# How can a cold be contagious a day before you have symptoms? **URL:** \ **Category:** Factual Questions\ **Created:** [January 21, 2019, 6:46am UTC](https://boards.straightdope.com/t/how-can-a-cold-be-contagious-a-day-before-you-have-symptoms/828140 "2019-01-21T06:46:13Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![elfkin477](https://avatars.discourse-cdn.com/v4/letter/e/a9a28c/32.png) [@elfkin477](https://boards.straightdope.com/u/elfkin477)\ **Post date:** [January 21, 2019, 6:46am UTC](https://boards.straightdope.com/t/how-can-a-cold-be-contagious-a-day-before-you-have-symptoms/828140/1 "2019-01-21T06:46:13Z")
It seems like authorities agree that colds are contagious from the day before you have symptoms to several days later. But if you aren’t yet coughing, sneezing, or blowing your nose then touching things without washing your hands, how are you spreading the illness? ---
**Author:** ![UDS](https://avatars.discourse-cdn.com/v4/letter/u/ecae2f/32.png) [@UDS](https://boards.straightdope.com/u/UDS)\ **Post date:** [January 21, 2019, 6:58am UTC](https://boards.straightdope.com/t/how-can-a-cold-be-contagious-a-day-before-you-have-symptoms/828140/2 "2019-01-21T06:58:29Z")
> [@elfkin477](#): > > It seems like authorities agree that colds are contagious from the day before you have symptoms to several days later. But if you aren’t yet coughing, sneezing, or blowing your nose then touching things without washing your hands, how are you spreading the illness? By exhaling. And by touching things without washing your hands. You’re _more_ infectious once you become symptomatic, since the concentration of the virus in your exhalations goes up (peaking on about the second day on which you are symptomatic) plus you have nasal and ocular secretions. But once you’re infected, you’re infectious. ---
**Author:** ![SamuelA](https://avatars.discourse-cdn.com/v4/letter/s/c77e96/32.png) [@SamuelA](https://boards.straightdope.com/u/SamuelA)\ **Post date:** [January 21, 2019, 7:03am UTC](https://boards.straightdope.com/t/how-can-a-cold-be-contagious-a-day-before-you-have-symptoms/828140/3 "2019-01-21T07:03:24Z")
The symptoms aren’t actually _caused_ by the virus. You had it a few days before you had symptoms, the symptoms represent your immune system figuring out there’s a major problem and taking measures to deal with it. Unfortunately, they happen to help spread the virus to other people, which is a bit of a flaw. Also I’m not sure that the symptoms (fever, headache, stuff nose, sore throat) actually are _necessary_ for your body to fight off the virus. Your immune system’s B-cells should be able to fabricate an antibody to kill it without all the fuss. ---
**Author:** ![SmartAleq](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/smartaleq/32/163_2.png) [@SmartAleq](https://boards.straightdope.com/u/SmartAleq)\ **Post date:** [January 21, 2019, 7:25am UTC](https://boards.straightdope.com/t/how-can-a-cold-be-contagious-a-day-before-you-have-symptoms/828140/4 "2019-01-21T07:25:43Z")
This is why those christless anti-vaxxers ae such a hazard–up here in Vancouver WA we’re having an outbreak of measles due to these unvaxxed little plaguedogs going everywhere, including a Blazers game (potential exposure of almost 20K people), IKEAs babysitting area, the freaking airport and about every emergency room and urgent care in miles radius–and churches, of course. And Costco. See, the fun part about measles is that carriers are infectious AF for four days before they become symptomatic and the measles virus is carried airborne and is viable in the air for up to two hours after someone sneezed or snorted it out. Once the virus gets established in a body it starts replicating itself like mad and shedding itself as fast as it can–by the time you start feeling punky you’ve already exposed the gods know how many people to your virus load. This is why kids need vaxxed and everyone should get their flu shot every year. ---
**Author:** ![Hermitian](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hermitian/32/470_2.png) [@Hermitian](https://boards.straightdope.com/u/Hermitian)\ **Post date:** [January 22, 2019, 2:42pm UTC](https://boards.straightdope.com/t/how-can-a-cold-be-contagious-a-day-before-you-have-symptoms/828140/5 "2019-01-22T14:42:19Z")
> [@elfkin477](#): > > It seems like authorities agree that colds are contagious from the day before you have symptoms to several days later. What does “several days later” mean? Several days after the symptoms appear or several days after symptoms cease? ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [January 22, 2019, 10:03pm UTC](https://boards.straightdope.com/t/how-can-a-cold-be-contagious-a-day-before-you-have-symptoms/828140/6 "2019-01-22T22:03:49Z")
Just think of there being a time lag between when you _have_ a cold and when you _know_ you have a cold. This lag is one of a jillion things that gives a leg up to viruses to help them spread. Who’s the comedian who had a line about if there wasn’t a lag cavemen would have figured out to kill the guy who’s coughing or some such?