The latest theory on why a generation of allergy sufferers have been born, is the Modified Hygiene Hypothesis, whereby during early childhood, the quality of the germs in your bowel will impact on your immune system and either cause an allergic predisposition to be switched on or off. Infants born by normal vaginal delivery, have their bowel colonised by “good” lactobacilli and bifidobacteria as they pass through the birth canal and are less likely to develop eczema and asthma.  This “innoculation” will be missed if you are born by Caesarian section, and the natural bowel colonisation with these germs does not occur instead is colonised by poor quality Clostridium and Staphylococcal bowel germs which as a consequence promote the TH2 allergic prone immune reactivity. However,  Probiotic supplements during pregnancy and early childhood will compensate, as will exclusive breastfeeding also help normalise and correct bowel bacteria quality  in the newborn.  Natural sunlight and vitamin D tend to switch off allergies, and early exposure to animal bacteria also help switch off allergy development. Single children, living in a sterile indoor environment with no snotty germ-infested siblings, and living in an animal-free environment, also born by Caesarian section are at greater risk for developing allergies. Its all about having good quality germs in your childs bowel at birth and early childhood that impacts on the immune system and translates into a tendency not to develop allergies (the allergy phenotype).

Reference: Kukkonen AK, Kuitunen M. Infantile wheeze and maternal gut microbes – is there a connection? Clinical & Experimental Allergy 2012 (42) 814-816