commonly transmitted from pregnant women to their fetuses, and about a third of the infected children will eventually become deaf. Ototoxic and neurotoxic drugs and chemicals Some over-the-counter as well as prescription drugs and certain industrial chemicals are ototoxic. Exposure to these can result in temporary or permanent hearing loss. Some medications cause irreversible damage to the ear, and are limited in their use for this reason. The most important group is the aminoglycosides (main member gentamicin). A rare mitochondrial mutation, m.1555A>G, can increase an individual's susceptibility to the ototoxic effect of aminoglycosides. Long term hydrocodone (Vicodin) abuse is known to cause rapidly progressing sensorineural hearing loss, usually without vestibular symptoms. Methotrexate, a chemotherapy agent, is also known to cause hearing loss. In most cases hearing loss does not recover when the drug is stopped. Paradoxically, methotrexate is also used in the treatment of autoimmune-induced inflammatory hearing loss. Various other medications may reversibly degrade hearing. This includes loop diuretics, sildenafil (Viagra), high or sustained dosing of NSAIDs (aspirin, ibuprofen, naproxen, and various prescription drugs: celecoxib, etc.), quinine, and macrolide antibiotics (erythromycin, etc.). Cytotoxic agents such as carboplatinum, used to treat malignancies can give rise to a dose dependent SNHL, as can drugs such as desferrioxamine, used for haematological disorders such as thalassaemia; patients prescribed these drugs need to have hearing monitored. Prolonged or repeated environmental or work-related exposure to ototoxic chemicals can also result in sensorineural hearing loss. Some of these chemicals are: butyl nitrite – chemical used recreationally known as 'poppers' carbon disulfide – a solvent used as a building block in many organic reactions styrene, an industrial chemical precursor of polystyrene, a plastic carbon monoxide, a poisonous gas resulting from incomplete combustion heavy metals: tin, lead, manganese, mercury hexane, an industrial solvent and one of the significant constituents of gasoline ethylbenzene, an industrial solvent used in the production of styrene toluene and xylene, highly poisonous petrochemical solvents. Toluene is a component of high-octane gasoline; xylene is used in the production of polyester fibers and resins. trichloroethylene, an industrial degreasing solvent Organophosphate pesticides Head trauma There can be damage either to the ear itself or to the central auditory pathways that process the information conveyed by the ears. People who sustain head injury are susceptible to hearing loss or tinnitus, either temporary or permanent. Contact sports like football (U.S. NFL), hockey and cricket have a notable incidence of head