We’ve had large scale public mobile phone technology for over 20 years and we know that those older mobile phones and masts which operated at higher powers don’t cause cancers so we can be even more confident that modern versions also pose no cancer risk.

What the research tells us

Mechanistically, on the whole, we know there is no increase in human cancers from communications devices from looking at cancer numbers over time. Experimentally we know of no fundamental biophysical or biochemical mechanism for these signals to interact with important cellular functions (such as DNA or enzymes). However, some animal experiments have given complex findings. Most notable is the US National Toxicology Programme study which exposed rats and mice to massive doses of power from, equivalent to early generation mobile phones, constantly over their whole lives. They found small increases in rates of heart cancer in male rats and possibly some increases in adrenal gland and brain cancers. However, there were no differences in female rats and no differences in male or female mice exposed to the same conditions. (By the way, they also found that the average animal in the mobile phone exposed group lived longer too.) Rats and mice also aren’t humans so it is hard to really extrapolate any findings conclusively to human beings anyway.

The cancer monitoring body of the World Health Organisation, the International Agency for Research on Cancer (IARC), had also looked at the available data and concluded that radio frequency electromagnetic fields were a possible carcinogen. It is important to understand that this category is used for agents for which there is limited evidence of carcinogenicity in either animals or humans, so “possible” in no way means that something does cause cancer, nor does it reflect the magnitude with which something could cause cancer. As already mentioned, there is some research in support of that but when taken as a whole, this categorisation and the rest of the available data indicates that there is simply no evidence to support worrying about phones, masts etc when talking about cancer risk. In addition, the changes to frequency used by technology such as 5G means that these signals cannot even penetrate the human body.


So bringing this and last month’s articles together, while there are lots of other issues we might worry about with new technology, cancer isn’t one of them. Cables and masts can be an eyesore, our overuse of phone technology can contribute to other societal issues but when it comes to cancer we might better focus our efforts on the real challenges in our community - the things we can do which are proven to reduce our cancer risk and the efforts we must all make to ensure everyone in our community gets the best chance of a good outcome during and after treatment.

If you'd like to learn more about reducing your cancer risk, The European Code Against Cancer was developed by the International Agency for Research on Cancer and the European Commission. Cancer specialists and scientists from across Europe compiled the code based on the latest scientific evidence on cancer prevention.

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