• Written By Taufiya Tazeen
  • Last Modified 02-11-2022

Human Health and Diseases: Types, and Immune System


We all are aware of the pandemic situation that the whole world is facing today. We are fighting the situation by awareness to handle the spread and proper preventive measures. This proves that to live a healthy life, we need to understand the concept of human health and diseases that tend to deviate from the state of being healthy.

The disease-causing microorganism is described as a pathogen. Furthermore, there are several ways through which these pathogens or bacterias can enter the human body. These pathogens enter the human body transmitting various types of diseases. In this article, we will learn what we mean by health, diseases and immunity. Scroll down to learn more!

What is Health?

Health does not only mean “absence of diseases” or “absence of physical fitness”; it is much more than that. According to the World Health Organization (WHO), health is defined as the state of complete physical, mental and social well being and not merely the absence of disease or infirmity. Good or balanced health is a state of optimum physical fitness, alertness, mental maturity, freedom from anxiety and social tensions.

Three Aspects of Health

Fig: Three Aspects of Health

Health is affected by factors such as:
1. Genetic disorders, deficiencies born with or inherited from parents.
2. Infections
3. Lifestyle, including food, water, rest, exercise, habits, etc.
Good health is maintained through a balanced diet, personal hygiene and regular exercise.

What is Disease?

What is COVID-19? You might already know, it is an infectious disease caused by a virus named coronavirus. So, we can say diseases are caused by pathogenic microbes. But not all diseases are caused by pathogens. So what could be the exact definition of disease? Any deviation from a normal state of health is called a disease when the functioning of one or more organs or systems of the body is adversely affected, characterised by the appearance of various signs and symptoms indicating poor health. Diseases are broadly grouped into infectious and non-infectious.

Types of Diseases

The human body suffers from various kinds of diseases. It can be due to infections, genetic disorders, or an unhealthy lifestyle. Broadly, diseases can be classified into two types namely, congenital and acquired diseases. Below we have explained the types of diseases in the following flowchart:

Types of Diseases

Fig: Types of Diseases

1. Congenital Diseases: Diseases that are present from birth or caused by mutation, chromosomal aberration or environmental factors are called congenital diseases. Some of the examples include alkaptonuria, sickle-cell anaemia, Down syndrome, Cleft palate, etc.
2. Acquired Diseases: Acquired diseases are the ones that develop after birth. These are not transferred from parent to offspring. Acquired diseases are also of two types, communicable (spread from one person to another) and non-communicable (not spread from person to person) diseases.

Following are differences between communicable and non-communicable diseases:

DescriptionCommunicable or infectious or contagious diseasesNon-communicable or non-infectious, or non-contagious diseases
DefinitionThese are transferred from one person to another.These diseases are not transferred from an affected person to a healthy person.
CausativeHighly infectious pathogens and vectors transmit these diseasesNot transmitted from one person to another through contact.
Agent causing infectionVirus, bacteria, worms, fungi, protozoans.No agents are involved  
Type of diseaseAs it develops immediately, it is acute.As it develops over a period of time and lasts forever, it is chronic
ExamplesCOVID-19, common cold, SARS, tuberculosis, typhoid, malaria, etc.Alzheimer’s disease. Epilepsy, cancer, heart diseases, diabetes, etc.

Common Diseases in Humans

As we have already learned, the disease-causing microorganism is called a pathogen. There are many ways through which these pathogens can enter our body, causing various types of diseases.
Some of the common diseases in humans are as follows:

Name of DiseasePathogen/ Causing agentVector/Mode of Transmission
Common Cold (nasopharyngitis, acute viral rhinopharyngitis, acute coryza)RhinovirusesThrough cough, sneeze and contaminated objects.
PneumoniaStreptococcus pneumoniae, Haemophilus influenzae, Mycobacterium pneumoniae (Bacteria)By inhaling droplets released by an infected person or using infected utensils
TyphoidSalmonella typhi (Bacteria)Through contaminated food and water, insects (houseflies, cockroaches, etc.), droplet infection and shared utensils and clothes.
MalariaPlasmodium falciparum, P. vivax, P. ovale, P. malariae (Protozoan)Through an insect vector- female Anopheles mosquito.  
Amoebiasis or Amoebic dysenteryEntamoeba histolytica (Protozoan)Through contaminated food, water and soil.
Dengue  Dengue virus (DENV)Through an infected Aedes aegypti mosquito.
AscariasisAscaris lumbricoides (Roundworms)  Through contaminated foods and drinks. Parasite’s eggs hatch inside the intestine of the new host. The larvae pass through various organs and settle as adults in the digestive system.
Filariasis/ ElephantiasisWuchereria bancrofti, Brugia malayi, Brugia timori. (Helminthes)Through female Culex mosquito.  
Ringworms (Dermatophytosis)Microsporum, Trichophyton, Epidermophyton (Fungi)Spread from the soil, using a towel, clothes or comb of an infected person. Close contact with an infected person is also a mode of infection.


