Thumb sucking and nail-biting early in life may reduce allergies later in life.
Linus’ thumb-sucking habit just might reduce his risk of common allergies. An article in Pediatrics found that kids who had their fingers in their mouths at ages 5, 7, 9, and 11 years old were less likely to have a reaction to a skin prick test for allergies later in life (ages 13 and 32 years) . Study participants were pricked with common allergens including: house dust mites, grass, cat, dog, horse, wool, and several fungi at ages 13 and 32. Redness and swelling of the skin indicated a sensitivity to the allergen. Kids who were both thumb-suckers and nail-biters were least likely to react to the skin test, though thumb-sucking only seemed to have a stronger effect than nail-biting alone. Sucking or biting on their fingers seemed to lower kid’s allergy levels, even after considering whether or not the parents had allergies or smoked, the number of people and pets in the house, breastfeeding, and socioeconomic status. Thumb-sucking and nail biting had no effect on asthma or hay fever, perhaps because these were self-reported whereas the skin prick test is more definitive.
Are fingers early “allergy injections”?
Why might spending your childhood with your fingers in your mouth reduce the chance of allergies? Maybe exposure early in life makes a person less sensitive. A type of environmental microbe “vaccination” or “allergy shot”. Early, low dose exposures to fungi, bacteria, dust mites, pollen, and animal dander may train a child’s immune system that these items are not harmful. This “fingers in mouth” study joins several others suggesting that exposure to “dirt” might reduce the chance of allergies in later life. Children who grow up on farms or with pets  and children whose parents sucked their pacifiers “clean”  have reduced instances of allergies. If that is the case, I certainly wish that I’d spent more of my childhood with my fingers in my mouth instead of doing a series of allergy shots after moving to different parts of the U.S. as an adult.
What about breastfeeding and allergies?
This ~40 year study followed over 1, 000 people in New Zealand from birth is yet another example of the powerful findings of such “cohort population studies”. Collecting a wide variety of detailed data on such a large group of individuals in one country allows for differences in people’s lifestyles, environment, and sometimes genetic diversity to be removed from the study. Kids who sucked their thumbs, but had parents who had allergies or smoked were still less likely to be allergic than kids who didn’t suck their thumbs. I was surprised that breastfeeding didn’t seem to have an effect on allergies since other research has seen an association [4, 5], though the findings on breastfeeding and asthma is mixed. Breastmilk’s unique sugar composition influences an infant’s gut microbiome [6-14]. The different bacteria in the gut microbiome are hypothesized to influence immune development and reduce allergies [7, 15-18]. Switching to the sugar composition of formula or even between formula and breastmilk change the gut microbiome [19-21] as does introduction to solid food and cessation of breastfeeding after solid food introduction . However, in the New Zealand cohort “breastfed” was defined as 4 weeks or longer. Is there a difference between exclusive breastfeeding and mixed feeding? Does length of time of exclusive breast feeding make a difference? Hopefully more data and future studies that take these considerations into account will give us further insight.
When I told my family about this study around the dinner table, my oldest daughter shouted “YES!” pumping her fist in the air. Four years previously, she was a nail-biter. “Mama, you MADE me stop biting my nails!” Well, honey, that’s the process of science. New data makes us re-examine our old ideas.
Share the Microbial Love
Thank you for reading my blog.
Please share this post if you enjoyed it.
If you received something of value from this post or the blog, support the blog either through a “tip” at the PayPal link below or through my affiliate links (at no cost to you).
- Lynch SJ, Sears MR, Hancox RJ: Thumb-Sucking, Nail-Biting, and Atopic Sensitization, Asthma, and Hay Fever. Pediatrics 2016.
- Johnson CC, Alford SH: Do animals on the farm and in the home reduce the risk of pediatric atopy? Curr Opin Allergy Clin Immunol 2002, 2(2):133-139.
- Hesselmar B, Sjöberg F, Saalman R, Åberg N, Adlerberth I, Wold AE: Pacifier Cleaning Practices and Risk of Allergy Development. Pediatrics 2013.
- Kull I, Wickman M, Lilja G, Nordvall SL, Pershagen G: Breast feeding and allergic diseases in infants—a prospective birth cohort study. Arch Dis Child 2002, 87(6):478-481.
