Every person – in every country in the world – should have the opportunity to live a long and healthy life. Yet, the environments in which we live can favour health or be harmful to it. Environments are highly influential on our behaviour and our exposure to health risks (for example air pollution, violence), our access to services (for example, health and social care) and the opportunities that ageing brings.

Antimicrobial resistance (AMR) threatens the effective prevention and treatment of an ever-increasing range of infections caused by bacteria, parasites, viruses and fungi. AMR occurs when bacteria, viruses, fungi and parasites change over time and no longer respond to medicines making infections harder to treat and increasing the risk of disease spread, severe illness and death. As a result, the medicines become ineffective and infections persist in the body, increasing the risk of spread to others. Antimicrobials - including antibiotics, antivirals, antifungals and antiparasitics - are medicines used to prevent and treat infections in humans, animals and plants. Microorganisms that develop antimicrobial resistance are sometimes referred to as “superbugs”.

Cancer is the uncontrolled growth and spread of cells. It can affect almost any part of the body. The growths often invade surrounding tissue and can metastasize to distant sites. Many cancers can be prevented by avoiding exposure to common risk factors, such as tobacco smoke. In addition, a significant proportion of cancers can be cured, by surgery, radiotherapy or chemotherapy, especially if they are detected early.

Protecting and improving the health of children is of fundamental importance. Over the past several decades, we have seen dramatic progress in improving the health and reducing the mortality rate of young children. Among other encouraging statistics, the number of children dying before the age of 5 was halved from 2000 to 2017, and more mothers and children are surviving today than ever before. However, a great deal of work remains to further improve the health outcomes for children. The world is facing a double mandate. More than half of child deaths are due to conditions that could be easily prevented or treated given access to health care and improvements to their quality of life. At the same time, children must also be given a stable environment in which to thrive, including good health and nutrition, protection from threats and access to opportunities to learn and grow. Investing in children is one of the most important things a society can do to build a better future.

Cholera is an acute diarrhoeal infection caused by ingestion of food or water contaminated with the bacterium Vibrio cholerae. Cholera remains a global threat to public health and an indicator of inequity and lack of social development. Researchers have estimated that every year, there are 1.3 to 4.0 million cases, and 21 000 to 143 000 deaths worldwide due to cholera. Cholera is an extremely virulent disease that can cause severe acute watery diarrhoea with severe dehydration. It takes between 12 hours and 5 days for a person to show symptoms after ingesting contaminated food or water. Cholera affects both children and adults and can kill within hours if untreated. Most people infected with Vibrio cholerae do not develop any symptoms, although the bacteria are present in their faeces for 1-10 days after infection and are shed back into the environment, potentially infecting other people. Cholera is often predictable, preventable and can ultimately be eliminated where access to clean water and sanitation facilities, and satisfactory hygiene conditions are ensured and sustained for the whole population.

Climate change is impacting human lives and health in a variety of ways. It threatens the essential ingredients of good health - clean air, safe drinking water, nutritious food supply, and safe shelter - and has the potential to undermine decades of progress in global health. Between 2030 and 2050, climate change is expected to cause approximately 250 000 additional deaths per year, from malnutrition, malaria, diarrhoea and heat stress alone. The direct damage costs to health is estimated to be between USD 2-4 billion per year by 2030.

Coronavirus disease (COVID-19) is an infectious disease caused by a newly discovered coronavirus. Most people infected with the COVID-19 virus will experience mild to moderate respiratory illness and recover without requiring special treatment. Older people, and those with underlying medical problems like cardiovascular disease, diabetes, chronic respiratory disease, and cancer are more likely to develop serious illness.

Rehabilitation of people with disabilities is a process aimed at enabling them to reach and maintain their optimal physical, sensory, intellectual, psychological and social functional levels. Rehabilitation provides disabled people with the tools they need to attain independence and self-determination.

A serious disruption of the functioning of a community or a society causing widespread human, material, economic or environmental losses which exceed the ability of the affected community or society to cope using its own resources.