The human body has the capacity to repair itself and to battle the assaulting microorganisms. The overall ability of the host to fight the disease-causing microbes or antigens due to the activity conferred by the immune system is called immunity. Immunity also includes defence against non-microbial antigens and malignancy. The most important characteristic of the immune system is that it differentiates self (body’s own cells) and non-cells (foreign molecules or invading cells). Any foreign substance invading the body and capable of stimulating the immune system is called an antigen. The protective chemicals produced by immune cells in response to antigens are called antibodies.

Types of Immunity

Immunity is of two types, innate immunity and acquired immunity. Following are further detail about these two types of immunity given as follows:
Innate Immunity or Inborn Immunity:
1. Innate Immunity is also called non-specific immunity or inborn immunity.
2. It is considered the first line of defence of the human body.
3. It is the natural defence mechanism of the human body.
4. It is not affected by prior contact with microorganisms or immunisation. e.g., skin, sebum, sweat, mucus and acids in the stomach are non-specifically protective.
5. Innate immunity comprises the various types of barriers that prevent the entry of foreign agents into the body, like cellular factors in innate immunity, fever, acute phase proteins (APPs), etc.

Acquired Immunity or Adaptive Immunity:
1. The resistance that an individual acquires during life is known as acquired immunity.
2. It is considered the second line of defence of the human body, and it is highly specific in function.
3. This immunity is conferred by the activity of lymphocytes.
4. To develop acquired immunity, prior contact with the specific antigen is essential.
5. It involves the formation of antibodies in the body, which neutralise the antigens.
6. Specific immunity may be active or passive.
7. Active immunity is the resistance developed by individuals as a result of an antigenic stimulus.
8. Passive immunity is acquired when ready-made antibodies are received by the body cells.
9. Active and passive immunity can be acquired either naturally or artificially.

Types of Immunity

Fig: Types of Immunity

Cells of Immune System

The human immune system consists of lymphoid organs, tissues, cells and protein molecules like antibodies.
Lymphoid organs: These are the organs where the origin and/or maturation and proliferation of lymphocytes occur.
Primary lymphoid organs include bone marrow and thymus, where B-lymphocyte and T-lymphocyte cells develop, mature and acquire their antigen specificity.
Secondary lymphoid organs are the ones where lymphocytes interact with the antigen and proliferate to become effector cells. Secondary lymphoid organs include the spleen, lymph nodes, tonsils, Peyer’s patches of small intestine and appendix. Following are the important organs and their functions:
1. Bone Marrow: Main lymphoid organ where lymphocytes are produced, and B-lymphocytes mature.
2. Thymus: Lobed organs located near the heart and beneath the breastbone; their size reduces with age. They are the site where T-lymphocytes mature.
3. Spleen: Large bean-shaped organ that acts as a filter of blood and reservoir of RBCs. It is the largest lymphoid organ.
4. Lymph Nodes: These are small solid structures located at different points along with the lymphatic system. They trap the antigens and invoke the immune response.
5. Mucosa-associated Lymphoid Tissue (MALT): Located within the lining of the major tracts such as respiratory, digestive and urogenital tracts. It constitutes 50% of lymphoid tissue.

Organs of Immune System

Fig: Organs of Immune System

Vaccination and Immunisation

Administration of vaccines, i.e. inactivated pathogen or antigenic protection of pathogen to protect against a particular pathogen, is called vaccination.
1. Memory B-cells and T-cells are produced by vaccines that quickly recognise the pathogen and neutralise the invader by various mechanisms.
2. If the preformed antibodies against any antigen are introduced into the body, it is called passive immunisation.
3. Vaccination has allowed us to control diseases like measles, polio, tetanus and whooping cough that once threatened many lives.


  1. An overactive or exaggerated response of the immune system to a certain antigen or pathogen is called an allergy.
  2. The substances which cause allergies are called allergens.
  3. Most common examples of allergens are pollen, dust, animal dander, mites in dust, insect stings, food, medicine, etc.
  4. Allergies can cause a variety of symptoms like runny nose, itching, rashes, sneezing, swelling or asthma.
  5. Allergies can range from minor to major.
  6. Anaphylaxis is a severe case of allergy that can be life-threatening.
  7. Allergy can be treated by using medicines, allergy shots, and by avoiding the substances that cause the reactions.

