12 Things You Think Are Contagious—But Aren’t
Just because something looks bad doesn't mean it's contagious—and that includes these icky diseases, disorders, and infections
How can you tell if something’s contagious?
If you’re not sure what condition someone has and you’re not a health care professional, you probably won’t be able to tell if something is contagious. Visible symptoms for contagious and non-contagious diseases sometimes can seem identical, and the mode of transmission depends on the particular disease. “There is not a single relationship between the cause of an infection and its contagiousness, as there are bacterial diseases that are contagious and others that are not,” explains Amesh Adalja, MD, an infectious disease physician and Senior Scholar at the Johns Hopkins Center for Health Security, adding that the same is true for the world’s smorgasbord of viruses.
And then there are the conditions caused by a malfunctioning immune system or environmental factors. The bottom line: It’s never a bad idea to take safety precautions. “Overall,” says Dr. Adalja, “being vaccinated and frequent handwashing are good practices regardless.” (Check out these 10 ways you’re washing your hands wrong.)
Whether or not this lung infection is contagious depends on what caused it. Two types of pneumonia that can’t be spread from person to person are fungal pneumonia and aspiration pneumonia. Fungal pneumonia is contracted from the environment and aspiration pneumonia happens when food or liquid is inhaled into the lungs.
On the other hand, bacterial and viral pneumonia—which cause most cases of pneumonia, according to the American Lung Association—are indeed contagious, though not in the way you might think. “The causative microorganism may move between people but may not automatically cause pneumonia,” says Dr. Adalja. “For example, some bacteria may just colonize the nasal passages, while influenza, which can cause pneumonia, may cause bronchitis in another individual.” (Check out these signs your upper respiratory infection is actually pneumonia.)
An outbreak doesn’t always result from an infected person or animal. In the case of Legionnaires’ disease, a contaminated water supply is the culprit. Transmission only happens when a person inhales mist or water droplets that contain Legionella bacteria. According to the National Institutes of Health, exposure can come from faucets, showers, whirlpools, and the ventilation systems of large buildings. While this rare form of pneumonia can be severe and deadly, not everyone who is exposed to the bacteria will contract the disease. People at particular risk include those over 50, especially if they have a weakened immune system or chronic illness.
This skin disorder that affects around 2 percent of Americans has nothing to do with germs or bacteria, and it is not contagious. “Psoriasis is an autoimmune condition in which the immune system attacks the skin,” explains Dr. Adalja. “It is not caused by a microorganism that can be passed between people.”
Telltale signs include red, itchy patches of skin topped by white or silvery scales that are often found on the elbows, knees, and scalp. They occur when the body creates and accumulates new skin cells too quickly. (Don’t miss these 6 surprising signs of disease your skin can reveal.)
The good news: You can’t catch an ear infection. The bad news: If a germ caused this painful malady instead of, say, water in your ears, you can catch that germ responsible—and the most common culprit is a cold virus.
“Due to congestion caused by the cold, the inner ear fills up with fluid and can become secondarily infected by bacteria; these stay in the ear and are therefore not contagious,” explains Matthew Mintz, MD, clinical associate professor of medicine at the George Washington University School of Medicine and an internal medicine and primary care doctor in Bethesda, Maryland. “However, since the ear infection started with a cold, if the patient still has cold symptoms, they can still be contagious.”
While ear infections can affect people of all ages, they more commonly hit children. Ear infections account for around 30 million trips to the pediatrician each year in the United States. (Here are 6 earache and ear infection remedies every parent should know.)
This non-contagious skin condition causes redness, visible blood vessels in the face, and sometimes small bumps and acne-like breakouts. Less commonly, rosacea can also lead to a thickening of the skin on the nose. While experts aren’t sure what causes this condition—which hits approximately 14 million Americans—they theorize that genetics, abnormal facial blood vessels, and possibly even the gut bacteria H. pylori may play a role.
The National Rosacea Society explains that antibiotics used to treat rosacea may be effective because they help to combat inflammation, not because they’re killing bacteria. (Learn 10 more things to know about rosacea.)
Much like pneumonia, some forms of bronchitis are contagious and others are not. It depends on what’s causing the inflammation of the bronchial airways and the resulting coughing, wheezing, and general breathing difficulties. Acute bronchitis, which usually results from an upper respiratory infection that travels to the chest, is often caused by a virus and is contagious. Hundreds of viruses, as well as some bacteria, can potentially lead to bronchitis, and you can catch them when germs enter your mucous membranes through your eyes, nose, or mouth. This man developed a deadly lung infection after taking a trip inside a cave.
Chronic bronchitis, however, isn’t contagious. This ongoing condition is often caused by long-term smoking or exposure to environmental pollutants. (Be aware of these 12 silent signs that your lungs could be in trouble.)
Infected ticks are the only contagious things you need to worry about in terms of Lyme disease, according to the Centers for Disease Control and Prevention (CDC). And that’s only if they attach to your body and feast on your blood. That means that you can’t catch this bacteria-based disease from other people, whether it’s through casual contact, kissing, or even sex. Pets can’t infect you either, though they can carry ticks into your home.
