Breathing very high levels of benzene can result in death. High levels of benzene exposure can cause drowsiness, dizziness, rapid heart rate, headaches, tremors, confusion, and unconsciousness. Eating or drinking foods containing high levels of benzene can cause vomiting, irritation of the stomach, dizziness, sleepiness, convulsions, rapid heart rate, and death.

The major effect of benzene from long-term exposure is on the blood. Benzene causes harmful effects on the bone marrow and can cause a decrease in red blood cells leading to anemia. It can also cause excessive bleeding and can affect the immune system, increasing the chance for infection.

Long-term exposure to high levels of benzene in the air and especially dermal contact can cause leukemia, particularly acute myelogenous leukemia, often referred to as AML. This is a bllod cancer of the blood-forming organs in particular in the bone marrow where blood cells originate. The Department of Health and Human Services (DHHS) has determined that benzene is a known human carcinogen. The International Agency for Research on Cancer (IARC) and the EPA have determined that benzene is carcinogenic to humans.