Adolescence is the phase of life between childhood and adulthood, from ages 10 to 19. It is a unique stage of human development and an important time for laying the foundations of good health. Adolescents experience rapid physical, cognitive and psychosocial growth. This affects how they feel, think, make decisions, and interact with the world around them.

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.

Air pollution is contamination of the indoor or outdoor environment by any chemical, physical or biological agent that modifies the natural characteristics of the atmosphere. Household combustion devices, motor vehicles, industrial facilities and forest fires are common sources of air pollution. Pollutants of major public health concern include particulate matter, carbon monoxide, ozone, nitrogen dioxide and sulfur dioxide. Outdoor and indoor air pollution cause respiratory and other diseases, which can be fatal.

Antimicrobial resistance (AMR) happens when microorganisms (such as bacteria, fungi, viruses, and parasites) change when they are exposed to antimicrobial drugs (such as antibiotics, antifungals, antivirals, antimalarials, and anthelmintics). Microorganisms that develop AMR are sometimes referred to as “superbugs”. As a result, the medicines become ineffective and infections persist in the body, increasing the risk of spread to others. AMR occurs naturally over time, usually through genetic changes. However, the misuse and overuse of antimicrobials is accelerating this process.

Blood safety encompasses actions aimed at ensuring that everyone has access to blood and blood products that are as safe as possible, available at reasonable cost, adequate to meet the needs of patients, transfused only when necessary, and provided as part of a sustainable blood programme within the existing health care system.

Cardiovascular diseases (CVDs) are disorders of the heart and blood vessels and include coronary heart disease, cerebrovascular disease, rheumatic heart disease and other conditions. Four out of five CVD deaths are due to heart attacks and strokes. Individuals at risk of CVD may demonstrate raised blood pressure, glucose, and lipids as well as overweight and obesity. These can all be easily measured in primary care facilities. Identifying those at highest risk of CVDs and ensuring they receive appropriate treatment can prevent premature deaths. Access to essential NCD medicines and basic health technologies in all primary health care facilities is essential to ensure that those in need receive treatment and counselling.

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 eating or drinking food or water that is contaminated with the bacterium Vibrio cholerae. Cholera remains a global threat to public health and is an indicator of inequity and lack of social development. Researchers have estimated that every year, there are 1.3 to 4.0 million cases of cholera, and 21 000 to 143 000 deaths worldwide due to the infection.

The resulting changes in the global climate bring a range of risks to health, from deaths in extreme high temperatures to changing patterns of infectious diseases. Climate and weather variables pose threats to food and water security, and cause outbreaks of waterborne and vectorborne diseases. Moreover, the increased pressure on scarce resources triggers climate-related migration and conflicts. Under business-as-usual scenarios, it is estimated that between 2030 to 2050, climate change will cause an additional 250 000 deaths annually.

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.

Diabetes is a chronic, metabolic disease characterized by elevated levels of blood glucose (or blood sugar), which leads over time to serious damage to the heart, blood vessels, eyes, kidneys, and nerves. The most common is type 2 diabetes, usually in adults, which occurs when the body becomes resistant to insulin or doesn't make enough insulin. In the past three decades the prevalence of type 2 diabetes has risen dramatically in countries of all income levels. Type 1 diabetes, once known as juvenile diabetes or insulin-dependent diabetes, is a chronic condition in which the pancreas produces little or no insulin by itself. For people living with diabetes, access to affordable treatment, including insulin, is critical to their survival. There is a globally agreed target to halt the rise in diabetes and obesity by 2025.

Diagnostic imaging is the use of X-ray, ultrasound, radioactive isotopes, or magnetic resonance to produce a visual display or representation of structural and / or functional information of the "inside" of the human body. Diagnostic imaging, especially X-ray based examinations and ultrasonography, is crucial in every medical setting and at all levels of heath care. Though clinical judgment maybe sufficient in treating many conditions, the use of diagnostic imaging services is paramount in confirming, correctly assessing and documenting disease processes and also in judging the disease response to treatment.

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.

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.

Family planning allows individuals and couples to anticipate and attain their desired number of children and the spacing and timing of their births. It is achieved through use of contraceptive methods and the treatment of involuntary infertility. A woman’s ability to space and limit her pregnancies has a direct impact on her health and well-being as well as on the outcome of each pregnancy.

Access to sufficient amounts of safe and nutritious food is key to sustaining life and promoting good health. Unsafe food containing harmful bacteria, viruses, parasites or chemical substances can cause more than 200 different diseases – ranging from diarrhoea to cancers. Around the world, an estimated 600 million – almost 1 in 10 people – fall ill after eating contaminated food each year, resulting in 420 000 deaths and the loss of 33 million healthy life years (DALYs).

Hand hygiene as part of an infection prevention and control programme in all settings that support surgery, prevents patient infection and reduces an avoidable burden on health systems.

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.

