Every time our children spend time with a group of other kids, there's at least one with the sniffles or worse. It's tempting to shield them from such sources of infection, but (leaving aside the non-medical downsides of isolation) presumably they'd grow up with weak immune systems if they didn't have this early exposure.

Does frequent exposure to sick kids, such as in daycare or public school, have a negative impact on a child's later immune health? Positive? What about very minimal exposure? Is there a happy medium to which we should strive?

I'm specifically interested in exposure to other children, not so much to environmental sources (i.e., eating dirt).

Here's an article saying that yes, some exposure to infection is probably helpful: https://www.parentmap.com/article/is-getting-sick-good-for-preschoolers It references a study, but does not link it, and my Google-fu fails me.

Another article, suggesting that there is such an effect but perhaps only for babies and toddlers: www.cnn.com/2010/HEALTH/12/06/daycare.kids/ Also, this simply claims that children will be more resistant in elementary school if they're exposed in daycare; I'm more interested in the kids' eventual health as adults.

  • 2
    A friend's favorite saying is "every cold they catch as children is a case of pneumonia they avoid as an adult" -- once you catch a particular strain of cold, you won't get it again (the same immunity process as vaccinations). Unfortunately, there are thousands of strains of cold virus. In general, therefore, the effect is positive (they're immune to more things), but I don't have good documentation for that and therefore don't want to post an Answer :)
    – Acire
    Mar 19, 2015 at 1:10
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    I don't have any official links on the subject but I'll tell you I grew up in a house that could probably have been declared a bio hazard wasteland and I pretty much never get sick. I wouldn't let them walk into a room filled with rampant disease or anything, but fearing the general sniffles is probably not a good idea. On the rare occasions my kids get sick they don't really complain much. For all I know the body of the child expects to run hot some times.
    – Kai Qing
    Mar 19, 2015 at 1:12
  • Interestingly, the health officials used to say "don't eat peanuts when pregnant" and "don't give your children peanuts, it'll give them allergies". Now they're saying the opposite, which makes far more sense. The body has to learn how to fight bacteria, and to learn how to fight it, it must encounter it. Once upon a time, humans couldn't consume cow milk, but because man kept trying, man eventually developed enough tolerance to be able to consume it. The entire pseudoscience of homeopathy is founded on similar beliefs.
    – Pharap
    Mar 19, 2015 at 11:16
  • @Pharap You're making a bit of an overgeneralization there; both theories (early peanuts lead to allergy, and early peanuts lead to non-allergy) have strong backing in science, and are both still very possible (or, more likely, some of each). Some of the preference to avoid major allergens like peanuts and shellfish is not related to avoiding becoming allergic ever, but due to how these allergies work, if you are allergic, the first time or two that you have the allergen you have a mild reaction that a one year old wouldn't necessarily be able to communicate to the parent).
    – Joe
    Mar 20, 2015 at 14:52
  • While if you have peanuts for the first time at 2 or 3, you can more likely communicate that first or second mild reaction, such that the allergy can be identified before the child has a life-threatening reaction.
    – Joe
    Mar 20, 2015 at 14:53

2 Answers 2


This is the 2010 paper discussed in the CNN article:

Côté SM, Petitclerc A, Raynault M, et al. Short- and Long-term Risk of Infections as a Function of Group Child Care Attendance: An 8-Year Population-Based Study. Arch Pediatr Adolesc Med. 2010;164(12):1132-1137. doi:10.1001/archpediatrics.2010.216.

Children contract infections around the time they initiate large structured group activities. Participation in large GCC before 2½ years old, although associated with increased infections at that time, seems to protect against infections during the elementary school years.

I found another article: Day care in relation to respiratory-tract and gastrointestinal infections in a German birth cohort study, Acta Paediatrica, 2007

Results: ... Children attending a day care centre were more likely to have common cold, bronchitis, pneumonia, otitis media and diarrhea within the first 2–3 years of life. With the exception of common cold, from year 4 onwards these associations were not statistically significant anymore and even reversed for some of the infections.

It looks like this is the 2002 paper mentioned in the ParentMap article you found:

Ball TM, Holberg CJ, Aldous MB, Martinez FD, Wright AL. Influence of Attendance at Day Care on the Common Cold From Birth Through 13 Years of Age. Arch Pediatr Adolesc Med. 2002;156(2):121-126. doi:10.1001/archpedi.156.2.121.

Attendance at large day care was associated with more common colds during the preschool years. However, it was found to protect against the common cold during the early school years, presumably through acquired immunity. This protection waned by 13 years of age.

Note that last sentence (protection waned by 13 years of age) which was not mentioned in the ParentMap article.

In each case, the study did not track children once they reached adulthood. (Presumably this is because the authors are pediatricians, and/or publishing in pediatric medical journals.) I glanced a number of articles that cited the above studies (thanks, Google Scholar!) but wasn't really able to find anything that discussed long-term impacts on adult immune systems.

