The capacity of a substance to injure a person by chemical means. All substances are toxic; they differ in degree of toxicity and in the nature of injury they may cause. Toxicity is ACUTE when the adverse effect is the result of swallowing a substance, having it on the skin for a few hours, or breathing it for up to a work shift. Toxicity is CHRONIC when the adverse effect is the result of swallowing, contact, or breathing almost daily for a year or longer. SUBACUTE is used for effects of exposure periods between acute and chronic. Toxic effects may be reversible or irreversible. With a reversible effect, soon after exposure ceases, the affected person returns completely to normal. There is no residual effect whatsoever. An Irreversible effect is a permanent change in an affected person. The next exposure is more likely to have a serious effect, because the response starts at a higher baseline
