Workplace Solutions Chemical safety Workplace exposures

Chemical exposure pathways

How can hazardous chemicals enter the human body? What should safety professionals know about each avenue of entry?

Photo: Milos Dimic/E+ via Getty Images

Responding is Jeffery Buckau, D.O., MSc, CSM, CSP, professor of occupational safety and health, Columbia Southern University, Summerville, SC.

Chemicals, either in a toxic form or used for medicinal purposes, can enter the body through four avenues: absorption, ingestion, inhalation and injection.

In many medical use cases, a common avenue is ingestion.1 Think of the pills, capsules and liquids used to treat different diseases or ailments. Ingestion requires a chemical to be digested through the gastrointestinal tract and, ultimately, into the blood stream, where the chemical is filtered by the liver and then distributed throughout the body to the affected cells that require the medication. This avenue does take some time for the entire process to work properly.

Absorption occurs when a chemical is exposed to the skin. The substance is absorbed either into the cells locally or into the blood stream, where it’s transported throughout the body. A nitroglycerin topical patch, for example, is sometimes used by patients who have angina. Another substance is the topical fentanyl analgesic, which can be up to 100 times more potent than morphine. This substance can be highly misused and dangerous to anyone who encounters it.2

Inhalation is the third route of entry. A substance is taken in through either the nasopharynx (the upper part of the throat behind the nose) or oropharynx (the part of the throat at the back of the mouth behind the oral cavity) and enters the lungs directly. Albuterol breathing treatments used to treat asthma is one example.

Another, more insidious substance is cigarette smoke. The smoke is inhaled into the lungs and its toxic substances are absorbed and enter the blood stream.

Injection is another possible avenue. A common injectable substance is the annual influenza vaccine. In this instance, the injection medium carries small doses of the virus from the intramuscular injection site into the blood stream, where the body recognizes the virus particles as “non-self” and begins to mount an immune response. This response is in the form of memory immune cells that become dormant until the next exposure of the virus, wherein the memory immune cells go into rapid replication to help fight off any new exposure. This same vaccine route is what is used for almost all viral and some bacterial infection prophylactic protection.

For occupational safety and health professionals who may have had an encounter with a dangerous chemical substance, getting answers to the following questions is vital:

  • What route of entry into the body did the worker experience?
  • How much of the chemical were they exposed to?
  • How long were they exposed to the chemical?

Depending on the route of entry of the offending chemical, the time of exposure and dosage can differ dramatically. When discussing this with employees, it’s important to stress the route of entry, the time exposed and the dose.


1. Sweigard, J. (Sept. 21, 2020). How to take oral medications properly. Retrieved from on May 12, 2021.
2. NIDA (Feb. 28, 2019). Fentanyl DrugFacts. Retrieved from on May 12, 2021.

Editor's note: This article represents the independent views of the author and should not be construed as a National Safety Council endorsement.

Post a comment to this article

Safety+Health welcomes comments that promote respectful dialogue. Please stay on topic. Comments that contain personal attacks, profanity or abusive language – or those aggressively promoting products or services – will be removed. We reserve the right to determine which comments violate our comment policy. (Anonymous comments are welcome; merely skip the “name” field in the comment box. An email address is required but will not be included with your comment.)