Primary prevention of asthma in children

Many modifiable and non-modifiable factors have been associated with increased or decreased risk of asthma development in children.

Although many factors have been associated with increased asthma risk in observational studies, and available data suggest a causal association for some, none have been definitively shown to cause asthma directly. Avoidance or correction of these risk factors has not been shown to prevent asthma developing.

No interventions have definitively been shown to prevent asthma in children.

Advise pregnant women against smoking or exposure to environmental tobacco smoke.

Advise pregnant women and women planning pregnancy to follow current national guidelines for Vitamin D supplementation.

Do not recommend dietary restrictions during pregnancy for the purpose of preventing asthma in children.

Follow guidance from the Australasian Society of Clinical Immunology and Allergy.

Do not recommend dietary restrictions for breastfeeding women to prevent asthma in their children.

Advise parents/carers to ensure babies and children are not exposed to cigarette smoke.

Pregnant women should be warned not to smoke, and families should be warned not to smoke when they are with babies or children, or in rooms or cars that are used by them.

Systematic reviews of clinical trials of food allergen avoidance during pregnancy have found no overall reduction in rates of asthma or atopic dermatitis (eczema) in infants.[Kramer 2012, Netting 2014] A 2012 Cochrane review concluded that prescription of antigen-avoidance diets during pregnancy was unlikely to reduce substantially the risk of asthma or allergies in children with a family history of allergies.[Kramer 2012] Restriction diets during pregnancy could also compromise maternal or foetal nutrition.[Kramer 2012]

The Australasian Society of Clinical Immunology and Allergy recommends that pregnant and breastfeeding women maintain a healthy balanced diet, rich in fibre, vegetables and fruit, recommends that up to 3 serves of oily fish per week during pregnancy and breastfeeding may help prevent eczema in children, and recommends against maternal dietary exclusions for allergy prevention.[ASCIA 2020]

Randomised clinical trials of prenatal fish oil supplementation to prevent allergic disease have reported inconsistent results. A clinical trial comparing prenatal supplementation with fish oil (2.7 g of long-chain omega 3 polyunsaturated fatty acids) versus placebo (olive oil) or no intervention reported a significant reduction in the risk of asthma (measured as prescription of asthma medication) at up to age 18–19 years in the fish oil group, compared with the olive oil group, but no difference between groups in lung function or allergic sensitisation at age 18–19 years.[Hansen 2017] In another randomised clinical trial, prenatal supplementation with 2.4 g fish oil per day was associated with a reduction in the rate of wheeze or asthma in children at 3-year follow-up.[Bisgaard 2016] However, in a study in pregnant women with family history of allergic disease, supplementation with fish oil capsules (800 mg/d docosahexaenoic acid [DHA] and 100mg/d eicosapentaenoic acid [EPA]) had no effect on asthma at 3 or 6 years’ follow-up, compared with placebo (vegetable oil capsules).[Best 2018, Best 2016, Palmer 2013]

Systematic reviews of clinical trials evaluating prenatal long-chain omega-3 polyunsaturated fatty acid supplementation for allergy prevention found that supplementation had no effect on asthma or wheeze in children.[Best 2016, Gunaratne 2015] ‘Fish oil’ is not well defined and the optimal dosing regimen has not been established.[GINA 2025]

Probiotic supplementation during pregnancy has not been shown to reduce rates of wheezing or asthma in children.[Zuccotti, Azad 2013, Elazab 2014]

Clinical trials of vitamin D supplementation during pregnancy suggest a protective effect against wheezing and asthma in early childhood.[Wolsk 2017, Vahdaninia 2017] Earlier supplementation may be more effective in reducing the risk of asthma than late supplementation[Shadid 2023] and maintenance 25(OH) vitamin D levels of at least 30 ng/mL (75 nmol/L) may be important.[Wolsk 2017] One clinical trial reported that vitamin D supplementation (4400 IU/d) during pregnancy significantly reduced the rate of asthma in offspring at ages 3 and 6 years, compared with standard prenatal multivitamin with vitamin D (400 IU/d).[Weiss 2024] 

