SPECIAL TOPICS IN OTORHINOLARYNGOLOGY: OTOLARYNGIC ALLERGY (E TOSKALA, SECTION EDITOR)
Hygiene Hypothesis: What Is the Current Thinking?
Nuray Bayar Muluk
Published online: 27 July 2017
Springer Science+Business Media, LLC 2017
Purpose of Review Our aim was to discuss the hygiene hy-
pothesis and current thinking about it.
Recent Findings Hygiene hypothesis suggests that an under-
lying reason for the recent prominent rise in allergic diseases
may be linked with the diminution of the incidence of early
childhood infections, which can be transmitted by means of
contact with older siblings. Hygiene hypothesis suggests that
contact with microbes in the environment in early life through
pets, unpasteurized food, and nonsterilized water may protect
from atopic diseases. Exposure to microbial pathogens and
animals in infancy prevents atopy by Th
-like cytokine re-
sponses or by modifying Th
-like immune responses.
Chronic infection and inflammation may protect against atop-
ic disease. Alteration of exposure to microorganisms and ac-
cess to clean water as well as issues related with food, sanita-
tion, medical and obstetric practices, and urban lifestyle may
have significant roles. Decreased exposure to bacteria in the
early infancy period may shift the immune system to a pre-
state which is detected in atopic cases.
Environmental exposure may lead to epigenetic changes which
causes a shift of immune reactions against microorganisms.
Summary The hygiene hypothesis implies that modern living
conditions can be responsible for the rise in the incidences of
allergic disease and asthma. Protective effect of food-borne mi-
crobes on allergic diseases is another remarkable issue.
Keywords Hygiene hypothesis
While infectious disease and hygiene have been key public
health issues for centuries , allergic diseases have only rel-
atively recently been regarded as a significant health burden.
The marked increase in the prevalence of allergic disorders,
like eczema , allergic rhinitis, and food allergy , has been
a prominent trend over the past century in all regions of the
world, but most characterized in Western countries [4, 5••].
Humans are ecosystems that host microbes, namely the
human microbiome, and these microorganisms are necessary
for maintenance of our health .Theimmunesystemfunc-
tions as a learning device, and it is similar to a computer that
has sufficient hardware and software but has only scarce data.
This lack of data must be compensated in the initial few years
of life, by means of contact with microorganisms in the envi-
ronment. In case this contact fails to provide this contiguity,
the development of immune regulatory mechanisms may fail.
Consequently, the immune system is not only responsible for
elimination of harmful organisms that are responsible for in-
fections but also may prevent the reactions triggered by agents
responsible for allergic disorders [5••].
The optimal composition of the microbiota is maintained by
diet , which needs to be diverse, and contains fiber (polysac-
charides digested by the microbiota rather than the human host)
 and polyphenols found in plant products [9–11]. A diet
This article is part of the Topical Collection on Special Topics In
Otorhinolaryngology: Otolaryngic Allergy
* Cemal Cingi
Nuray Bayar Muluk
Medical Faculty, Department of Otorhinolaryngology, Eskisehir
Osmangazi University, Eskisehir, Turkey
Medical Faculty, Department of Otorhinolaryngology, Kirikkale
University, Kirikkale, Turkey
Curr Otorhinolaryngol Rep (2017) 5:175–180