Autoimmune Diseases

  1. Autoimmune diseases are diseases in which the immune system of the body is unable to differentiate between self and foreign substances and start killing off the body cells and tissues.
  2. Autoimmune diseases may occur due to various reasons, among which genetic factor is a major one.
  3. Some autoimmune disease targets only some organs, for example, In Juvenile type 1 diabetes, the immune system targets and damages the pancreas.
  4. Other autoimmune diseases like systemic lupus erythematosus (SLE) target the entire human body.
  5. Some other examples of autoimmune diseases are rheumatoid arthritis, coeliac disease, multiple sclerosis, vasculitis, etc.
Examples of Autoimmune Diseases

Fig: Examples of Autoimmune Diseases

Acquired Immunodeficiency Syndrome

AIDS, the Acquired Immunodeficiency Syndrome, is usually a fatal disease caused by a retrovirus known as Human Immunodeficiency Virus (HIV). HIV weakens the body’s immune system, leaving the victim vulnerable to life-threatening opportunistic infections, neurological disorders and unusual malignancies. Unexplained diarrhoea lasting longer than a month, fatigue, malaise, loss of more than 10 percent body weight, fever, night sweats, etc., are some of the clinical signs of AIDS.  Diagnosis is made by Enzyme-linked immunosorbent assay (ELISA). There is no vaccine for AIDS. The use of antiretroviral drugs is one of the effective treatments.
Following are modes of transmission and preventive measures for the disease:

Modes of TransmissionPreventive Measures
Sexual contact with an infected personEducation and awareness about AIDS transmission
Transfusion of contaminated blood and blood products.Use of disposable needles and syringes
Sharing infected needles, as in the case of intravenous drug abusers.Sexual habits should be safe and cautious
From an infected mother to her child through the placenta.High-risk individuals should not donate blood
The onset of the disease may take a few months or years (5-10 years).Screening for HIV during blood transfusions
Transplantation with infected organsRoutine screening for donors, patients undergoing haemodialysis and pregnant women.


Cancer is a medical condition in which some of the body cells grow abnormally and uncontrollably. These damaged cells may form lumps of tissues called tumours. Tumours can be cancerous or non-cancerous. Tumours are of two types, Malignant or cancerous tumours or non-localised tumours and Benign tumours or non-cancerous tumours or localised tumours.

Causes of CancerTreatment of Cancer
Several chemicals like nicotine, caffeine, products of combustion of coal and oil, some sex hormone, and steroids may cause cancer.Chemotherapy uses anticancer drugs to kill cancer cells.
The x-rays, gamma-rays, cosmic rays, ultra-violet rays etc., are carcinogenic.Radiotherapy or radiation therapy uses high-powered energy beams, such as X-rays or protons to kill cancer cells.
Viruses causing cancer have genes called viral oncogenes (v-onc genes). They are also called oncogenic viruses, e.g., EBV (Epstein-Barr virus), HPV (Human papillomavirus), etc.The entire cancerous tissue or cells are removed surgically.  
Genes called cellular oncogenes (c-onc genes) or proto-oncogenes have been identified in normal cells, which, when activated under certain conditions, could lead to oncogenic transformation of cells.Immunotherapy or biological therapy uses our body’s immune system to fight cancer. It activates the immune system and helps in destroying the tumour. Immunomodulators like alpha-interferons can be given for the treatment of various types of cancer.
Different types of addictions like smoking, chewing tobacco lead to cancer of the mouth and lungs. Alcohol consumption may result in cancer of the oesophagus, stomach, intestine and liver. Drugs also cause cancer, e.g. Marijuana, anaerobic steroids etc.Supportive therapy is used to treat symptoms of cancer and the side effects of cancer treatments.

Adolescence and Drug/Alcohol Abuse

  1. The World Health Organisation (WHO) defines adolescence as the period of life between 12 and 19 years of age. The adolescence phase is also called teenage.
  2. Teenage is considered as the crucial phase of life as lots of physical as well psychological changes occur.
  3. Most teenagers can be influenced by external and internal factors, which makes them vulnerable to alcohol and drug use.
  4. Once they get used to drugs and alcohol, it might be possible that they got addicted to them, resulting in drug and alcohol abuse.
  5. The drugs, which are commonly abused, are opioids, cannabinoids and alkaloids of cocaine.
Adolescence and Drug/Alcohol Abuse

