Definitions of Health Hazards and Risks: Toxicology, Chemical and Biological Hazards, and Phases of Epidemiological Transition

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Risks and Hazards

A risk is the possibility of suffering harm from a hazard that can cause injury, disease, economic loss or any type of environmental damage. Risk is always measured in terms of probability, with 0 being no risk at all and 1 being absolute certainty that the risk will occur. There are four major types of hazards: cultural, chemical, physical and biological. Cultural risks include poor diet, drug use, poor driving and assault. Chemical risks include harmful chemicals in the air, water, soil and consumed food. Physical risks are fire, weather and radiation. Biological risks include pathogens, allergens and possible diseases spread from animals.


Toxicology is the study of the potential harmful effects of chemicals on health. The measure of the degree of harm that a substance can cause is called toxicity. The most preventable cause of death is tobacco which kills over 400,000 people in the United States alone. Obesity is also a large problem in developed countries, with its prominent effects most evident in the UNited States.

In the United States, cigarettes are the only consumed products that are not required to list ingredients. However, they may contain over 500 different ingredients such as urea, which is a component of urine, cyanide which is found in rat poison, and methanol which is a prominent component of rocket fuel.

Chemical and Biological Hazards

Hazardous chemicals are known to be flammable or explosive, irritating or damaging to the lungs and can also interfere with oxygen intake and cause allergic reactions. Mutagens in chemicals can cause DNA mutations, and carcinogens can promote growth of dangerous tumors.

Biological hazards are categorized into nontransmissible and transmissible. Nontransmissible diseases include diabetes and malnutrition and cannot be passed from one person to another and are not caused by living organisms. Transmissible disease include HIV, tuberculous and Ebola and can be spread from one person to another and are caused by living organism. The pathogen is the infectious agent that causes transmissible diseases.

Epidemiological Transition

As a country becomes more industrialized, a epidemiological transition will occur in the types of diseases that affect the general population. As a country has more money, there becomes less emphasis on fighting infectious diseases, but rather on chronic diseases because the population is living longer. There are five phases to the epidemiological transition that a country will go through.

  • Phase one occurs when a country faces high death rates due to epidemics and famines.
  • Phase two is characterized by less frequent epidemic peaks and a slightly lower death rate due to slight medical advances.
  • As the death rate levels off, phase three occurs where most deaths are caused by transmissible diseases that are caused by aging.
  • Phase four continues with a level death rate and an increased life span due to increased medical advances.
  • Phase five has not yet occurred anywhere but is proposed and is marked by an increase in death due to the reemergence of new infectious diseases that are caused by urbanization and resistance by bacteria to antibiotics.