Health and disease
Beyond NCERT In the NEET syllabus; the Class 12 book has no section for it.
Quick answer
Health is a state of complete physical, mental and social well-being, not simply the absence of disease; NCERT says it is affected by genetic disorders, infections and life style. Infectious diseases are easily transmitted from one person to another, while among non-infectious diseases cancer is the major cause of death.
What is health?
Health
- Health does not simply mean the absence of disease or physical fitness (page 130).
It could be defined as a state of complete physical, mental and social well-being.
NCERT Biology (Class 12), Chapter 7, Introduction, page 130
In plain words: being healthy is more than not being ill. Physical, mental and social well-being all matter. This broad ideal is not a diagnostic test or a judgement of someone’s worth, personality or productivity.
The 2026–27 NCERT book has no numbered section on health and disease: it covers them on the opening pages of Chapter 7 (pages 129–130). The NEET (UG) 2026 syllabus lists Health and Disease at the start of Unit 8. This page follows those NCERT pages; modern clarifications are distinguished from textbook statements.
From humours to the modern view
- For a long time, health was considered a state of body and mind with a balance of certain ‘humors’. Early Greeks such as Hippocrates, and the Indian Ayurveda system of medicine, asserted this. NCERT associates black bile with heat and fever, but classical Greek humoral accounts usually associate black bile with cold/dry qualities and melancholy; these historical ideas are not modern biological explanations. The idea was arrived at by pure reflective thought (page 129).
- William Harvey’s discovery of blood circulation by the experimental method, and a thermometer showing normal body temperature in persons with blackbile, helped replace speculative accounts with experimental physiology; the textbook compresses a much longer historical change (page 129).
- Later, biology stated that the mind influences the immune system through the neural system and the endocrine system, and that the immune system maintains our health. So the mind and mental state can affect our health (page 129).
- Beyond the NCERT text: the Constitution of the World Health Organization, adopted on 22 July 1946 and in force since 7 April 1948, describes health in the same three parts, physical, mental and social, and adds that being free of illness or weakness is not enough (WHO, “Constitution”, facts in our words).
What affects health
Health is affected by (page 129):
- genetic disorders: deficiencies with which a child is born, and deficiencies or defects that the child inherits from the parents; see genetic disorders in Chapter 4;
- infections;
- life style: the food and water we take, the rest and exercise we give our bodies, and the habits we have or lack (page 129).
Why health matters, and how to keep it (page 130):
- Healthy people are more efficient at work, which increases productivity and brings economic prosperity. Health also increases longevity and reduces infant and maternal mortality.
- A balanced diet, personal hygiene and regular exercise are very important to maintain good health; yoga has been practised since time immemorial for physical and mental health.
- Also necessary: awareness of diseases and their effects on the body, vaccination (immunisation) against infectious diseases, proper disposal of wastes, control of vectors, and hygiene in food and water resources.
Disease: infectious and non-infectious
- When the functioning of one or more organs or systems of the body is adversely affected, with various signs and symptoms, we are not healthy: we have a disease (page 130).
- Diseases can be broadly grouped into infectious and non-infectious (page 130).
- Infectious diseases are easily transmitted from one person to another. They are very common, and every one of us suffers from them at some time. Some, like AIDS, are fatal (page 130).
- Among non-infectious diseases, cancer is the major cause of death. Drug and alcohol abuse also affect our health adversely (page 130).
| Infectious (from the rest of the chapter) | Non-infectious (from the rest of the chapter) |
|---|---|
| typhoid, pneumonia, common cold, malaria, amoebiasis, ascariasis, filariasis, ringworm, dengue, chikungunya, AIDS | cancer; allergies; autoimmune diseases such as rheumatoid arthritis; harm from drug and alcohol abuse |
(Grouped from NCERT Sections 7.1 to 7.5, pages 130–147; our table.)
Solved examples
Example 1: Is a fit person always healthy?
A sprinter is in top physical shape but has been anxious and withdrawn for months. Is the sprinter healthy in NCERT’s sense?
Answer: physical fitness alone does not establish well-being in every domain. Persistent anxiety or withdrawal may warrant support, but this description alone is not enough to diagnose a mental disorder (NCERT page 130).
Example 2: How the humours idea fell
Which examples does NCERT use to illustrate the shift towards experimental explanations of health?
Answer: experiments rather than reflective thought: William Harvey’s discovery of blood circulation by the experimental method, and the thermometer, which showed a normal body temperature in persons with blackbile (NCERT page 129).
Example 3: Sorting diseases
Sort into infectious and non-infectious: malaria, cancer, common cold, rheumatoid arthritis.
Answer: infectious: malaria and the common cold, which pass from person to person (by mosquitoes and by droplets); non-infectious: cancer and rheumatoid arthritis (NCERT pages 130–131, 137 and 140).