Fig: Adolescence and Drug/Alcohol Abuse

Effects of Alcohol and drug abuse:
1. May cause extreme rough behaviour. A very high dosage might lead to death.
2. Alcohol or drug abused people commonly become dull, antisocial, depressed, tired, aggressive, etc.
3. Consumption of intravenous drugs might lead to the transmission of many infectious diseases like AIDS and Hepatitis B if the same syringe is shared among multiple people.
4. Excessive alcohol usage ultimately leads to the failure of a vital organ like the liver.
5. Cocaine, Morphine, Heroin, Datura and Atropa belladona are some commonly used drugs.
Drug and alcohol abuse is rampant among the youth. Below are some examples of drugs are their effects on the consumer:

Type of DrugExamplesEffects
Sedatives and tranquiliser (depressants)Benzodiazepines (e.g., valium), barbituratesDepressing brain activity creates a feeling of calmness and relaxation, drowsiness, and deep sleep under high doses.
Opiate narcoticsOpium, morphine, heroin, pethidine, methadoneSuperbrain activity provides relief from intense pain.
StimulantsCaffeine (very mild), cocaine, amphetamines.It stimulates the nervous system, makes a person more alert, wakeful and provides excitement.
HallucinogensLSD, mescaline, psilocybin, charas, bhang, Marijuana, hashish (cannabinoids)Alerts thoughts, feelings and perceptions.
NicotineAn alkaloid present in tobaccoIt stimulates the release of adrenaline and nor-adrenaline into blood circulation, both of which raise blood pressure and increase heart rate. It can cause cancers of the lung, urinary bladder and throat, bronchitis, emphysema, coronary heart disease, gastric ulcer, etc.

Prevention and control:
1. Counselling and education play a very important role while dealing with cases of smoking, alcohol and drug abuse.
2. Medical help should be provided when counselling and talking cannot help.
3. Avoidance of peer pressure could help in bringing down these habits to a large extent.
4. Help from family and friends could do a lot of damage control.
5. There are many rehabilitation centres mainly launched to help alcohol and drug abuse patients.


The state of complete physical, mental and social well being is called health. On the contrary, any deviation from a normal state of health is called disease. Diseases can be of two types, congenital and acquired. Diseases that are present from birth or caused due by mutation, chromosomal aberration or environmental factors fall under congenital diseases. Acquired diseases are the ones that develop after birth and are not transferred from parents.

These are also of two types, communicable (spread from one person to other) and non-communicable (not spread from person to person) diseases. Disease-causing microorganisms are called pathogens. The ability of our body to fight these pathogens is conferred by the immune system and called immunity. Immunity is of two types, innate immunity (present at the time of birth) and acquired immunity (acquired during the lifespan). Acquired immunity can be active or passive. The human immune system consists of lymphoid organs, tissues, cells and protein molecules like antibodies.

Vaccination is a passive immunisation technique used to prevent many deadly diseases. Allergy is an overactive or exaggerated response of the immune system to a certain antigen or pathogen called allergens. Diseases in which the immune system of the body is unable to differentiate between self and foreign substances and start killing off the body cells and tissues are called autoimmune diseases. Adolescence or teenage is the period of life between 12 and 19 years of age. At this age, individuals are more susceptible to falling into the trap of smoking, alcohol or drug abuse. Strong emotional support and certain preventive measures help to deal with the problem.

FAQs on Human Health and Diseases

Q.1. What is human health and disease?
Ans: The state of complete physical, mental and social well being is called health, while any deviation from a normal state of health is called disease. Both of these concepts are directly related to each other. A person suffering from a disease cannot be called healthy.

Q.2. What are the types of diseases?             
Ans: Diseases can be of two types, congenital and acquired.
1. Diseases that are present from birth or caused by mutation,  chromosomal aberration or environmental factors are congenital diseases.
2. Acquired diseases are the ones that develop after birth and are not transferred from parents; these are also of two types, communicable (spread from one person to other) and non-communicable (not spread from person to person) diseases.

Q.3. What is the main cause of health problems?
Ans: Health problems are mainly caused by a person’s genetic make-up, his/her lifestyle behaviours (e.g., drinking alcohol, smoking), exposure to toxic substances (e.g. pathogens, allergens, etc.) or any other reasons.

Q.4. How can we improve our health?
Ans: Eating a healthy diet, regular exercise, yoga, meditation, and regular health check-ups are some of the important factors that help us to improve our health.

Q.5. What is considered a vaccine?
Ans: Vaccines are products that induce immunity to a specific disease. Vaccines are inactivated pathogens or antigenic protection of pathogens that are used to protect the body against a particular pathogen. This process is called vaccination.

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