Course of study required to educate a legally qualified and licensed practitioner of medicine, concerned with maintaining or restoring human health through the study, diagnosis and treatment of disease and injury, through the science of medicine and the applied practice of that science. Gaining a basic medical degree may take from five to eight or even nine years, depending on jurisdiction and university. Medical doctors include generalists and specialists. Medical training completed by internship qualifies a medical doctor to become a physician or a surgeon.

An integrated global alert and response system for epidemics and other public health emergencies based on strong national public health systems and capacity and an effective international system for coordinated response.

Access to appropriate medications is shown to have substantial impacts on community health and the related economic indicators. Quality-assured, safe and effective medicines, vaccines and medical devices are fundamental to a functioning health system. However, globalized trade can undermine regulation, and in resource-limited settings especially, incidence of substandard or falsified medicines is growing. Working to increase access to essential pharmaceuticals while limiting the spread of falsified products is at the heart of WHO’s global strategy on medicines.

Environmental health addresses all the physical, chemical, and biological factors external to a person, and all the related factors impacting behaviours. It encompasses the assessment and control of those environmental factors that can potentially affect health. It is targeted towards preventing disease and creating health-supportive environments. This definition excludes behaviour not related to environment, as well as behaviour related to the social and cultural environment, and genetics.

Statistics refers to both quantitative data, and the classification of such data in accordance with probability theory and the application to them of methods such as hypothesis testing. Health statistics include both empirical data and estimates related to health, such as mortality, morbidity, risk factors, health service coverage, and health systems. The production and dissemination of health statistics is a core WHO activity mandated to WHO by its Member States in its Constitution. WHO programmes compile and disseminate a broad range of statistics that play a key role in advocacy for health issues, monitoring and evaluation of health programmes and provision of technical assistance to countries.

The first International Conference on Health Promotion was held in Ottawa in 1986, and was primarily a response to growing expectations for a new public health movement around the world. It launched a series of actions among international organizations, national governments and local communities to achieve the goal of "Health For All" by the year 2000 and beyond. The basic strategies for health promotion identified in the Ottawa Charter were: advocate (to boost the factors which encourage health), enable (allowing all people to achieve health equity) and mediate (through collaboration across all sectors). Since then, the WHO Global Health Promotion Conferences have established and developed the global principles and action areas for health promotion. Most recently, the 9th global conference (Shanghai 2016), titled ‘Promoting health in the Sustainable Development Goals: Health for all and all for health’, highlighted the critical links between promoting health and the 2030 Agenda for Sustainable Development. Whilst calling for bold political interventions to accelerate country action on the SDGs, the Shanghai Declaration provides a framework through which governments can utilize the transformational potential of health promotion.

Laboratory networks are essential to support disease surveillance and outbreak investigation. Formalized networks facilitate the exchange of knowledge and expertise, thus facilitating timely and appropriate support to surveillance and epidemiology. Laboratory biosafety procedures and practices describe ways to appropriately handle and work with pathogens, minimizing the risk of exposure and infection.

Health systems can only function with health workers; improving health service coverage and realizing the right to the enjoyment of the highest attainable standard of health is dependent on their availability, accessibility, acceptability and quality. WHO estimates a projected shortfall of 18 million health workers by 2030, mostly in low- and lower-middle income countries. However, countries at all levels of socioeconomic development face, to varying degrees, difficulties in the education, employment, deployment, retention, and performance of their workforce.

Hospitals play an important role in the health care system. They are health care institutions that have an organized medical and other professional staff, and inpatient facilities, and deliver medical, nursing and related services 24 hours per day, 7 days per week. Hospitals offer a varying range of acute, convalescent and terminal care using diagnostic and curative services in response to acute and chronic conditions arising from diseases as well as injuries and genetic anomalies. In doing so they generate essential information for research, education and management. Traditionally oriented on individual care, hospitals are increasingly forging closer links with other parts of the health sector and communities in an effort to optimize the use of resources for the promotion and protection of individual and collective health status.

