Local injuries involve the area of the body in contact with the chemical and are typically caused by reactive or corrosive chemicals, such as strong acids, alkalis or oxidizing agents. Systemic injuries involve tissues or organs unrelated to or removed from the contact site when toxins have been transported through the bloodstream. For example, methanol that has been ingested may cause blindness, while a significant skin exposure to nitrobenzene may effect the central nervous system. Certain chemicals may affect a target organ. It is important to distinguish between acute and chronic exposure and toxicity.
Acute toxicity results from a single, short exposure.
Effects usually appear quickly and are often reversible. Chronic toxicity results from repeated exposure over a long period of time. Effects are usually delayed and gradual, and may be irreversible. Acute and chronic effects are distinguished in the MSDS, usually with more information about acute exposures than chronic. Relatively few chemicals have been evaluated for chronic effects, given the complexity of that type of study.