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What is Illness: Symptoms, Causes, Diagnosis, and Treatment

Definition and Overview

Illness is a broad term that defines the poor state of mind, body, and, to a certain extent, spirit. It is the general feeling of being sick or unwell (outside the person’s belief of good health).

Many people tend to use disease and illness in the same breath, but there are very subtle distinctions. Disease refers to the affliction of a specific organ or the entire body due to a harmful microorganism such as bacteria or virus, injury, chemical imbalances in the body, exposure to toxins, and production of immature cells. Examples of diseases are cancer, fractures, diabetes, cirrhosis, and psoriasis, among others. The same thing goes for mental health issues such as bipolar disorder, clinical depression, and schizophrenia.

Illness, on the other hand, is the reaction of the body to the disease. It represents fatigue, fever, muscle weakness, or blurred vision, as well as abnormal blood pressure and a rapid heart rate. It should be noted though that illness, or the feeling of being unwell or sick, can occur even without a disease.

Another distinction between a disease and an illness is its specificity. A disease is based on specific factors or criteria that doctors are looking for when a patient goes into the clinic or hospital to be examined. An illness, meanwhile, can refer to any disease. Also, because it’s largely a feeling, it can be different among patients.

Causes of Condition

An illness can be caused by a number of factors such as the following:

  • The presence of diseases – Usually, illness occurs because the body has an underlying disease. The body is designed to provide a natural response to any abnormality or threat, whether it’s a bacterium, virus, or excessive production of immature cells. But in the process, such reaction can make a person feel sick. A good example is allergy. Allergy develops when the immune system tries to kill the threat and releases histamines in the process. Nevertheless, a person may also have a disease but not feel unwell. Diseases such as HIV, AIDS, and even cancer can take months or years before they progress and make a person feel unwell.

  • Hypochondriasis – Hypochondriasis is the reason why people can “feel ill” even without a disease. This is a condition that refers to the abnormal or moderate to severe anxiety of having a disease. A simple change in the body temperature may be considered by a hypochondriac as a fever or a symptom of a serious disease like cancer. Hypochondriasis is further fueled these days by the Internet. A person can now quickly and easily search for symptoms or self-diagnose.

  • Stress – Stress is a natural response of the body to a trigger. The body is designed to take either a fight-or-flight mode when in a stressful situation. Either way, it can increase the heart rate, blood pressure, and can lead to the production of a hormone called cortisol, which can make a person ill when stress becomes chronic.

  • Malnutrition – As a complex structure, the body needs different kinds of enzymes, vitamins, minerals, and other macro and micronutrients to function properly. In the long term, if the body becomes deficient in any of these, it can feel ill.

In alternative medicine, such as CTM (Chinese traditional medicine), an illness may be caused by a blockage of the energy flow (qi).

Key Symptoms

Illness has ambiguous symptoms such as:

  • Dizziness
  • Diarrhea
  • Chest pain (or any type of pain)
  • Anxiety
  • Fatigue
  • Abnormal heart rate and blood pressure
  • Blurred vision
  • Tremors

These symptoms may refer to several kinds of diseases, or they may have been exaggerated depending on how a person defines his illness.

Who to See and Types of Treatment Available

A general doctor (or GP) is the first person who can diagnose and treat an illness. For children, the doctors are referred to as paediatricians. Adults, on the other hand, can look for an internist.

During the initial consultation, the doctor takes note of the patient’s medical and even family history, symptoms, and overall feeling. Standard tests are then requested for a more accurate diagnosis. These can include CBC or other blood tests, urinalysis, stool analysis, and X-ray. If the results are inconclusive or not sufficient to make a diagnosis, more comprehensive examinations like CT or MRI scans, ultrasound scans, and probes (e.g., colonoscopy, endoscopy, etc.) may be performed.

Based on the symptoms, history, and results of the exams, the doctor then makes a diagnosis. Depending on the condition, the doctor can formulate a treatment plan or refer the patient to other specialists such as orthopedists, physical therapists, cardiologists, neurologists, oncologists, and nephrologists.

For those who are suffering from hypochondriasis, it’s essential they receive the right mental support or counseling from psychologists as the high level of anxiety may compel them to undergo unnecessary and sometimes risky medical exams and treatments.

An illness, however, has its own risk. Since it’s a general feeling and something more personal, a person may feel well even if the disease is still present. This explains the significant role a person’s mental state has over the body, as well as how a placebo (also called a dummy or a harmless pill) can alter an illness.

The feeling of wellness even with the presence of disease can lead to drug resistance in the future. Patients will stop taking the medications as soon as better health is felt. By then, however, the bacterium or virus is not completely killed. Worse, it can mutate and adapt to the drugs. This may also prevent them from seeking medical intervention.

It’s therefore important that health providers perform more than diagnosing a disease. They must also encourage their patients to seek regular screenings even in the absence of an illness. This way, diseases can be caught in the early stages. Doctors should also educate the patients, helping them correctly assess their abnormal feelings. This can prevent them from demanding unneeded treatment.


  • Center for Disease Control and Prevention. http://www.cdc.gov/