The mono-, di-, and trinitrobenzenes are absorbed chiefly through the skin and through inhalation of the dust or vapor when these materials are heated. The dinitrobenzenes are believed to be somewhat more toxic than the mononitrobenzenes and more toxic than aniline. The effect of di- and trinitrobenzene on the body is similar to that of aniline and mononitrobenzene, with reduction of the oxygen-carrying power of the blood and depression of the nervous system being responsible for most of the symptoms following acute exposure. Poisoning with the solid nitro compounds is usually slower and less severe than is the case with the liquid nitro and amino benzenes since absorption is less rapid. Thus, chronic poisoning occurs more frequently than acute, the picture observed in the chronic form being one of anemia, moderate cyanosis, fatigue, slight dizziness, headache, insomnia, and loss of weight. Prolonged chronic exposure may result in damage to the liver and kidneys, with production of acute yellow atrophy, toxic hepatitis, and fatty degeneration of the kidneys. The introduction of one or more Cl atoms into the nitrobenzene ring results in the formation of chloronitrobenzene compounds or nitrochlors. The chloro-mono-nitrobenzenes have essentially the same toxic effect as nitrobenzene. The Cl derivatives of dinitrobenzene, on the other hand, while resembling dinitrobenzene in their systemic effects, are much more irritating to the skin. They act as direct irritants and, in addition, may cause sensitization.

Dangerous; many of these compounds are highly flammable and some are explosive, especially those with more than one nitro group on the ring (polynitroaryls, such as trinitrobenzene, trinitrotoluene, tetranitro-N-methylaniline, trinitrophenol). The presence of alkali increases the thermal sensitivity of the explosive materials. Industrial explosions have occurred in this manner. When heated to decomposition they evolve highly toxic fumes of NO_x. See specific nitro compounds.