In the workplace, we often interact with the same chemicals on a regular basis or we use chemicals only once for maintenance or a non-routine task. This is why we study the short-term and long-term affects of chemicals on the body. Long-term or chronic exposure is repeated contact with the same chemical day after day over many years. This can lead to poisoning and damage certain organs. Chronic toxicity often occurs after many years of exposure. The other type of chemical interaction in the workplace is a one-time exposure known as short-term or acute exposure. If the chemical is highly toxic even a one-time exposure can overwhelm the body. The understanding of acute toxicity comes from studies with animals exposed to relatively high doses of the chemical. Accidental chemical exposure, spills and emergencies also cause acute toxicity in humans. The health effects may be temporary, such as skin irritation, dizziness or nausea, or they may be permanent: blindness, scars from acid burns, mental impairment and so on.