Fever, fatigue, and a distinctive bull’s eye rash around the infected site are among the early symptoms of Lyme disease. Later on, you may develop severe joint pain, debilitating headaches, tingling in your hands or feet, and brain and spinal cord inflammation. (These are the 18 signs of Lyme disease people often miss.)
Poison ivy rash
Just looking at a poison ivy rash may make you feel itchy, but it’s all in your head. A poison ivy rash cannot be transmitted to another person, even if you touch the rash or the fluid from a blister. Transmission can only happen if your skin comes in contact with the plant’s oil—called urushiol. That can happen either through direct contact with the oil or if it gets on your clothing or pets—and then you touch them.
Wondering if that rash is poison ivy? It will often show up in a straight line, if you’ve brushed up against the plant. However, if it’s gotten onto your clothing or your pup’s fur, the rash might be more haphazard and expansive. Here’s how to recognize the poison ivy plant.
This potentially deadly infectious disease can’t be transmitted from person to person. You get it from mosquitoes. When they bite you, they release the malaria parasites into your bloodstream. You’ll get symptoms like fever, flu-like symptoms, gastrointestinal issues, and jaundice. However, malaria infects red blood cells, the CDC warns, and that means you could get it through a blood transfusion, by sharing an infected needle, or during pregnancy or childbirth. Mosquitoes aren’t the only insects you need to watch out for. (These are 8 bug bites that need medical attention—now.)
Urinary tract infections
While urinary tract infections (UTIs) often pop up after sex, they are not sexually transmitted or otherwise contagious. Instead, they occur when bacteria, often from the anus, enters the urethra. “Sexual intercourse can increase this spread, but this is through physical contact that helps contaminate the urethra,” explains Dr. Mintz, “not from an infection spreading from one partner to another.”
He adds that women tend to get UTIs more frequently than men because of the close proximity of these two body parts. What’s more, the infection can happen in a lot of different ways—not just via intercourse. Be sure to be on the lookout for the symptoms of a urinary tract infection everyone should know. If you’re battling a UTI, you may want to avoid sex to prevent discomfort and allow your body to heal.
The scarier, more colloquial term for tetanus, lockjaw causes intense muscle spasms and a “locking” of the jaw, which makes it difficult to open your mouth or swallow. But infected people aren’t contagious. Instead, the bacteria responsible for this disease live in the environment, in soil, and on many surfaces, and enters the body via broken skin, according to the National Foundation for Infectious Diseases.
The CDC points out that likely ways to get tetanus are through puncture wounds (like from stepping on a nail), wounds that get dirty, burns, or crush injuries. People can protect themselves against tetanus with a vaccine, followed by booster shots every 10 years. (Check out these 40 things your doctor wishes you knew about vaccines.)
You need to take cellulitis seriously since it can cause life-threatening bacteremia or endocarditis. But you generally don’t have to worry about transmitting it to someone else. That’s because this infection is caused by bacteria that live on your skin—and are often harmless: Group A strep are the most common cause. It’s only a problem when the bacteria penetrate deep through breaks in your skin.
“If there is damage—either from a cut, recent surgery, or even athlete’s foot—that damage can allow in bacteria, which can affect the deeper layers of the skin,” explains Dr. Mintz. This can result in a serious infection characterized by pain, redness, swelling, tenderness, and fluid-filled blisters. “There are generally no precautions that need to be taken [to prevent transmission],” adds Dr. Mintz, “though if there is pus or oozing fluid, which is not typical in cellulitis, this material can spread infection.”
Infections aren’t the only things you need to worry about catching. Check out these 11 things you didn’t know were contagious.
- Amesh Adalja, MD, an infectious disease physician and Senior Scholar at the Johns Hopkins Center for Health Security
- Medscape: “Fungal Pneumonia”
- Medscape: “Aspiration Pneumonitis and Pneumonia”
- American Lung Association: “Learn About Pneumonia”
- National Institutes of Health Genetics and Rare Diseases Information Center: “Legionnaires’ disease”
- American Academy of Dermatology Association: “Psoriasis: Causes”
- Matthew Mintz, MD, clinical associate professor of medicine at the George Washington University School of Medicine and an internal medicine and primary care doctor in Bethesda, Maryland
- Boston Children’s Hospital: “Ear Infection”
- American Academy of Dermatology: “Rosacea”
- National Institutes of Health: “Understanding Rosacea”
- National Rosacea Society: “Frequently Asked Questions”
- American Academy of Family Physicians: “Acute Bronchitis”
- MedlinePlus: “Chronic Bronchitis”
- Centers for Disease Control and Prevention: “Lyme Disease”
- KidsHealth: “Poison Ivy”
- Centers for Disease Control and Prevention: “Malaria”
- National Foundation for Infectious Diseases: “Tetanus”
- Centers for Disease Control and Prevention: “Tetanus”
- MedlinePlus: “Cellulitis”