Hazard vs Risk

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Many people find it confusing when toxicologists and others talk about hazard versus risk.  To many, they seem to mean the same thing.  They don’t, and assuming they do can lead people to unnecessarily fear ingredients and other chemicals.  This tox topic is intended to help you understand the differences between hazard and risk and why knowing the difference is important to your health and your effort to keep yourself and your family safe from harmful exposures.

Let’s start with definitions.

Hazard:  A potential source of danger/harm.  A hazard evaluation in toxicology focuses on defining what types of harmful effects could occur and under what circumstances (e.g. ingestion, inhalation, skin exposure).  For example, when you read that something can cause damage to your liver, that’s a hazard. It does NOT mean that any exposure, no matter how small, will cause damage.

A toxicologist would create a hazard profile for a chemical by identifying all the ways it could potentially cause harm and the amount of exposure (the dose) necessary to do so.

Risk: The likelihood that harm from a specific hazard will occur.

Toxicologists use the following mathematical analogy to talk about risk:

Risk = Hazard x Exposure

Risk Assessment is the formal process of quantifying risk based on known hazards and the amount of exposure.  Returning to the example of something that can cause liver damage (the hazard), the risk of damaging your liver boils down to whether you are exposed to enough to cause that damage.  A good example of this is the pain reliever acetaminophen.  If you look at the warnings on the bottle you will note that it clearly states that if you take too much you can damage your liver.  But, if you follow the label instructions you can use it safely.  This is why toxicologists say “the dose makes the poison”.

Risk assessments are typically done for specific types of exposure scenarios (e.g. how a chemical is used and how you may actually be exposed via air, water, food, etc.).  For a more in-depth discussion of human health risk assessment, please check out our Tox Topic on this subject (http://toxedfoundation.org/human-health-risk-assessment/).

The bottom line is that even if something is highly hazardous, if you are never exposed to it, or not exposed to enough of it to cause harm, you have little to no risk of having an adverse effect on your health. We can’t change the hazard(s) of a chemical, but we can reduce or eliminate risk by reducing exposure to harmful levels.

Here’s another example to demonstrate how hazard and risk are used together to help prevent harm from chemical exposures.

Asbestos—a naturally occurring fibrous material that can damage the lungs. Asbestos was mined and used commercially in the building and construction industry, shipbuilding industry, and the automotive industry. Health Hazards: Cancer (mesothelioma) and a lung disease called asbestosis.  The primary source of exposure is from breathing airborne particles.  Asbestos fibers embedded in old building materials are only a risk if they are released into the air and you breathe them in.

Ways to reduce or eliminate risk from asbestos.  If you have an older home and suspect it may contain materials with asbestos, have it tested by a qualified expert.  If you need to do home repair and are unsure, wear a respirator and disposable protective clothing.  Use a sealant on any old household building materials that may contain asbestos but which do not currently need repair (asbestos-containing building materials were banned from sale many years ago).

For additional information on safe levels of exposure to asbestos please visit:

https://www.atsdr.cdc.gov/ToxProfiles/tp61.pdf

https://www.epa.gov/sites/production/files/2016-10/documents/asbestos.pdf

For additional perspective on hazard and risk, check out:

Is it Safe?  Evaluating Chemical Risks. TEF’s award-winning video is also available with Spanish, Japanese and Korean subtitling.

Hazard vs Risk Same Difference?  A Risk Bites video by founder and Director of the Arizona State University Risk Innovation Lab, Dr. Andrew Maynard

Revised 8/27/2019