Causality versus Correlation: Why don’t we just outright say chemicals cause illness?

In the realm of toxic-free and safer consumer products, you might have noticed that when we refer to chemical health risks we tend to use phrases like, “may increase risk of…” or “connected to” rather than simply saying a chemical “causes” an illness.

Why is this? There are two main reasons, which are tightly connected:

1. We don’t want to overstate claims of causality and lose everyone

One problem the non-toxic movement struggles with is keeping people engaged in forward momentum to change things without scaring everyone away with alarmist or extremist sounding claims. To claim that a chemical causes disease without 100% proof or sufficient evidence, we’re embellishing the truth, simplifying the facts, and we risk discrediting everything completely. While there is strong evidence that there are connections between illnesses and toxic chemicals, toxicologists and ecologists working on these issues work hard to present the information truthfully and in keeping with scientific data.

2. We cannot guarantee causality 100% with the majority of chemicals we suspect to be toxic

Why is this? There are a few reasons, but they come down to a lack of clear, concrete data on the isolated and synergisticˆ impacts of chemicals.

Temporal and spatial disparities:

This is a fancy way of saying that time and space put distance between exposure and illness, creating complexities of pinpointing causes. For example, PCBs are found in areas incredibly far away from anywhere they were actually used. Winds and water currents have moved them around the entire globe, and this is true with other chemicals as well. Additionally, exposure to a chemical in the womb may be the cause of developing a cancer later in life. Toxic chemicals move around so unrestricted, it’s hard to keep track of when and where exposure may have happened that resulted in an illness. On a population scale, some of the effects of chronic exposure to toxic chemicals may not be felt for a generation or two. Or different impacts will be felt generations later that might be hard to trace back to the original source. Today, men are facing decreased sperm counts, and many attribute this to generations of exposure to EDCsˆ.

Our entire world is contaminated:

Scientists are finding it difficult to conduct studies properly due to contamination of our environment, often times eliminating the availability for a control. One example of this situation is from the late 1980s, when two scientists were attempting to conduct studies on breast cancer cell growth in the presence of estrogen. They found all of their cell tissues contaminated with a mystery source of estrogen, which was throwing off their tightly controlled cell experiments. Research halted. At a total loss for answers, they even suspected sabotage at one point. Finally, they tracked down the contamination source to the plastic tubes used to store blood. Chemicals from the tubes, which they’d long assumed to be inert, were leaching into the blood and contaminating it with estrogen. On a broader scale, it’s difficult to assess human health impacts from exposure when all of us are polluted to some degree.

There was little testing conducted to begin with:

Thousands of chemicals were introduced to consumer markets without proper testing of each chemical, let alone testing for synergistic impacts. With some chemicals, it’s hard to say which one causes a problem, or if health risks only appear when chemicals are used in certain combinations. We don’t really know because no one bothered to check that carefully.

The impacts of toxic chemicals are often subtle, rather than direct and obvious:

With some toxins, illness caused is simple to identify because it happens quickly and directly. This is the case with extreme exposure to radiation, or acute poisoning from certain heavy metals. Many pesticides used during the 1950s/1960s had clear and often immediate health consequences for humans and the environment. However, many toxic chemicals on the market today change DNA and slowly impair bodily functions, or cause unseen damage to fetuses. Considering how many chemicals we are exposed to, sometimes it can be hard to identify which one might be the culprit.


The current evidence against toxic chemicals remains in the area of correlation. One exception is the case of the DES Daughters. DES (diethylstilbestrol), banned in 1971, was a synthetic estrogen drug given to women during the 1940s and 1950s to prevent miscarriages. The effects of DES were realized after doctors in Boston saw a startling increase in young women with an extremely rare form of vaginal cancer. The mothers of these young women had all taken DES while pregnant. Most of the health impacts of DES were not present at birth, but began to appear as the women reached puberty, childbearing age, and mid-life. DES Daughters are twice as likely to develop breast cancer, and face high rates of other ovarian and vaginal cancers, infertility, and reproductive organ deformities.

Possibly, if we can pinpoint extreme exposure cases or track and correlate specific habits and behaviors with chemical exposure, we may find stronger links between health risks and specific chemicals.


Endocrine Disrupting Compounds and Cancer in Wildlife and Humans (research paper written by me!)
Our Stolen Future by Theo Colborn, Dianne Dumanoski, and John Peterson Myers
Not Just a Pretty Face by Stacy Malkan

ˆ Denotes a term that is defined/explained under the terms/concepts/glossary page of blog. Symbol found following the word the first time it’s used in a post.


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