How You May Get an Infection

How pathogens enter the body

Everyone gets infections of some sort or another. Colds, oozing pus, and other ordinary discomforts are all results of infection. Other infections are not so benign. For example, some viral or bacterial infections can be life-threatening. HIV, for example, is an infection that can be deadly.

But how do infection-causing pathogens enter the body? Understanding the four main ways that infections start can help you protect yourself.

Adult on couch blowing his nose
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The Respiratory Tract

Another name for the common cold is an upper respiratory infection. It occurs when one of 200 different cold-causing viruses is breathed in and enters the respiratory tract. Rhinoviruses are the most common of the viruses that cause colds. Influenza, and other infections that spread through the air are also contracted in this fashion. To protect yourself, try to avoid close contact with others who have upper respiratory infections.

Mucous membranes that line the mouth or nose also provide a route for infection to enter.

Colds and flu don't typically affect the lungs directly, but they may lead to another (secondary) bacterial infection called pneumonia.

Skin Contact

One of the many functions of the skin is to act as a barrier against infection. However, if you have a cut, scratch, bug bite, or any type of open wound, the germs that your skin is meant to keep out can enter your bloodstream. Though some infections such as herpes start through skin contact alone—without a break in the skin layer.

Common infections that start through skin contact in the skin include:

  • Cellulitis: When bacteria (usually streptococcal bacteria) enter your body through a cut, burn, wound or surgical incision, you may get a potentially dangerous infection called cellulitis. Skin will become red, inflamed and painful, and you may experience fever, fatigue or chills. Antibiotics can treat the infection before it spreads into your bloodstream.
  • Impetigo: Usually caused by staph or strep bacteria, impetigo is a very contagious bacterial skin infection. It is the most common type of skin infection in children and does not affect adults nearly as often. Impetigo doesn't require a break in the skin layer, but it is more likely to occur if there's a break in skin.

In some cases, it's possible to protect yourself from infection through the skin. Wearing protective clothing when in the woods, for example, can make a big difference because it prevents bites from ticks that can carry and spread infections such as Lyme disease.

The Digestive Tract

Food, drink or other products infected with bacteria or a virus can be swallowed and infect the stomach or bowels. Most people have experienced an upset stomach at one point in their life, which sometimes reveals itself in the form of diarrhea and/or vomiting. A common example of this is bacterial gastroenteritis, otherwise known as food poisoning. You can get food poisoning if you eat meat or poultry that came in contact with bacteria during processing, or if produce has touched water during growing or shipping that contained animal or human waste. Improper food handling can also be a source of infection–leaving food unrefrigerated too long, or poor sanitary conditions.

The Urinary and Reproductive Systems

Pathogens can also enter the body through the urinary system, as is the case of a urinary tract infection, or the reproductive system, as is the case with sexually transmitted diseases. The infectious agent may remain localized or may enter the bloodstream. For example, sexually transmitted diseases most commonly infect the genitals, while HIV is carried in bodily fluids and can be transmitted in saliva, seminal fluid, or blood.

3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Scallan E, Hoekstra RM, Angulo FJ, et al. Foodborne illness acquired in the United States--major pathogens. Emerging Infect Dis. 2011;17(1):7-15. doi: 10.3201/eid1701.P11101

  3. Flores-mireles AL, Walker JN, Caparon M, Hultgren SJ. Urinary tract infections: epidemiology, mechanisms of infection and treatment options. Nat Rev Microbiol. 2015;13(5):269-84. doi:10.1038/nrmicro3432

Additional Reading

By Jerry Kennard
 Jerry Kennard, PhD, is a psychologist and associate fellow of the British Psychological Society.