Common mistakes to avoid
Common mistake
Defining health as the absence of disease
NCERT says health does not simply mean the absence of disease or physical fitness; it is complete physical, mental and social well-being (NCERT page 130).
Common mistake
Calling cancer infectious
Cancer is a non-infectious disease; among non-infectious diseases, NCERT calls it the major cause of death (NCERT page 130). Beyond the NCERT text: WHO reports that cardiovascular diseases cause the most noncommunicable-disease deaths (WHO, Noncommunicable diseases fact sheet, facts in our words).
Quick revision summary
- Historical humoral accounts were replaced by evidence-based physiology and medicine; NCERT’s story is a simplified history, not a modern explanation of health.
- The mind affects the immune system through the neural and endocrine systems, and the immune system maintains health.
- Health: a state of complete physical, mental and social well-being. Affected by genetic disorders, infections and life style.
- Good health: balanced diet, personal hygiene, regular exercise, yoga, awareness, vaccination, waste disposal, vector control, clean food and water.
- Disease: organs or systems adversely affected, with signs and symptoms. Infectious diseases spread easily (AIDS can be fatal); among non-infectious ones, cancer is the major cause of death.
Formula sheet
- health: complete physical, mental and social well-being
- affects health: genetic disorders, infections, life style
- infectious: easily transmitted from one person to another
- non-infectious: cancer, the major cause of death
Questions students ask
What is the difference between health and disease?
Health is a positive state of the whole person, while a disease is a disturbance in how the body works: NCERT defines health as “a state of complete physical, mental and social well-being” and says we have a disease “when the functioning of one or more organs or systems of the body is adversely affected, characterised by appearance of various signs and symptoms” (page 130). Beyond the NCERT text, MeSH (US National Library of Medicine) also defines a disease by its “characteristic set of signs and symptoms” and adds that “it may affect the whole body or any of its parts”.
Is an infection the same as a disease?
An infection is not the same as a disease: an infection is a pathogen entering the body and multiplying, while a disease is the damage that may follow, with signs and symptoms. NCERT says pathogens “enter our body by various means, multiply and interfere with normal vital activities, resulting in morphological and functional damage” (page 130), and of AIDS it notes: “There is always a time-lag between the infection and appearance of AIDS symptoms” (page 139). Beyond the NCERT text, MeSH (US National Library of Medicine) defines infections as “invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases”.
Are infectious diseases and communicable diseases the same?
Beyond the NCERT text, infectious diseases and communicable diseases are generally used as two names for the same group: MeSH (US National Library of Medicine), the vocabulary that indexes medical research, lists “Infectious Diseases” as an entry term under Communicable Diseases, and “Non-infectious Diseases” under Noncommunicable Diseases. NCERT uses only the pair infectious and non-infectious (page 130).
What causes non-infectious diseases?
Non-infectious diseases do not pass between people; their causes lie in genes, harmful agents, a misdirected immune system or habits (our grouping). NCERT’s Chapter 7 names genetic disorders (page 129); carcinogens, agents that can transform normal cells into cancer cells (page 141); an immune system that over-reacts to allergens or attacks self-cells, in allergies and auto-immune diseases (page 137); and drug and alcohol abuse (page 130). Beyond the NCERT text, MeSH (US National Library of Medicine) gives cardiovascular diseases, cancer, chronic respiratory diseases and diabetes as the four main types of noncommunicable diseases.
What are the main types of infectious diseases?
Infectious diseases can be grouped by the kind of pathogen that causes them, and NCERT lists bacteria, viruses, fungi, protozoans and helminths among the organisms that cause disease in humans (page 130). Its Chapter 7 gives examples of each: typhoid (caused by a bacterium), AIDS (by a virus, HIV), ringworm (by fungi), amoebiasis (by a protozoan) and ascariasis (by the roundworm Ascaris, a helminth) (pages 130–138). The common diseases page pairs each disease with its pathogen and the way it spreads.
Practice questions
Try each question first, then open the answer to check your working.
-
Q1. Name the three things that NCERT says affect health.
Show answerHide answer
Genetic disorders, infections and life style (NCERT page 129).
-
Q2. Through which two systems does the mind influence the immune system?
Show answerHide answer
The neural system and the endocrine system (NCERT page 129).
-
Q3. What does NCERT call an infectious disease? Name one that NCERT calls fatal.
Show answerHide answer
A disease that is easily transmitted from one person to another; such diseases are very common, and some, like AIDS, are fatal (NCERT page 130). Beyond the NCERT text: MedlinePlus says antiretroviral therapy “can make HIV infection a manageable chronic condition” (MedlinePlus, HIV; public domain).