However, the Royal Australian and New Zealand College of Obstetricians and Gynaecologists recommends that all pregnant women take 400 IU vitamin D per day as part of a multivitamin supplement, and recommends against routine vitamin D level testing.[RANZCOG 2019]

Higher diversity of food during the first year of life has been associated with lower risk of developing asthma.[Lis-Swiety 2016]

The Australasian Society of Clinical Immunology and Allergy does not provide specific guidance on prevention of allergic asthma, but advice on allergy prevention includes introduction of solid foods at around age 6 months (not before 4 months), and introduction of common food allergens before age 12 months unless the child is already known to be allergic to a food.[ASCIA 2020]

A systematic review of clinical trials evaluating infant supplements found that polyunsaturated fatty acids given as supplements or added to infant formula did not affect rates of asthma at up to age 2 years or at age 2–5 years.[Schindler 2016]

Perinatal supplementation with oral prebiotics and probiotics has not been shown to reduce the risk of childhood asthma.[von Mutius 2020]

The effects of oral bacterial lysates in infancy on later risk of wheezing is under investigation.[University of Arizona 2024]

The Australasian Society of Clinical Immunology and Allergy recommends against hydrolysed infant formula (partial and extensive) for the prevention of allergic disease.[ASCIA 2020]

There is no conclusive evidence that breastfeeding protects against development of asthma.[von Mutius 2020]

The Australasian Society of Clinical Immunology and Allergy recommends breastfeeding for at least 6 months, for its general benefits, with a standard cow’s milk based formula if breastfeeding is not possible.[ASCIA 2020] It advises against cow’s milk, goat’s milk (or milk other mammals), soy milk, nut milk of cereal milk as the main source of milk before age 12 months.[ASCIA 2020]

Despite a positive association between early life exposure to aeroallergens, or sensitisation to aeroallergens, and the development of asthma,[Gaffin 2014, Arshad 2010, von Mutius 2020] allergen avoidance measures in homes have not been established as effective and feasible strategies for preventing asthma in children.

Single allergen reduction strategies, such as the use of mattress covers that are impermeable to house dust mite, are not effective in preventing the development of wheezing or asthma in children.[Arroyave 2014, Maas 2009] An Australian controlled clinical trial that compared house dust mite avoidance (acaricide and impermeable mattress covers), from birth to 5 years, with simple advice on cleaning, vacuuming, dusting and maintaining adequate ventilation,[Peat 2004, Marks 2006] reported no reduction in the risk of developing asthma at age 11.5 years.[Toelle 2013] Multimodal allergen avoidance strategies may reduce the risk of asthma in children.[Arshad 2003, Becker 2004, Schonberger 2005, Chan-Yeung 2005, van Schayck 2007, Maas 2009, Scott 2012] However, these strategies require intensive effort and may not be feasible for many families.

Specific-allergen immunotherapy for children with grass pollen allergic rhinitis or house dust mite allergic rhinitis has not been definitively shown to prevent the development of asthma, but evidence from clinical trials of at least 3 years’ treatment suggest a possible reduction in new diagnoses.[Arshad 2022, Farraia 2022]

RSV infection in infancy is associated with increased risk of developing asthma.[Rosas-Salazar 2023, Martinez 2019]

Prophylaxis with palivizumab (humanised IgG₁ monoclonal antibody directed against RSV) in infants has not been shown to reduce the risk of physician-diagnosed asthma or lung function at 6 years.[Scheltema 2018]

RSV vaccination of pregnant women[Kampmann 2023] and healthy infants[Hammitt 2022] reduces RSV infection requiring medical treatment in the first year of life. It has not yet been established whether RSV prenatal vaccination will prevent development of recurrent wheeze or asthma in children.[GINA 2025] 

The Australian Technical Advisory Group on Immunisation recommends RSV vaccination for pregnant women. RSV vaccination for eligible pregnant women is funded under for National Immunisation Program.[Australian Government 2025]