Immunization is a global health and development success story, saving millions of lives every year. Vaccines reduce risks of getting a disease by working with your body’s natural defences to build protection. When you get a vaccine, your immune system responds. We now have vaccines to prevent more than 20 life-threatening diseases, helping people of all ages live longer, healthier lives. Immunization currently prevents 2-3 million deaths every year from diseases like diphtheria, tetanus, pertussis, influenza and measles. Immunization is a key component of primary health care and an indisputable human right. It’s also one of the best health investments money can buy. Vaccines are also critical to the prevention and control of infectious-disease outbreaks. They underpin global health security and will be a vital tool in the battle against antimicrobial resistance.

Equity is the absence of avoidable or remediable differences among groups of people, whether those groups are defined socially, economically, demographically or geographically. Health inequities involve more than inequality with respect to health determinants, access to the resources needed to be healthy or health outcomes. They also entail a failure to avoid or overcome inequalities that infringe on fairness. Reducing health inequities is important because health is a fundamental human right. However, evidence suggests that the impressive health gains achieved over recent decades are unequally distributed and have largely failed to reach the poor and other marginalized or socially excluded groups. Persistent and growing inequalities in health are increasingly evident, both between and within countries.

Seasonal influenza is an acute respiratory infection caused by influenza viruses which circulate in all parts of the world. It represents a year-round disease burden. It causes illnesses that range in severity and sometimes lead to hospitalization and death. Most people recover from fever and other symptoms within a week without requiring medical attention. However, influenza can cause severe illness or death, particularly among high risk groups including the very young, the elderly, pregnant women, health workers and those with serious medical conditions. In temperate climates, seasonal epidemics occur mainly during winter, while in tropical regions, influenza may occur throughout the year, causing outbreaks more irregularly.

Malaria is caused by parasites that are transmitted to people through the bites of infected female mosquitoes. P. falciparum is the most deadly malaria parasite and the most prevalent in Africa, where malaria cases and deaths are heavily concentrated. The first symptoms of malaria – fever, headache, chills and vomiting – usually appear between 10 and 15 days after the mosquito bite. Without prompt treatment, P. falciparum malaria can progress to severe illness and death. WHO recommends a multi-pronged strategy to prevent, control and eliminate malaria. Key interventions include: the use of insecticide-treated mosquito nets and indoor residual spraying, diagnostic testing, and treatment of confirmed cases with effective anti-malarial medicines. In recent years, these measures have dramatically lowered the malaria burden in many settings. Malaria transmission continues in many countries around the world however, and causes hundreds of thousands of deaths each year.

Maternal health refers to the health of women during pregnancy, childbirth and the postnatal period. Each stage should be a positive experience, ensuring women and their babies reach their full potential for health and well-being.

Measles is a highly contagious viral disease whose common complications include pneumonia and diarrhoea. Death may occur in up to 5-10% of infected young children in developing countries. Rubella is also a contagious viral disease, but milder than measles. However, when rubella infects a pregnant woman during the first half of her pregnancy, there is danger of fetal death or birth defects affecting primarily the eyes, ears, heart, and brain.

Mental health refers to a broad array of activities directly or indirectly related to the mental well-being component included in the WHO's definition of health: "A state of complete physical, mental and social well-being, and not merely the absence of disease". It is related to the promotion of well-being, the prevention of mental disorders, and the treatment and rehabilitation of people affected by mental disorders. The harmful use of alcohol is a global problem which compromises both individual and social development. It results in 3.3 million deaths each year. Alcohol is the world's third largest risk factor for premature mortality, disability and loss of health; it is the leading risk factor in the Western Pacific and the Americas and the second largest in Europe. Alcohol is associated with many serious social and developmental issues, including violence, child neglect and abuse, and absenteeism in the workplace. It also causes harm far beyond the physical and psychological health of the drinker. It harms the well-being and health of people around the drinker. An intoxicated person can harm others or put them at risk of traffic accidents or violent behaviour, or negatively affect co-workers, relatives, friends or strangers. Thus, the impact of the harmful use of alcohol reaches deep into society.

