The ideal outcome of pregnancy and breastfeeding would be to expose the baby to sufficient levels of allergen that would promote long-term tolerance but not allergic sensitisation.

by Dr Adrian Morris

allergy-pregPregnancy is a time of intense change within the female body.  Hormones have a profound influence on the immune system and allergic diseases may be affected by these changes. The hormones of pregnancy have  steroidal type effects and which can dampen down allergies. But while in the pregnant state, the female immune system is dampened to prevent rejection of the foetus (which is immunologically a “foreign organism”).  This state of increased immune tolerance has the spin-off of less direct vigilance against foreign substances.  However, the allergy triggering potential of the immune system may also be heightened during pregnancy with the shift to an allergy type immune response [1]. Asthma for example may become worse with frequent attacks, it may even occur for the first time in pregnancy.  But paradoxically it may become less severe and easier to control during pregnancy.

What happens to existing allergies in pregnancy

Good Asthma control is important in pregnancy to maintain an adequate oxygen supply to growing foetus. Prematurity and low birth weight may result from poor asthma control in the mother. Most asthma drugs can be safely used in pregnancy and there is no evidence that there is any increased risk to the foetus.  We do however recommend the lowest possible doses of any medication sufficient to control symptoms in the pregnant mother.

Nasal allergies often occur for the first time in pregnancy.  Pregnant mothers are prone to nasal blockage and irritating nasal symptoms and increased nasal discharge. This state of affairs seems to be triggered by the hormonal changes in pregnancy.

Urticaria and allergy-like rashes are also common in pregnancy. One particular rash that is peculiar to pregnancy is the Pruritis and Urticaria Papules and Plaques in Pregnancy ( PUPPP syndrome).  This manifests with intensely itchy eruptions, particularly on the lower abdomen and upper thighs of the pregnant person.  After the birth, the rash rapidly disappears but can be most debilitating during the last few months of pregnancy.  Eczema on the other hand often improves in pregnancy and this may possibly be due to the increase in the body’s natural steroid-like hormones that are produced during pregnancy.

Preventing allergies in the unborn infant

As far as the unborn baby’s health is concerned, the pregnancy and treatment thereof can have profound impact on the foetus’s health and predisposition to allergy.  We know that if the mother has allergies there is a 30% chance of her baby having an allergy.  If both parents have allergy, the baby’s risk increases to 60% and if both parents have the same allergy for example asthma, then the risk of allergy in the unborn baby reaches 80%.  Maternal smoking during pregnancy and the avoidance of allergy provoking foods in her diet in the last few months of pregnancy may encourage allergic diseases to develop in the baby. However the evidence is still lacking that diet in pregnancy makes any difference[3].  A hypoallergenic (low allergen) diet may also be more disadvantageous causing possible maternal and foetal malnutrition rather than advantageous for allergy prophylaxis.  American and European guidelines thus recommend a normal diet without any exclusions during pregnancy and whilst breastfeeding with the exception of adding probiotics. However if the baby does have an established allergy (cows milk, egg, peanut), then the nursing mother should avoid these foods in her diet as traces do pass into the breast milk.

The foetus is exposed to circulating maternal antigens via amniotic fluid and the placenta.  We know that unborn babies start to produce the allergy regulating IgE antibody from 20 weeks of pregnancy.  Transplacental passage of common allergens such as cow’s milk B-lactglobulin, egg ovalbumin and major birch pollen allergens occurs before 26 weeks of pregnancy [1]. We used to measure Total Cord Blood IgE levels at birth as an indicator of probable allergic diathesis, but this test is not very accurate, and is no longer recommended.

Smoking in early pregnancy is a potent trigger for the development of allergies in the unborn baby and if the baby is born into a smoking household this risk increases. The month of birth is extremely important if in spring with subsequent pollen sensitisation.  If a baby is born to allergic parents and the birth month coincides with the beginning of the pollen season, then there is an increased risk of nasal allergies and asthma. Caesarean section is a risk factor for infants developing allergies especially if mother is allergic. Vaginal birth exposes the newborn to “healthy” vaginal bacteria which stimulate the baby’s natural gut immunity and switch off allergies.  Saturated fat intake during breastfeeding is a risk factor for allergic sensitisation.  The maternal diet should thus be supplemented with plentiful Vitamin D, Omega 3 and polyunsaturated fish oils (but not fish protein).

High maternal exposure to volatile organic compounds (VOCs) found in smoke, new carpets and after recent home renovation may increase allergic diseases in their offspring.