Hepatitis is an inflammation of the liver, most commonly caused by a viral infection. There are five main hepatitis viruses, referred to as types A, B, C, D and E. These five types are of greatest concern because of the burden of illness and death they cause and the potential for outbreaks and epidemic spread. In particular, types B and C lead to chronic disease in hundreds of millions of people and, together, are the most common cause of liver cirrhosis and cancer. Hepatitis A and E are typically caused by ingestion of contaminated food or water. Hepatitis B, C and D usually occur as a result of parenteral contact with infected body fluids. Common modes of transmission for these viruses include receipt of contaminated blood or blood products, invasive medical procedures using contaminated equipment and for hepatitis B transmission from mother to baby at birth, from family member to child, and also by sexual contact. Acute infection may occur with limited or no symptoms, or may include symptoms such as jaundice (yellowing of the skin and eyes), dark urine, extreme fatigue, nausea, vomiting and abdominal pain.

Human immunodeficiency virus (HIV) is an infection that attacks the body’s immune system, specifically the white blood cells called CD4 cells. HIV destroys these CD4 cells, weakening a person’s immunity against infections such as tuberculosis and some cancers.

Hospitals play an important role in the health care system. These institutions are crucial in delivering medical, nursing and related services round the clock, assisting the Region to work towards Universal Health Coverage and providing person-centred, equitable and accessible health services of a high standard.

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.

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.

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.

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.

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.

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.

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.

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.

Tropical diseases encompass all diseases that occur solely, or principally, in the tropics. In practice, the term is often taken to refer to infectious diseases that thrive in hot, humid conditions, such as malaria, leishmaniasis, schistosomiasis, onchocerciasis, lymphatic filariasis, Chagas disease, African trypanosomiasis, and dengue.

Noncommunicable diseases (NCDs), including heart disease, stroke, cancer, diabetes and chronic lung disease, are collectively responsible for almost 70% of all deaths worldwide. Almost three quarters of all NCD deaths, and 82% of the 16 million people who died prematurely, or before reaching 70 years of age, occur in low- and middle-income countries. The rise of NCDs has been driven by primarily four major risk factors: tobacco use, physical inactivity, the harmful use of alcohol and unhealthy diets.

WHO recognizes the vital role of nurses and midwives in keeping the world healthy. Comprising more than two-thirds of the health workforce in the South East Asia Region, nurses are critical in responding to health needs in all settings and across the lifespan. In the 2020 International Year of the Nurse and the Midwife, the celebration of the World Health Day is an opportunity to highlight the work of nursing and midwifery around the world while celebrating this workforce as one of the most valuable resources of every country

Nutrition is a critical part of health and development. Better nutrition is related to improved infant, child and maternal health, stronger immune systems, safer pregnancy and childbirth, lower risk of non-communicable diseases (such as diabetes and cardiovascular disease), and longevity.

Occupational health deals with all aspects of health and safety in the workplace and has a strong focus on primary prevention of hazards. The health of the workers has several determinants, including risk factors at the workplace leading to cancers, accidents, musculoskeletal diseases, respiratory diseases, hearing loss, circulatory diseases, stress related disorders and communicable diseases and others. Employment and working conditions in the formal or informal economy embrace other important determinants, including, working hours, salary, workplace policies concerning maternity leave, health promotion and protection provisions, etc.

The global landscape of health care is changing with health systems operating in increasingly complex environments. While new treatments, technologies and care models can have therapeutic potential, they can also pose new threats to safe care. Patient safety is a fundamental principle of health care and is now being recognized as a large and growing global public health challenge. Global efforts to reduce the burden of patient harm have not achieved substantial change over the past 15 years, despite pioneering work in some health care settings. Patient safety is the absence of preventable harm to a patient during the process of health care, including the reduction of risk of unnecessary harm associated with health care to an acceptable minimum. An acceptable minimum refers to the collective notions of given current knowledge, resources available and the context in which care is delivered, weighed against the risk of non-treatment or other treatment.

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

Primary health care enables health systems to support a person’s health needs – from health promotion to disease prevention, treatment, rehabilitation, palliative care and more. This strategy also ensures that health care is delivered in a way that is centred on people’s needs and respects their preferences.

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.

Rabies is a vaccine-preventable zoonotic viral disease that occurs in more than 150 countries and areas. Dogs are the source of the vast majority of human rabies deaths. Infection causes tens of thousands of deaths every year, mostly in Asia and Africa. Once symptoms of the disease develop, rabies is nearly always fatal. However, immediate wound cleansing and immunization within a few hours after contact with a suspect rabid animal can prevent the onset of rabies and death.

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.

Over 3 700 people die on the world's roads every day and tens of millions of people are injured or disabled every year. Children, pedestrians, cyclists and older people are among the most vulnerable of road users. WHO works with partners - governmental and nongovernmental - around the world to raise the profile of the preventability of road traffic injuries and promote good practice related to addressing key behaviour risk factors – speed, drink-driving, the use of motorcycle helmets, seat-belts and child restraints.

Nicotine contained in tobacco is highly addictive and tobacco use is a major risk factor for cardiovascular and respiratory diseases, over 20 different types or subtypes of cancer, and many other debilitating health conditions. Every year, more than 8 million people die from tobacco use. Most tobacco-related deaths occur in low- and middle-income countries, which are often targets of intensive tobacco industry interference and marketing.