Volcanoes pose a threat to almost half a billion people; today there are approximately 500 active volcanoes on Earth, and every year there are 10 to 40 volcanic eruptions. Volcanic eruptions produce hazardous effects for the environment, climate, and the health of the exposed persons, and are associated with the deterioration of social and economic conditions. Along with magma and steam (H2O), the following gases surface in the environment: carbon dioxide (CO2) and sulphur dioxide (SO2), carbon monoxide (CO), hydrogen sulphide (H2S), carbon sulphide (CS), carbon disulfide (CS2), hydrogen chloride (HCl), hydrogen (H2), methane (CH4), hydrogen fluoride (HF), hydrogen bromide (HBr) and various organic compounds, as well as heavy metals (mercury, lead, gold). Their unfavourable effects depend on the distance from a volcano, on magma viscosity, and on gas concentrations. The hazards closer to the volcano include pyroclastic flows, flows of mud, gases and steam, earthquakes, blasts of air, and tsunamis. Among the hazards in distant areas are the effects of toxic volcanic ashes and problems of the respiratory system, eyes and skin, as well as psychological effects, injuries, transport and communication problems, waste disposal and water supplies issues, collapse of buildings and power outage. Further effects are the deterioration of water quality, fewer periods of rain, crop damages, and the destruction of vegetation. During volcanic eruptions and their immediate aftermath, increased respiratory system morbidity has been observed as well as mortality among those affected by volcanic eruptions. Unfavourable health effects could partly be prevented by timely application of safety measures. Vulkani predstavljaju prijetnju za gotovo pola milijarde ljudi: danas je na Zemlji aktivno oko 500 vulkana, a svake se godine događa 10 do 40 njihovih erupcija. Posljedice erupcija vulkana odražavaju se na okoliš, utječu na klimu te na život i zdravlje ljudi, a vezani su uz pogoršanje socijalnih i gospodarskih uvjeta života. U okoliš s magmom uz vodenu paru (H2O), na površinu dospijevaju plinovi ugljikov dioksid (CO2) i sumporv dioksid (SO2), ugljikov monoksid (CO), vodikov sulfid (H2S), ugljikov sulfid (CS), ugljikov disulfid (CS2), klorovodik (HCl), vodik (H2), metan (CH4), fluorovodik (HF), bromovodik (HBr) i različiti organski spojevi te teški metali (živa, olovo, zlato). Njihovi nepovoljni učinci ovise o udaljenosti od vulkana te o eruptivnim obilježjima, tj. o viskozitetu magme i koncentraciji plinova. Štetnosti bliže vulkanu uključuju piroklastične rijeke, rijeke blata, plinova i vodene pare, potrese, zračne udare i tsunami. U štetnosti u udaljenim područjima ubrajaju se učinci toksičnosti vulkanskog pepela i zdravstveni problemi vezani uz dišni sustav, oči, kožu, zatim psihološke posljedice, ozljede, komunikacijski i transportni problemi, problem odlaganja otpada i opskrbe vodom, rušenje kuća, kao i pad strujnog napona. Dolazi do pogoršanja kvalitete vode i smanjenja kišnih razdoblja, oštećenja poljoprivrednih usjeva, uništavanja vegetacije. Za vrijeme vulkanskih erupcija i neposredno nakon njih povećan je morbiditet, posebno od respiratornih bolesti, a povećan je i mortalitet osoba zahvaćenih vulkanskom erupcijom. Nepovoljni zdravstveni učinci mogu se djelomično prevenirati pravodobnom primjenom zaštitnih mjera.