For example, methanol that has been swallowed may cause blindness. Certain chemicals may affect a target organ. For example, lead primarily affects the brain, kidney and red blood cells and some solvents may harm the liver and kidneys. 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 usually reversible.
Chronic toxicity results from repeated exposure over a long period of time. Effects are usually delayed and gradual, and may be irreversible. For example, the acute effect of drinking alcohol is becoming drunk, while the chronic effect from drinking alcohol over a long period of time is cirrhosis of the liver. Some people may be more or less sensitive the chemicals, depending on several factors including eating habits, physical condition, obesity, medical conditions, drinking and smoking, and pregnancy. Over a period of time, regular exposure to some substances can lead to the development of an allergic rash, breathing difficulty, or other reactions.