What does it mean to be healthy?
Health means feeling well in body, mind and social life. A person with no illness but who is lonely or always anxious is not fully healthy.
A disease is any condition that stops part of the body or mind working properly. Its symptoms are what the person feels (pain, tiredness); its signs are what others can see or measure (fever, rash, high blood pressure).
Signs that you may be ill
- fever (body temperature above about 37.5 °C), chills;
- cough, sore throat, runny nose;
- vomiting, loose motions, stomach pain;
- rash, swelling, unusual tiredness, losing weight without trying.
Mental health matters as much as physical health: talk to a trusted adult if sadness, worry or stress lasts for weeks.
Communicable diseases and how they spread
Pathogens are tiny living things (or viruses) that cause disease:
- Bacteria – e.g. tuberculosis, cholera, typhoid;
- Viruses – e.g. flu, common cold, measles, COVID-19;
- Fungi – e.g. ringworm, athlete's foot;
- Protists – e.g. malaria (carried by mosquitoes).
Ways of spreading
- Air: droplets from coughs and sneezes.
- Water and food: dirty water, unwashed hands.
- Direct contact: touch, body fluids, shared towels.
- Vectors: mosquitoes, flies, ticks.
- Animals (zoonoses): rabies from dog bites, Lyme disease from ticks, bird flu.
To remove a tick, grip it close to the skin with fine tweezers, pull straight out slowly, clean the skin and watch for a spreading red ring or fever in the next weeks.
Non-communicable and chronic diseases
Non-communicable diseases (NCDs) cannot be caught from someone. Many are chronic – they last a long time. Examples:
- Heart disease and stroke – fatty plaque narrows arteries; a blocked artery in the heart causes a heart attack, in the brain a stroke.
- High blood pressure (hypertension) – often no symptoms, but strains the heart and blood vessels.
- Type 2 diabetes – blood sugar stays too high.
- Many cancers – cells divide out of control.
- Allergies and asthma – the immune system over-reacts to harmless things like pollen or dust.
Risk factors: smoking, alcohol, unhealthy diet, too little exercise, obesity, air pollution, too little sleep, plus genes and age. People living with a chronic illness or recovering from a stroke may need medicines, therapy and patience from those around them.
Staying healthy and preventing disease
- Hygiene: wash hands with soap for 20 seconds, cover coughs, keep food covered and cooked well.
- Sanitation: clean drinking water, toilets and safe waste disposal stop many water-borne diseases.
- Vaccines: a harmless form of the pathogen trains the immune system to make antibodies in advance. When most people are vaccinated, the germ cannot find new people to infect: herd immunity.
- Food: a balanced diet with fruit and vegetables, less sugar, salt and fried food.
- Exercise: about 60 minutes of activity a day for teenagers.
- Sleep: 8–10 hours for teenagers.
- Teeth: brush twice a day with fluoride toothpaste, limit sugary snacks and drinks, visit a dentist.
Healthy weight: BMI and waist
BMI = mass (kg) ÷ height² (m²). For adults, 18.5–24.9 is the healthy range; 25–29.9 is overweight; 30 or more is obese. For children, BMI is compared with charts for age and sex. A large waist (fat around the belly) is a strong warning sign of metabolic syndrome: high blood pressure, high blood sugar and high blood fats together.
Antibiotics, safe medicines and resistance
Antibiotics kill bacteria or stop them growing. They do nothing against viruses, so they will not cure a cold or flu.
Antibiotic resistance: in any group of bacteria a few may, by chance, survive the drug. If treatment stops early or antibiotics are used when not needed, these survivors multiply and the drug no longer works.
Using medicines safely
- Read the leaflet: what it is for, dose, how often, side effects, who must not take it, expiry date.
- Take antibiotics exactly as prescribed – the right dose, at the right times, for the full number of days.
- Never share prescription medicines or use leftover ones.
- Avoid needless over-the-counter pills and supplements; more is not better and some harm the liver or kidneys.
Recreational drugs
Alcohol, tobacco and illegal drugs change how the brain and body work: slower reactions, poor judgement, addiction, damage to the liver, lungs and heart.
Check-ups, screening, donation and first aid
Screening and self-checks
Screening tests healthy-looking people to find disease early, when treatment works best. Many countries run free national programmes, for example blood pressure checks, cholesterol tests, and screening for breast, cervical and bowel cancer at set ages.
- Blood pressure is written as two numbers, e.g. 120/80 mmHg. Repeated readings of 140/90 or more mean high blood pressure.
- Skin and moles: see a doctor if a mole changes shape, colour or size, bleeds or itches (ABCDE: asymmetry, border, colour, diameter, evolving).
- Breast or testicle self-exam once a month: report any new lump or change.
Donating blood, marrow and organs
Healthy adults can donate blood (usually from age 18) and join stem-cell (marrow) registers. Organs can be donated after death, and some, like a kidney, by living donors. Countries use either an opt-in system (you register consent) or an opt-out system (you are a donor unless you record an objection). Always tell your family your wish.
Technology and health
Medical technology – scans, vaccines, insulin pumps, transplants, apps that track activity – saves lives, but screens and poor posture can also harm health.
First aid and safety
Check the scene is safe, call for help (112 in India and Europe), keep the person still and warm, press on bleeding, cool burns under running water for 20 minutes.
Try it: your health check
Measure your height (m) and mass (kg) and work out BMI = mass ÷ height². Count your fruit and vegetable portions and active minutes today. Put the numbers into the free-play sliders and see your risk meter. Which one change would lower it most?
Key formulas and definitions
- BMI = mass (kg) ÷ height² (m²)
- Adult BMI: below 18.5 underweight · 18.5–24.9 healthy · 25–29.9 overweight · 30+ obese
- Normal blood pressure about 120/80 mmHg; high if often ≥ 140/90
- Communicable = caused by a pathogen, can spread; non-communicable = cannot spread
- Antibiotics → bacteria only, never viruses
Worked examples
1. A person has mass 72 kg and height 1.8 m. Find the BMI and say which range it is in.
BMI = 72 ÷ 1.8² = 72 ÷ 3.24 ≈ 22.2. This is in the healthy range (18.5–24.9).
2. Sort into communicable and non-communicable: malaria, diabetes, tuberculosis, asthma, measles, stroke.
Communicable: malaria, tuberculosis, measles. Non-communicable: diabetes, asthma, stroke.
3. A student has a cold and asks for leftover antibiotics. What would you tell them?
A cold is caused by a virus, so antibiotics will not help. Taking them without need also helps resistant bacteria to spread. Rest, fluids and seeing a doctor if it gets worse is better, and never use leftover medicines.
4. In a town of 1 000 people, 900 are vaccinated against measles. Explain why the 100 unvaccinated are partly protected.
Measles needs to pass from person to person. With 90% vaccinated, most people around an infected person cannot catch it, so the chain breaks quickly. This is herd immunity. (Measles is very infectious, so about 95% is needed for full protection.)
Common mistakes
- Thinking health only means not being ill. Mental and social well-being are part of health too.
- Using antibiotics for colds and flu. They work only on bacteria, not on viruses.
- Stopping antibiotics as soon as you feel better. This leaves the toughest bacteria alive and causes resistance.
- Believing non-communicable diseases only affect old people. Habits formed as a teenager raise or lower the risk for life.