Incubation Period

What is an incubation period?

“Incubation period” is a medical term that refers to the time between exposure to an infectious disease and the start of symptoms.

You can get infected in a variety of ways, depending on the specific disease and how it spreads. For example, exposure might mean you:

• Touched a contaminated surface and then touched your mouth.
• Breathed in droplets from someone’s cough or sneeze.
• Had sexual contact with someone who has a sexually transmitted infection (STI).
• Ate undercooked meat or raw milk.
• Came in contact with an animal or insect carrying an infectious disease.

You can sometimes pinpoint the moment you were exposed to germs. Maybe it was that long train ride where the person next to you kept coughing. Or perhaps it was the dinner with your cousin who tested positive for COVID-19 the next day. Other times, you have no clue you were exposed to germs until you wake up feeling sick. Then, you try to think back to where it all began.

Knowing the incubation period for common diseases can help you know how long you should be on the lookout for symptoms — in yourself or a loved one — and when you’re out of the woods.

What happens during the incubation period?

During the incubation period, germs take up residence in your body and start making copies of themselves (reproducing). Soon, your immune system takes notice and jumps into action to clear out the invaders. This immune response leads to inflammation and symptoms like a sore throat, runny nose, rash or diarrhea.

How long might an incubation period be?

Healthcare providers usually measure an incubation period in days or weeks. But sometimes, like with certain STIs, an incubation period can span a month or more. Certain foodborne illnesses can cause symptoms within just hours.

Incubation period for common infectious diseases

Below are typical incubation periods for infectious diseases you or your family might encounter.

• Adenovirus: Usually five to six days but can be two to 14 days.
• Chickenpox: 10 to 21 days (average 14 to 16 days).
• Common cold: 12 hours to three days.
• COVID-19: Two to 14 days (average of three to four days for omicron and its subvariants).
• Hand, foot and mouth disease: Three to six days.
• Influenza (flu): One to four days.
• Measles: Usually eight to 12 days but can be up to 21 days.
• Mono (mononucleosis or glandular fever): Four to six weeks.
• Pink eye (bacterial): 24 to 72 hours
• Pink eye (viral): 12 hours to 12 days.
• Rubella: 12 to 23 days (average of 14 days).
• RSV: Four to six days
• Strep throat: Two to five days.
• Tetanus: Three to 21 days.
• Walking (atypical) pneumonia: Two to four weeks.

Incubation period for sexually transmitted diseases

Learning your partner tested positive for an STI can make you worry if you’ll test positive, too. The first thing to do if you’ve been exposed to an STI — even if you don’t have symptoms — is to call a healthcare provider. They’ll ask you some questions to help figure out your risk of catching the infection. They’ll also advise you on what to do next — like coming in for STI testing or treatment.

The incubation periods for STIs can vary widely. Here are some examples:

• Chlamydia: Seven to 21 days.
• Genital warts: 14 days to eight months.
• Gonorrhea: One to 14 days.
• Herpes simplex 2 (genital herpes): Two to 12 days but can be months or even years.
• HIV (acute HIV infection): Two to four weeks.
• Syphilis: 10 to 90 days (average of 21 days).

It’s possible to have an STI and not have any symptoms. Simply getting past the incubation period isn’t enough to assume all is OK. That’s why it’s important to talk to a provider about any exposures so you can get tested and know for sure.

Stomach bug incubation period

The incubation period for a stomach bug (commonly called the stomach flu, gastric flu or food poisoning) depends on the specific “bug” that’s making you sick. Many different viruses, bacteria and parasites can cause gastroenteritis, or inflammation in your stomach and intestines. This inflammation causes telltale stomach bug symptoms like nausea, vomiting and diarrhea.

Here are some incubation periods to be aware of:

• Campylobacter infection: Usually two to four days but can be one to 10 days.
• E. coli infection (affecting your digestive system): Eight hours to 10 days, depending on the strain.
• Giardiasis (acute): One to 14 days (average of seven days).
• Norovirus: 12 to 48 hours.
• Rotavirus: One to two days.
• Salmonella infection: Usually 12 hours to four days but can be seven days or longer.

Learning the incubation period for different stomach bugs is useful because you can pinpoint or rule out certain causes — like that sandwich that tasted a little funky or those leftovers you took a chance on.

You typically get a stomach bug from consuming contaminated food or water. But you can also get it from close contact with someone who’s sick or from touching a contaminated surface and then touching your mouth or nose.

Are you contagious during the incubation period?

Often, the answer is yes. The incubation period and the infectious period commonly overlap. In other words, you can often spread germs before you even have symptoms.

The infectious period is the span of time when you can spread germs to others that might make them sick. This usually refers to the days when you have symptoms but also at least some of the days leading up to your first symptoms.

For example, you’re most likely to spread the flu (influenza) to others during the first three days of symptoms. But it’s possible to spread it one day before your symptoms begin. That means the incubation period and the infectious period can overlap by about a day.

If you know you were exposed to an infectious disease but feel fine — and you’re wondering if you could make others sick — call a healthcare provider. They can tell you more specifics about the disease in question, its incubation period and how likely it is that you can spread the disease to others.

Why is the incubation period important?

Knowing the incubation period for specific diseases can:

• Help you trace where and when you or your child picked up germs.
• Help you know how long you should stay away from others (quarantine) or take precautions — like wearing a mask — to avoid spreading germs. Many common infections, like the flu and COVID-19, can spread from you to others before you have any symptoms.
• Give you the chance to talk to a healthcare provider about whether you should get treatment after exposure to certain diseases, like STIs, to prevent an infection and/or avoid spreading it.

But there’s a catch — incubation periods are estimates drawn from research. They’re credible and accurate, but there are always outliers. That means some people might get sick sooner or later than expected after an exposure. Factors like your age or the amount of germs you were exposed to might play a role in how slow or fast you develop symptoms.

That’s why talking to your healthcare provider is the best way to know your risk of coming down with an infection. They’ll tell you if you should be concerned, what precautions you should take and whether you need to do anything (like get medications or a vaccine) due to your exposure.