- Kramer MS, Kakuma R: Optimal duration of exclusive breastfeeding. Cochrane Database of Systematic Reviews 2012(8).
- German JB, Freeman SL, Lebrilla CB, Mills DA: Human Milk Oligosaccharides: Evolution, Structures and Bioselectivity as Substrates for Intestinal Bacteria. Nestle Nutrition workshop series Paediatric programme 2008, 62:205-222.
- Jost T, Lacroix C, Braegger C, Chassard C: Impact of human milk bacteria and oligosaccharides on neonatal gut microbiota establishment and gut health; 2015.
- Underwood MA, Gaerlan S, De Leoz MLA, Dimapasoc L, Kalanetra KM, Lemay DG, German JB, Mills DA, Lebrilla CB: Human Milk Oligosaccharides in Premature Infants: Absorption, Excretion and Influence on the Intestinal Microbiota. Pediatr Res 2015.
- Underwood MA, German JB, Lebrilla CB, David A M: Bifidobacterium longum subspecies infantis: champion colonizer of the infant gut. Pediatr Res 2014.
- Wang M, Li M, Wu S, Lebrilla CB, Chapkin RS, Ivanov I, Donovan SM: Fecal microbiota composition of breast-fed infants is correlated with human milk oligosaccharides consumed. J Pediatr Gastroenterol Nutr 2015, 60(6):825-833.
- Zivkovic AM, German JB, Lebrilla CB, Mills DA: Human milk glycobiome and its impact on the infant gastrointestinal microbiota. Proceedings of the National Academy of Sciences 2011, 108(Supplement 1):4653-4658.
- Björkstén B, Sepp E, Julge K, Voor T, Mikelsaar M: Allergy development and the intestinal microflora during the first year of life. J Allergy Clin Immunol 2001, 108(4):516-520.
- Grönlund MM, Gueimonde M, Laitinen K, Kociubinski G, Grönroos T, Salminen S, Isolauri E: Maternal breast-milk and intestinal bifidobacteria guide the compositional development of the Bifidobacterium microbiota in infants at risk of allergic disease. Clinical & Experimental Allergy 2007, 37(12):1764-1772.
- Madan JC, Farzan SF, Hibberd PL, Karagas MR: Normal neonatal microbiome variation in relation to environmental factors, infection and allergy. Current opinion in pediatrics 2012, 24(6):753-759.
- Narayan N, Méndez-Lagares G, Ardeshir A, Lu D, Van Rompay KKA, Hartigan-O’Connor DJ: Persistent effects of early infant diet and associated microbiota on the juvenile immune system. Gut Microbes 2015:00-00.
- Praveen P, Jordan F, Priami C, Morine MJ: The role of breast-feeding in infant immune system: a systems perspective on the intestinal microbiome. Microbiome 2015, 3:41.
- Schwartz S, Friedberg I, Ivanov IV, Davidson LA, Goldsby JS, Dahl DB, Herman D, Wang M, Donovan SM, Chapkin RS: A metagenomic study of diet-dependent interaction between gut microbiota and host in infants reveals differences in immune response. Genome Biol 2012, 13(4):r32.
- Voreades N, Kozil A, Weir T: Diet and the development of the human intestinal microbiome. Frontiers in Microbiology 2014, 5.
- Guaraldi F, Salvatori G: Effect of Breast and Formula Feeding on Gut Microbiota Shaping in Newborns. Frontiers in Cellular and Infection Microbiology 2012, 2:94.
- Mueller NT, Bakacs E, Combellick J, Grigoryan Z, Dominguez-Bello MG: The infant microbiome development: mom matters. Trends Mol Med 2015, 21(2):109-117.
- Pop M: We are what we eat: how the diet of infants affects their gut microbiome. Genome Biol 2012, 13(4):152.
- Bäckhed F, Roswall J, Peng Y, Feng Q, Jia H, Kovatcheva-Datchary P, Li Y, Xia Y, Xie H, Zhong H et al: Dynamics and Stabilization of the Human Gut Microbiome during the First Year of Life. Cell Host & Microbe 2015, 17(5):690-703.