The Australian Technical Advisory Group on Immunisation recommends passive immunisation with monoclonal antibody against RSV (nirsevimab) for neonates and infants younger than 8 months whose mothers were not vaccinated at least 2 weeks before delivery or who are at increased risk of severe disease.[Australian Government 2025]

Early-life microbial exposure appears to be important for activation of the innate immune system and the development of regulatory immune responses, and may contribute to protection against asthma and allergy.[Smits 2016]

Living on traditional European or Amish farms has consistently been associated with reduced risk of developing wheeze in pre-school children or asthma in school-aged children.[von Mutius 2016] This association is thought to be due to exposure high concentrations of allergens, other plant and animal materials, bacteria, fungi, and other microbes.[von Mutius 2016]

Living with pets during early childhood is associated with reduced risk of developing asthma.[Indolfi 2023]

Overall, dietary intake of fruits and vegetables, and a range of vitamins, has been associated with lower rates of asthma or wheeze in systematic reviews of observational studies (mainly cross-sectional studies).[Garcia-Larsen 2016, Hosseini 2017, Seyedrezazadeh 2014] The ‘Mediterranean diet’ (high in fruits and vegetables, whole grains, oily fish and olive oil, and low in red meat) has been associated with lower rate of asthma or wheeze in systematic review of observational studies.[Garcia-Larsen 2016]

High fish oil intake (both fish consumption and supplementation with long-chain omega-3 polyunsaturated fatty acids) has been associated with reduced asthma risk reduced in children. A systematic review of prospective observational studies and RCTs found that asthma risk was reduced by high fish oil intake in children, including both fish consumption and long-chain omega-3 polyunsaturated fatty acids intake.[Yang 2013] Most studies were designed to measure other allergic outcomes (e.g. atopic dermatitis) and were not powered to detect effects on asthma risk.

Dietary levels of vitamins C, D, and E  in childhood are associated with lower rate of asthma or wheeze.[Garcia-Larsen 2016]

Many modifiable and non-modifiable factors have been associated with increased or decreased risk of asthma development in children.

A child’s risk of developing asthma is increased if a parent has a history of asthma; approximately 3 times higher for mothers and 2.4 times higher for fathers.[Castro-Rodriguez 2016]

Systematic reviews and meta-analyses of data from observational studies show an association between Caesarean section and a small increase in the child’s risk of developing asthma, compared with vaginal delivery.[Lis-Swiety 2016, Huang 2015] The mechanism is thought to be due to effects of altered intestinal bacterial flora on the infant’s developing immune system.[Lis-Swiety 2016, Huang 2015]

Prematurity and low birth weight are associated with increased risk of developing asthma, but this finding may not reflect direct causation.[von Mutius 2020] 

Exposure to tobacco smoke toxins in utero or in infancy is associated with increased risk of wheezing and asthma in children.[Burke 2012]

Maternal smoking during pregnancy is associated with an almost twofold increase in asthma in infants aged 2 years or younger.[Burke 2012]

Exposure to environmental tobacco smoke during pregnancy is an independent risk factor for wheeze in children up to the age of 2 years.[Vardavas 2016] In children, exposure to environmental tobacco smoke is associated with an increase in childhood asthma, but the association is weaker than for wheezing.[Tinuoye 2013]

Evidence from an Australian cohort study suggests that children with asthma whose mothers smoked during pregnancy benefit less from treatment with inhaled corticosteroids, and show less improvement in airway hyperresponsiveness over time, than those with asthma but no intrauterine exposure to smoke.[Cohen 2012]

Early-life viral lower respiratory tract infection with respiratory syncytial virus (RSV) or rhinovirus, both of which cause bronchiolitis in infants, is strongly associated with recurrent wheeze and allergic asthma in childhood.[Rosas-Salazar 2023, Martinez 2019] Estimates of attributable risk of asthma due to RSV are 13–22% among children aged 5 years and under, 11–27% among children aged 5–11 years, and 32% among children 12 years and over.[Szabo 2013]

Parental and household smoking has been associated with increased risk of bronchiolitis in infancy.[Jones 2011]

Several studies have reported an association between prenatal or early-life exposure to antibiotics and increased risk of childhood asthma.[Baron 2020]

Prenatal and childhood paracetamol use has been associated with increased asthma risk in several observational studies. However, causality has not been demonstrated. 

