An Overview of Infections

Medically Reviewed By Darragh O'Carroll, MD
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An infection occurs when a pathogen or microorganism invades the body and multiplies. Common pathogens include bacteria, viruses, and fungi. When these pathogens establish themselves in your body, they can damage your tissues or organs and make you ill. Treatment will depend on the type of infection and severity of your symptoms.

Read on to learn more about the types, symptoms, treatments, and prevention methods for infections. 


Hands holding a microscopic sample and a swab
VICTOR TORRES/Stocksy United

An infection occurs when a pathogen uses your body as a host to nourish itself and reproduce. A pathogen is an organism that can cause illness or disease.

Infections can affect anyone and occur anywhere in the body. Infectious diseases are also called communicable diseases. Pathogen transmission can happen via: 

  • contact with a person or surface that carries the infection
  • inhalation 
  • sprays or splashes 
  • skin punctures, including from sharp objects or animal bites
  • ingestion 

Most of the time, your immune system can manage minor infections. More severe infections can overwhelm your immune system, releasing toxins or inflammatory chemicals that can elicit a negative response within your body. 

Doctors can treat some infections, but a few varieties are resistant to treatment. Therefore, prevention is often the best defense against most infectious diseases. 

How an infection spreads and the harm it causes can vary based on the type of pathogen.

Bacterial infections

Bacteria are organisms with only a single cell. If you view bacteria under magnification, they look like spirals, rods, or balls.

Bacteria are all around us. They can survive extreme environments, including harsh cold, heat, and radioactive waste. 

Not all bacteria will make you ill. Some are beneficial. Infectious bacteria can make you sick, reproducing rapidly and secreting toxins. There are several serious infections that develop from strains of lethal bacteria, including: 

Other bacterial infections that can make you ill include: 

Symptoms of bacterial infections

Depending on the type and location of the infection, people with bacterial infections may experience:

  • fever
  • inflammation
  • swelling
  • skin discoloration
  • pain
  • heat at the infection site

When bacteria enter your body, they will attempt to multiply rapidly. As a result, the bacteria can interrupt typical bodily functions, produce toxins that are harmful to your cells, or damage your tissues.

Treatments for bacterial infections

Doctors commonly use antibiotics to treat bacterial infections. These medications remove bacteria or significantly impair their ability to replicate. They can come in oral, topical, or intravenous forms.

However, some bacterial strains can become resistant to certain classes of antibiotics. This may make an infection more difficult to treat.

Viral infections 

Viral infections are other main types of infections. A viral infection occurs when you develop an infection due to contracting a virus. Viruses are not as big as bacteria. But like bacteria, there are numerous different kinds of viruses.

A virus contains a piece of genetic code, a coating of protein, and protective fat molecules called lipids. When a virus enters your body, it attaches to a cell so it can break into the cell and deposit its genetic code.

Once a virus deposits genetic code, in most cases, this forces the cell to replicate the virus, which causes the cell to die. When the cell dies, it releases additional viruses that can continue replicating inside your body, making you sick. 

If the cell does not die, such as in the case of human papillomavirus (HPV), the virus will permanently alter its function. Sometimes, this results in unmanageable cell replication, which may lead to cancer

Viruses can remain dormant or inactive in your body and then reactivate at a later time. Viruses can also affect specific populations, such as infants or older adults.

Common viral infections include: 

Symptoms of viral infections

Viral infection symptoms can include:

Treatments for viral infections

Treatment for viral infections typically focuses on managing the symptoms. Some people may benefit from antiviral medications, while others can take over-the-counter pain relievers.

Fungal infections

There are many forms of fungi. Most fungi are multicellular parasites that use enzymes to break down and absorb organic matter, like mushrooms. Single-celled fungi, such as yeasts, can exist independently or in a colony. Most fungi release spores to spread and multiply. 

Fungal infections frequently affect the skin and lungs due to spores in the air that can land on you or enter your lungs through respiration.

While anyone can get a fungal infection, people with weakened immune systems may be more likely to get them.

Types of fungal infections include: 

Symptoms of fungal infections

Many symptoms of fungal infections relate to the skin and may include:

  • sensation of burning or stinging
  • itchiness
  • blisters
  • rash
  • discoloration
  • discharge

Internal fungal infections may cause symptoms like headache, fever, or stiffness in the neck.

Treatments for fungal infections

Doctors may treat fungal infections on the skin and nails with topical antifungal medication. For internal infections, oral antifungals can be beneficial.

Prion diseases

Prion diseases are rare infections in which the host’s regular prion protein malfunctions and creates prions that cause infectious brain disease.

Typically, the prion proteins are harmless. They are not living microorganisms and do not have genetic proteins. It is only when they malfunction by folding into an atypical shape that they become harmful. 

Instead of replicating or feeding on host tissue, prions make other proteins, and cells in your body behave unusually. They generally affect the brain and nervous system. The result is degenerative brain diseases, including: 

  • Gerstmann-Straussler-Scheinker disease
  • Creutzfeldt-Jakob disease
  • fatal familial insomnia

Prion diseases only affect mammals, including humans.

Symptoms of prion diseases

Prion diseases can cause neurological health concerns, such as:

  • memory loss
  • changes in walking patterns
  • hallucinations
  • difficulty speaking

A doctor may also spot plaque buildup in the brain.

Treatments for prion diseases

There are currently no treatments available that can cure prion diseases or slow disease progression. Prion diseases are usual fatal.

Other types of infections 

There are various other types of infections in addition to the three kinds mentioned above.

Ectoparasites, like ticks or lice, can cause an infection when they burrow into or bite the skin. Other single-celled organisms may cause a protozoan infection. Multicellular organisms and parasites like ringworm can cause infections as well.


Prevention is critical when it comes to infections. While there is no guaranteed way to protect yourself against all infectious diseases, you can reduce your risk with the following methods: 

  • Wash your hands frequently, especially before touching or eating food and after using the bathroom.
  • Stay up to date on vaccinations that your doctor recommends. 
  • Clean surfaces regularly and sanitize any that come into contact with germs, such as from raw meat. 
  • Follow food storage and preparation safety guidelines. 
  • Reduce your risk of sexually transmitted infections through sexual abstinence, having sex using a condom or another barrier method, or undergoing regular screening. 
  • Avoid sharing personal items like water bottles, toothbrushes, and razors. 
  • Follow medical advice when you have an infectious disease to avoid passing it on to others. 

Keeping your immune system strong by maintaining a healthy lifestyle and eating a balanced diet can help your body clear out invading pathogens that can cause infections. 


Organisms that may cause infections are all around us. While there is no way to avoid pathogens altogether, prevention methods can help keep harmful ones from entering your body and making you sick.

Contact your doctor to discuss ways to prevent infections.

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Medical Reviewer: Darragh O'Carroll, MD
Last Review Date: 2022 Sep 20
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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