Hazard vs Risk

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The words ‘hazard’ and ‘risk’ are often confused.  Understanding the difference between ‘a hazard’ and ‘a risk’ is important for understanding the role of toxicology in assessing risks.  A hazard is anything that can cause harm, whereas risk is the potential for a hazard to cause harm.   You can also think of it this way:  A hazard will not pose any risk to you unless you are exposed to enough of that hazard to cause harm.  Risks associated with hazards can be eliminated, or at least greatly reduced, by reducing exposure.

The relationship between risk and hazard can be simplified as:


Understanding the level of exposure to a hazard can help us better to appreciate the risk associated with that hazard.

Here are some examples that illustrate the difference between hazard and risk, the importance of exposure in this relationship, and how you can usually eliminate or at least greatly reduce the risk of harm caused by hazards.


Example 1:

Hazard:  Asbestos is a naturally-occurring, fibrous, heat-resistant mineral material which may be found in some building materials like floor and ceiling tiles.  Asbestos is also found in some natural water supplies.  Both oral exposure through water consumption and inhalation exposure through air containing asbestos are potential routes.   The type of route and potential hazard we address here is through inhalation of asbestos fibers.   It is important to understand first that asbestos is only a inhalation hazard to human health if the asbestos fibers are airborne and near where a person can inhale them–but not if the fibers are still embedded or stuck in the tile or floor of a building.

Human health risks:   Can cause lung diseases such as cancer and also asbestosis, which is not itself fatal although sometimes debilitating and can progress to cancer.

How can the risks be eliminated?   By taking appropriate precautions (respirator, protective clothing) to avoid exposure if working in an environment where airborne asbestos is present (for example during demolition of buildings containing asbestos), or by avoiding getting too close to buildings undergoing demolition.  If asbestos is in materials in a home and is in good shape and is not airborne, it is recommended that it not be disturbed, as that may be the best way to eliminate risks. Alternatively, if repairs are needed, simply sealing the asbestos containing materials can also decrease risks.


Example 2:

Hazard:  The Ebola virus is the agent that causes Ebola virus disease (EVD), formerly known as Ebola haemorrhagic fever, a severe, often fatal illness in humans. The virus is transmitted to people from wild animals and spreads in the human population through human-to-human transmission.

Human health risk:   If a person is infected with the Ebola virus there is a high risk of death.

How can the risk be eliminated?   A person can be infected only by coming in contact with bodily fluids from another person who is infected with the Ebola virus.  For people living in the three West African countries where there has been a major outbreak with tens of thousands of cases recently, the risk of being infected (exposure) is considerably higher than it is for someone living in the United States where less than a handful of cases have been diagnosed.  In those countries with outbreaks, the risk of infection can be reduced or eliminated by avoiding contact with persons showing signs of illness from the virus.


Example 3:

Hazard:  UV radiation from the sun

Human health risks:  Overexposure may lead to sunburn, heat stroke, skin cancer, premature aging, retinal damage, allergic reactions, and immune suppression.

How can those risks be eliminated or at least significantly reduced?   By wearing sunblock and protective clothing and limiting time in direct sunlight.


These are only a few representative examples.  In virtually every situation, whether the hazard is chemical, biological, or physical, you can usually decrease your exposure such that the hazard does not pose any significant risk.


The application of toxicology that focuses on determining the risk related to a particular hazard is known as risk assessment.  The Toxicology Education Foundation’s video “Is It Safe? Evaluating Chemical Risks” is another more in depth resource also recommended for more information on this topic even if one does not necessarily have an extensive technical or scientific background.  The video explains how risks are evaluated.  It is particularly useful for understanding principles and offers tools one can use to better understand the possibility that a substance will cause harm under a given set of circumstances.



Recommended link to start learning more about this topic:

Alternative links:

  • Provided by “Risk Bites”, https://www.youtube.com/watch?v=VF-8QksiU7c (1:30). This video assumes that the audience already understands the difference between possibility and a probability. This concept may need further explanation for certain audiences.


  • Provided by “ACSA Safety”, https://www.youtube.com/watch?v=Gh5Rjs2oOnE (2:23). The focus here is for a general audience and provides a good explanation of probability; however, viewers should keep in mind that this is a safety training video, so one of the messages stressed is precaution or “to err on the side of safety.”  That is not always the only option, or even the best option, when many different factors must be considered.


“Is It Safe?  Evaluating Chemical Risks”   Video by TEF in English, Spanish, and English with Japanese subtitles

An introduction to principles and concepts applied to understanding chemical hazards. “RITE” — risk is dependent upon toxicity and exposure — is among the fundamental concepts discussed.  The video discusses examples from everyday life, such as how one can eliminate risk of lead poisoning while renovating old homes and removing old paints containing lead.   The English version of “Is It Safe?” also available as a two-part series on YouTube

Part 1 (8:30):


Part 2 (7:28):



“Is It Safe? Evaluating Chemical Risks” Primer   A 23-page pamphlet that elaborates upon key concepts and principles introduced by the “Is It Safe?” video.


(revised 8/2/2016 from original posting on 1/28/2015)