Meta-analyses of observational studies (mainly prospective cohorts) show that paracetamol use during pregnancy is associated with increases in the risk of wheeze in early childhood and of childhood asthma at age 5 or older.[Castro-Rodriguez 2016, Cheelo 2015, Dick 2014, Eyers 2011, Etminan 2009] However, this finding must be interpreted with caution because of heterogeneity among studies and the fact that some studies did not control for maternal respiratory tract infections.

Several systematic reviews have reported an association between paracetamol use in infancy and development of asthma.[Dick 2014, Etminan 2009, Heintze 2013] However, many of the included studies were of low quality and the association may be due to confounding by indication. A meta-analysis of observational studies found that increasing frequency of use of paracetamol during infancy was associated with a small increase in the risk of childhood asthma, but the effect was reduced to very small after adjusting for respiratory tract infections.[Cheelo 2015] A 2016 systematic review of systematic reviews (overview) concluded that there was no significant association between paracetamol use during infancy and childhood asthma, after adjustment for lower respiratory tract infections.[Castro-Rodriguez 2016]

There is epidemiological evidence for an association between low vitamin D in pregnancy and development of asthma during the first 10 years of life.[Lis-Swiety 2016] A systematic review reported a U-shaped relationship between maternal blood 25-hydroxyvitamin D levels and risk of childhood asthma, with the lowest risk at approximately 70 nmol/L.[Song 2017]

Low maternal vitamin E intake during pregnancy is associated with increased risk of asthma in offspring up to age 10 years.[Lis-Swiety 2016]

High intake of fast foods by children has been associated with increased risk of developing asthma in observational studies.[Hijazi 2000, Wickens 2005, Carey 1996, Huang 2001]

Maternal obesity during pregnancy increases the risk of asthma or wheeze in children, based on a meta-analysis of observational studies.[Forno 2014]

High gestational weight gain was also associated with higher risk of asthma or wheeze.[Forno 2014]

Childhood overweight or obesity have been associated with increased risk of developing asthma or wheeze.[Deng 2019]

Population-based studies have observed a positive association between early life exposure to aeroallergens (e.g. house dust mite, indoor mould) or sensitisation to aeroallergens and the development of asthma,[Gaffin 2014, Arshad 2010, von Mutius 2020] Allergic rhinitis is a major risk factor for asthma and often precedes it.[Pawankar 2009, Burgess 2007, Shaaban 2008] These associations probably reflect the common allergic causes of both conditions, rather than a causal link.[Shaaban 2008]

Observational studies show an association between pollution and asthma risk in children. However, it is difficult to control for the influence of confounding factors such as socioeconomic status. Systematic reviews and meta-analyses have reported that prenatal exposure to air pollution (including nitrogen dioxide, particulate matter) was associated with increased risk of wheezing and asthma in children,[Hehua 2017] early-life exposure to air pollution (nitrogen dioxide, ozone, volatile organic compounds, and particulate matter) was associated with increased risk of allergic asthma in children,[Gaffin 2017] and childhood exposure to traffic pollution (including soot from vehicle emissions, nitrogen dioxide, fine particulate matter, carbon monoxide and particulate matter) was associated with increased risk of asthma.[Khreis 2017, Gasana 2012]

Epidemiological studies have consistently reported an association between early life exposure to indoor dampness and mould (particularly visible mould and mould odour) and increased risk of developing asthma or wheeze.[Quansah 2012, Mendell 2011, Tischer 2011, Tischer 2011] However, it is difficult to control for the influence of confounding factors such as socioeconomic status.

Exposure to fumes from polyvinyl chloride products (PVC) surface materials is associated with increased risk of asthma in children, while exposure to heated PVC fumes (mainly in the workplace) is associated with increased risk of asthma in adults.[Jaakkola 2008]

The use of gas stoves or ovens in the home has also been associated with development of asthma in children.[Lanphear 2001]