Infectious diseases are caused by microscopic germs (such as bacteria or viruses) that get into the body and cause problems. Some — but not all — infectious diseases spread directly from one person to another. Infectious diseases that spread from person to person are said to be contagious.
Some infections spread to people from an animal or insect, but are not contagious from another human. Lyme disease is an example: You can't catch it from someone you're hanging out with or pass in the street. It comes from the bite of an infected tick.
Contagious diseases (such as the flu, colds, or strep throat) spread from person to person in several ways. One way is through direct physical contact, like touching or kissing a person who has the infection. Another way is when an infectious microbe travels through the air after someone nearby sneezes or coughs.
Sometimes people get contagious diseases by touching or using something an infected person has touched or used — like sharing a straw with someone who has mono or stepping into the shower after someone who has athlete's foot. And sexually transmitted diseases (STDs) are spread through all types of sex — oral, anal, or vaginal.
You can help protect yourself against contagious diseases by washing your hands well and often, staying away from those who are sick, making sure you're up to date on all vaccinations, and always using condoms during any type of sex.
Reviewed by: Larissa Hirsch, MD
Date reviewed: June 2014
*Names have been changed to protect user privacy.
|National Institutes of Health's National Institute of Allergy and Infectious Diseases (NIAID) The National Institute of Allergy and Infectious Diseases (NIAID) conducts and supports basic and applied research to better understand, treat, and ultimately prevent infectious, immunologic, and allergic diseases.|
|Centers for Disease Control and Prevention (CDC) The CDC (the national public health institute of the United States) promotes health and quality of life by preventing and controlling disease, injury, and disability.|
|CDC: Preteen and Teen Vaccines CDC site provides materials in English and Spanish for parents, teens, preteens, and health care providers about vaccines and the diseases they prevent.|
|GYT - Get Yourself Talking and Get Yourself Tested This media campaign designed to get young people to talk with their health care providers and partners about the importance of getting tested for sexually transmitted diseases.|
|Hand Washing Did you know that the most important thing you can do to keep from getting sick is to wash your hands? If you don't wash your hands frequently, you can pick up germs from other sources and then infect yourself.|
|Why Should I Care About Germs? Germs are tiny organisms that can cause disease - and they're so small that they can creep into your system without you noticing. Find out how to protect yourself.|
|Flu Center Get the basics on how flu spreads and how to protect yourself.|
|About Sexually Transmitted Diseases (STDs) You've probably heard lots of discouraging news about sexually transmitted diseases. The good news is that STDs can be prevented. Find out how to protect yourself.|
|Immunizations Missing out on shots puts you at more serious risk than you might think. That one little "ouch" moment protects you from some major health problems.|
|About Birth Control Before you consider having sex, you need to know how to protect yourself. Read this article to get the basics on birth control.|
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