WHO and its many partners regularly deploy mobile clinics and medical teams to reach people cut off from access to health services. For many people, these mobile clinics and teams may be their only source of health care. Mobile clinics offer flexible and viable options for treating isolated and vulnerable groups as well as to newly displaced populations. When coordinating crisis response, WHO arranges for mobile health care teams to go by foot, bike, moto, boat or vehicle. The demand for mobile units keeps rising. WHO may buy mobile clinics or supply them, or pay for partners to buy or supply them.

Regular physical activity is proven to help prevent and manage noncommunicable diseases (NCDs) such as heart disease, stroke, diabetes and several cancers. It also helps prevent hypertension, maintain healthy body weight and can improve mental health, quality of life and well-being. Physical activity refers to all movement. Popular ways to be active include walking, cycling, wheeling, sports, active recreation and play, and can be done at any level of skill and for enjoyment by everybody.

Poliomyelitis (polio) is a highly infectious viral disease that largely affects children under 5 years of age. The virus is transmitted by person-to-person spread mainly through the faecal-oral route or, less frequently, by a common vehicle (e.g. contaminated water or food) and multiplies in the intestine, from where it can invade the nervous system and cause paralysis.

More people are on the move now than ever before. There are an estimated 1 billion migrants in the world today of whom 258 million are international migrants and 763 million internal migrants – one in seven of the world’s population. 68 million of the world’s internal and international migrants are forcibly displaced today. This rapid increase of population movement has important public health implications, and therefore requires an adequate response from the health sector.

TB is caused by bacteria (Mycobacterium tuberculosis) and it most often affects the lungs. TB is spread through the air when people with lung TB cough, sneeze or spit. A person needs to inhale only a few germs to become infected. Every year, 10 million people fall ill with tuberculosis (TB). Despite being a preventable and curable disease, 1.5 million people die from TB each year – making it the world’s top infectious killer. TB is the leading cause of death of people with HIV and also a major contributor to antimicrobial resistance.

Universal health coverage means that all people have access to the health services they need, when and where they need them, without financial hardship. It includes the full range of essential health services, from health promotion to prevention, treatment, rehabilitation, and palliative care. Currently, at least half of the people in the world do not receive the health services they need. About 100 million people are pushed into extreme poverty each year because of out-of-pocket spending on health. This must change.

Yellow fever is an epidemic-prone mosquito-borne vaccine preventable disease that is transmitted to humans by the bites of infected mosquitoes. Yellow fever is caused by an arbovirus (a virus transmitted by vectors such mosquitoes, ticks or other arthropods) transmitted to humans by the bites of infected Aedes and Haemagogus mosquitoes. These day-biting mosquitoes breed around houses (domestic), in forests or jungles (wild), or in both habitats (semi-domestic). Yellow fever is a high-impact high-threat disease, with risk of international spread, which represents a potential threat to global health security. There are 3 types of transmission cycles. The first is sylvatic (or jungle) yellow fever in which monkeys, which are the primary reservoir of yellow fever, are bitten by wild mosquitoes that pass the virus on to other monkeys and occasionally humans. The second is intermediate yellow fever in which semi-domestic mosquitoes infect both monkeys and people. This is the most common type of outbreak in Africa. The third is urban yellow fever of which large epidemics occur when infected people introduce the virus into heavily populated areas with high mosquito density and where people have little immunity. In these conditions, infected mosquitoes transmit the virus from person to person.

Safe drinking-water, sanitation and hygiene are crucial to human health and well-being. Safe WASH is not only a prerequisite to health, but contributes to livelihoods, school attendance and dignity and helps to create resilient communities living in healthy environments.