Reducing the risk of allergies in childhood

Plan breast-feeding carefully!  The best scenario is at least 4 months exclusive breast feeding with no top-up formula feeds in a mother who takes probiotic supplementation.  Maternal avoidance of allergenic foods during pregnancy and whilst breastfeeding does not seem to have any impact on the infant’s allergic status. Allergic sensitisation tends to occur very early in life through minor traces of allergens (inhalants and foods) being breathed in the air and contact with the skin when handling the infant after touching foods.  Although breast-feeding is the recommended form of infant feeding as it provides the best nutrients and immune protection, once sensitised, traces of food allergens can pass into breast milk.  Once the infant is sensitised to a particular food allergen, the breastfeeding mother needs to then strictly avoid that allergy provoking foodstuff in their own diet.  Traces of these allergy provoking foods can be found in the mother’s breast milk shortly after eating them and this could possibly lead to allergic symptoms in the baby [2].  Nursing mothers need to be careful not to use nipple creams that contain peanut (Arachis) or nut oil extracts, as these may also lead to nut sensitisation in the baby.

Paradoxically, a home environment that is meticulously sterile and contains no animals at all might actually promote allergy development in the newborn.  This is the basis of the “Hygiene Hypothesis”.  The “dirtier” the infants early life environment (first 6 months of life), the less likely that allergies will develop!  We find that babies born into large families and siblings, with early exposure to usual childhood viruses and those born on livestock farms and who drink unpasteurised milk are less likely to develop allergies.  Those born into families with only a few siblings and no exposure to dirt, animals or exposed to antibiotics early in life are more prone to develop allergies.  Early exposure to day care environments at a few weeks of age, may also reduce allergies.  There is no evidence that childhood immunisations are detrimental or promote allergy development; and the converse may be true with Tuberculosis (BCG) immunisation conferring some allergy protective effect.  Natural bowel organisms such as Lactobacilli GG and Bifidobacteria bifidum seem to have an allergy protective effect especially in eczema.   “Good” maternal bowel “germs” may enhance the establishment of similar organisms in the newborn’s bowel through vaginal delivery and first nursing and reduce the risk of allergy development.  Allergy-prone populations have a higher prevalence of bowel germ colonisation with clostridia, coliforms and staphylococcal bacteria versus non allergic populations with lacto-bacilli and bifidobacteria

Special attention should be given to protecting the newborn from allergens and improving the “barrier-effect” of the skin.  We recommend using liberal bland moisturisers or emollients on the skin, avoiding perfumed soaps, paraben preservatives, lanolin and all biological (enzyme-enriched) detergents.  Cotton clothing and mittens are preferable to synthetic and woollen clothes. Bath additives and bubble baths should be avoided only use products such as Oilatum in the bath.  Pregnant mothers can safely take chlorphenamine and loratadine in pregnancy and cetirizine and loratadine whilst breastfeeding.  Carefully read labels and avoid Vitamin and medications with colours added. Even herbal, organic or so-called “natural” medications should be viewed with suspicion, as these are possible sensitising agents.

Do’s and Don’ts of Pregnancy in Allergy-prone mothers

Pregnant mothers should:

  • Not smoke cigarettes and avoid passive smoking
  • Avoid alcohol intake
  • Consume modest amounts of allergy provoking foods such as peanuts, nuts, sesame, eggs and fish throughout pregnancy and don’t avoid them altogether.
  • Continue to take regular prescribed Preventer and Reliever asthma medication throughout pregnancy.  The Reliever beta agonists actually help to relax the uterine muscles.  Check that all prescription medication is safe to take in pregnancy. Ask your pharmacist.
  • Avoid all non-prescription drugs and vitamins that contain colourings or additives
  • We recommend avoiding any allergy provocative procedures in pregnancy such as Desensitisation Immunotherapy
  • Take probiotic (Lactobacillus GG) and prebiotic supplements during pregnancy
  • Pregnant women should continue to exercise, eat a balanced diet and get plenty of sleep
  • Supplement Vitamin D as lack of this vitamin may be implicated in subsequent asthma development in childhood.

Newborn babies should have:

  • Exclusive breast feeding for 4 to 6 months if possible
  • Only avoid exposure to cow’s milk and formula milk if there is a strong history suggestive of cows milk allergy.
  • Exposure to normal childhood germs and viruses
  • Avoid antibiotic treatment for viral illnesses unless absolutely essential
  • Avoid skin creams containing nut oils, perfume, lanolin and additives
  • Avoid all processed baby foods and rather eat freshly prepared foods from the age of 6 months.
  • Avoid all passive exposure to cigarette smoke
  • Immunisations should be given as usual


  • Intervention during pregnancy and allergic disease in the offspring Paediatr Allergy Immunol 2005: 16 ; 558-566
  • Chandra RK, Puri S, Hamad A. