Class 8 Science · Chapter 3 NotesHealth: The Ultimate Treasure

Health is more than just the absence of disease. According to the World Health Organization (WHO), health is a state of complete physical, mental, and social well-being. This means a healthy person feels good physically, stays positive mentally, and has strong relationships socially. Our lifestyle and environment greatly influence our health. Good habits like eating a balanced diet, exercising regularly, getting enough sleep, and managing stress contribute to overall well-being. The chapter also introduces Ayurveda, which emphasizes balance between body, mind, and surroundings through daily routines (dinacharya) and seasonal routines (ritucharya).

• WHO definitionHealth is a state of complete physical, mental, and social well-being, not merely the absence of disease.
• Physical healthBody functions properly, we feel energetic.
• Mental healthPositive mindset, ability to cope with stress.
• Social healthGood relationships with family, friends, and community.

A disease is a condition that affects the normal functioning of the body or mind. Diseases can be broadly classified into two types: communicable and non-communicable. Communicable diseases are caused by pathogens like bacteria, viruses, fungi, worms, or protozoa, and they spread from one person to another. Non-communicable diseases are not caused by pathogens and do not spread; they are often linked to lifestyle, diet, and environment. Examples of communicable diseases include typhoid, dengue, flu, chickenpox, and COVID-19. Non-communicable diseases include cancer, diabetes, and asthma. In India, non-communicable diseases are becoming more common due to changes in lifestyle.

• PathogensDisease-causing organisms such as bacteria, viruses, fungi, worms, protozoa.
• Communicable diseasesSpread from person to person.
• Non-communicable diseasesDo not spread; linked to lifestyle, diet, environment.
• Deficiency diseasesCaused by lack of specific nutrients (e.g., scurvy, anaemia, goitre) and are non-communicable.

Communicable diseases spread through various routes: air (coughing, sneezing), direct contact (shaking hands), indirect contact (sharing personal items), contaminated food and water, and vectors (insects like mosquitoes and houseflies). Common examples include common cold, influenza, chickenpox, measles, tuberculosis, hepatitis A, cholera, typhoid, ascariasis, malaria, and dengue. Prevention involves maintaining personal hygiene, washing hands frequently, covering mouth and nose while coughing or sneezing, wearing masks in crowded places, avoiding sharing personal items, keeping food and water clean, and controlling mosquito breeding. Vaccination also plays a crucial role in preventing many communicable diseases.

• VectorsInsects like mosquitoes and houseflies that transmit pathogens.
• Preventive measuresHandwashing, covering mouth and nose, using masks, safe food and water, mosquito nets.
• VaccinesTrain the immune system to fight specific diseases.

Non-communicable diseases (NCDs) are not caused by pathogens and do not spread from person to person. They are often chronic, lasting more than three months, and are linked to lifestyle, diet, and environment. Common NCDs include diabetes, heart disease, cancer, asthma, and obesity. In India, NCDs are the leading cause of death. Risk factors include unhealthy eating habits, lack of physical activity, being overweight, and tobacco use. Prevention focuses on healthy lifestyle choices: balanced diet, regular exercise, avoiding tobacco and alcohol, and managing stress. Early diagnosis and continuous care are important for managing NCDs.

• Chronic diseasesLast for a long time (more than 3 months).
• DiabetesCaused by hormonal imbalances, unhealthy diet, inactivity, obesity.
• ObesityExcess body weight; managed by balanced diet and exercise.
• High blood pressureOften linked to lifestyle; managed with diet and exercise.

Personal hygiene includes practices like bathing regularly, washing hands with soap, brushing teeth, and wearing clean clothes. These habits help prevent infections and keep us healthy. Public health involves community-level efforts to prevent disease and promote health, such as safe drinking water, proper sanitation, waste disposal, and vaccination campaigns. The chapter gives an example from Odisha where a community-led sanitation campaign reduced open defecation and improved child health. A clean environment—clean air, water, and surroundings—is essential for good health. Air pollution from vehicles and factories can cause respiratory problems, and the Air Quality Index (AQI) helps monitor air quality.

• Personal hygieneHandwashing, bathing, oral care, clean clothes.
• Public healthSanitation, safe water, waste management, vaccination drives.
• AQIAir Quality Index indicates how clean or polluted the air is.

A balanced diet provides all the nutrients our body needs in the right proportions. It includes carbohydrates, proteins, fats, vitamins, minerals, and water. Eating plenty of fruits, vegetables, and whole grains is important. We should avoid processed, fatty, and sugary foods and drinks. Deficiency of specific nutrients can lead to deficiency diseases like scurvy (vitamin C), anaemia (iron), and goitre (iodine). The chapter emphasizes reducing oil and sugar intake and avoiding junk food. A healthy diet, combined with regular exercise and adequate sleep, helps maintain a healthy weight and prevents non-communicable diseases like obesity and diabetes.

• Balanced dietIncludes all nutrients in correct proportions.
• Deficiency diseasesScurvy, anaemia, goitre.
• Healthy eatingFruits, vegetables, whole grains; limit processed and sugary foods.

Immunity is the body's natural ability to fight diseases, provided by the immune system. Vaccines help prevent serious infections by training the immune system to recognize and attack harmful germs, providing acquired immunity. Vaccines can be made from weakened or dead pathogens, or harmless parts of pathogens. Edward Jenner discovered the first vaccine (smallpox) using cowpox. India has a traditional practice called variolation. Vaccines are preventive, not curative. Treatment of diseases includes antibiotics for bacterial infections, but antibiotics do not work against viruses. Misuse of antibiotics leads to antibiotic resistance, where bacteria survive and multiply despite treatment. Traditional medicine systems like Ayurveda, Siddha, and Unani focus on natural remedies and lifestyle.

• ImmunityBody's ability to fight diseases.
• VaccinesProvide acquired immunity; preventive, not curative.
• AntibioticsKill bacteria; ineffective against viruses; misuse leads to resistance.
• Antibiotic resistanceBacteria become resistant due to indiscriminate use.