  • That waning bit is extremely important! So there seems to be a degree of immunity, but temporary. With that in mind, I might prefer "X days of sick six-year-old" over "X days of sick two-year-old." Hmm. Thank you for digging these up!
    – user3034
    Mar 19, 2015 at 20:30
  • I don't think they meant waning as in "the older kids start getting sicker" but rather the sick days even out.
    – Acire
    Mar 19, 2015 at 21:02
  • Right. I'm saying that an older child can generally cope a little better than a younger, if the net result is simply (e.g.) six days with the flu at age two vs six days with the flu at age six. Older kids are less likely to spit cough syrup in your hair.
    – user3034
    Mar 19, 2015 at 21:38
  • OK just making sure ^.^
    – Acire
    Mar 19, 2015 at 22:13
  • 1
    +1 - great answer. I don't have the time to answer as well, but yes, the benefit flows over into adulthood as well. In late adulthood (i.e. elderly), everyone's immunity starts to wan, regardless. Mar 20, 2015 at 16:49

There are a few things at work here, that seem to be combined in your question.

The first is the concept that your child should be exposed to diseases at a younger age in order to avoid sickness at an older age. Much of your immune system works such that once you are exposed to a particular antigen (such as a protein from a virus or a bacteria), you produce T-cells and other related cells that protect against that antigen, and some of them persist for a long time - decades or even your entire life. This is how and why immunization works; it works the same way by simply getting sick. Here's a somewhat detailed explanation of memory in the immune system.

Chicken pox is the classic example of this from my generation; you knew you would get sick once from it, so your parents often tried to get you sick with chicken pox at 3 or 4, so you wouldn't have it at 7 or 8 - or even older, as an adult when it can be potentially more dangerous.

What is happening here is that everyone has a set of diseases that is in the local environment; this includes bacteria in your water, parasites, viruses, and bacteria in the dirt, and the various respiratory and skin-carried bacteria, viruses, etc., that the people in your community carry. You get exposed to these diseases as a child, have a reaction once or a couple of times, and then have sufficient immunity to be protected. Having your children in daycare means they get these reactions early in childhood rather than later. Other diseases - measles, the flu, chickenpox, etc. - tend to not work quite the same way (in the sense that you're not likely to be exposed to them just by going to daycare, though you certainly could be; and some of them, like the flu, are less easy to gain effective immunity from).

There is some evidence of this; this LiveScience article discusses a recent study that confirms that kids get sick the same overall, but get it earlier, when in daycare. This is intuitively logical; for diseases that you can be effectively protected from, you will tend to get them at one time or the other, with a comparatively similar cumulative amount. Diseases like influenza, which are harder to gain total immunity from, may not follow this pattern, but apparently either are insignificant in the total cumulative sample or you do gain some protection from (perhaps reduction in duration).

The second concept is the Hygeine Hypothesis, which refers to the concept that being "too clean" leads to more susceptibility to allergies and allergic diseases later in life. There is less support for this being related to common childhood diseases (although that support may be hard to obtain in any event, given the prevalence of immunizations); it's also thought to be most important very early in life (as a fetus, or in the first few months of life), and many things point to parasites as being more useful than viruses or bacteria here.

There is fairly significant support for this hypothesis, although it is certainly far from proven, both in its mechanism and the overall causal relationship. The hypothesis is only a few decades old (Wikipedia dates it to 1989, which my wife (an immunologist) thought was about right), so it still has some time to go before it's widely accepted as theory (both from needing more data, and more time for refutation).

The study you referred to in the OP may be either the study referenced in my first section, or the hygiene hypothesis - or it could be both, as it's entirely possible they're one and the same mechanism. The earlier study does mention asthma specifically, but it references it as if it were not part of the study ("Other studies show...").

I did find a study on The effect of cats and daycare exposure to asthma, although on a specific population of children deemed likely to get asthma (based on their having atopic dermatitis, a strong asthma risk factor). It showed a significant risk reduction for asthma for children in daycare; as with any study it's hard to say if other correlated factors could be relevant (and if the subpopulation is representative of the greater population).

The specific effects on asthma and allergies are likely to follow you through later in life, all the way through adulthood. The effects from starting daycare to avoid later sicknesses will likely be eliminated by mid-childhood (I've seen numbers around 10-13 years of age).

  • The study about having a pet in the home for less than 6 hours a day goes well with this answer of yours. Respiratory Tract Illnesses During the First Year of Life: Effect of Dog and Cat Contacts
    – user11394
    Mar 20, 2015 at 18:36
  • I'm specifically interested in exposure to other children, not so much to environmental sources (i.e., eating dirt). Is there any evidence that early exposure to infectious diseases has an impact on adult health?
    – user3034
    Mar 21, 2015 at 17:13
  • I think my answer addressed that, although perhaps I wasn't clear enough. The 'daycare germs' part appears to have no impact into adult health. The hygiene hypothesis mostly covers dirt et al and not other children, though it's not necessarily all that well studied. The link between respiratory diseases early in life and reduced asthma risk is your best bet, as asthma usually follows you into adulthood; it's not necessarily a strong link.
    – Joe
    Mar 22, 2015 at 2:23

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