Benzene is a volatile aromatic hydrocarbon that is a component of gasoline and is used in many manufacturing processes. Thus, it is present in the general environment, but usually at low levels. The toxic effects of benzene are varied; acute exposure affects the central nervous system, whereas chronic exposure causes damage to the hematopoietic system.
Since benzene is frequently used in industrial processes and is present in gasoline, workers employed in chemical plants and gas stations are most likely to be exposed to it; however, it is also present in the general environment, being released from paints, automobile exhausts, and cigarette smoke. Its concentration is higher indoors than outdoors, especially in homes where there are smokers.
Apart from workplace accidents, acute poisoning can follow unintentional consumption or inhalation of benzene or benzene-containing solutions at home, usually by children; exposure can also occur by intentional use of hydrocarbons, such as recreational abuse, or suicide attempts.
Acute ingestion or inhalation of benzene affects mainly the central nervous system (CNS) and is believed to be mediated by benzene itself, although there are claims  that benzene’s metabolites may also play a role. The signs are similar to alcohol intoxication and are the same irrespective of whether the chemical is inhaled or ingested, except for the irritation of the mucous membranes of the respiratory tract when the route is by inhalation. Also, according to some reports  the lethal dose (LD50) is higher by two orders of magnitude for hydrocarbons entering the body by ingestion than by inhalation. Therefore, aspiration of benzene-containing liquids, including vomitus is a major hazard. Mild exposure results in a headache, dizziness, euphoria, nausea, vomiting, tightness in the chest, and dyspnea. Higher concentrations may cause visual problems, ventricular fibrillation, paralysis, tremor, convulsions, or loss of consciousness . Death can occur after large doses of benzene due to ventricular fibrillation.
In contrast to acute poisoning, the chronic effects of benzene on the cells of the hematopoietic system are mediated by its metabolic products . All of these are oxidized derivatives (phenol, hydroquinone, catechol, benzenetriol, hydroquinone, and trans-Muconic acid). These are reactive chemical species and may contribute to benzene’s effects through different pathways, making the mechanism of toxicity a complex issue . Patients suffering from chronic exposure present with general symptoms. These can include fatigue, weight loss, headaches, dizziness, weakness, pale skin, bleeding gums, nosebleeds, and bruising.
Chronic exposure to benzene may result in dysfunction of the hematopoietic system due to the chemical interfering with renewal and differentiation of stem cells; consequently, both anemic and leukemic diseases may develop .
Patients with chronic exposure may display signs of anemia and poor immunity. Sometimes, the condition of aplastic anemia caused by benzene exposure includes symptoms of hemolysis, such as mild bilirubinemia, shortened erythrocyte life-cycle and similar signs that are not present in idiopathic disease .
Leukemia may follow pancytopenia or aplastic anemia in about a quarter of the leukemia patients , often after a lag of several years . Case reports and epidemiological studies demonstrate a variety of responses to chronic benzene exposure: both acute and chronic leukemias and other disorders are found. For example, among 74,828 people exposed to benzene, 82 were identified with hematopoietic diseases, with cases of acute leukemia, myelodysplastic syndrome, chronic granulocytic leukemia, malignant lymphoma and aplastic anemia . In another study, among 28,460 people working in factories where they were exposed to benzene, 30 cases of leukemia were found, most of which were of the acute type . The International Agency for Research on Cancer has determined that benzene is a carcinogen.
In acute cases, people displaying neurological symptoms of benzene poisoning should be monitored for inadequate oxygenation. Even if only small amounts have been inhaled or ingested, patients should be transferred to a healthcare facility for evaluation. For severely affected patients, toxicologists, and poison centers should be consulted.
Exposure to benzene can be detected by measuring the concentration in blood, exhaled breath, and urine; this – or routine blood work - can also be used to monitor workers in hazardous occupations. There is a linear relationship between benzene levels in the patients’ environment and in their biological samples . However, measuring benzene itself may not be completely reliable when there has been exposure to only a low level. Urinary benzene metabolites (trans-Muconic acid and S-phenyl mercapturic acid) are more suited for the measurements of low exposures , and thus, for monitoring general populations . Albumin adducts of benzene derivatives can be used to measure longer term exposure .
Since benzene is a hematopoietic toxin, detection of hematologic abnormalities by a complete blood count with differential, erythrocyte indices, and thrombocyte counts is the most basic examination. Patient history may reveal current or past occupational or environmental exposure to benzene. Further tests may be needed to exclude other forms of anemia. Examination of bone marrow can produce highly variable results in that patients can have hypoplastic or hyperplastic bone marrow  .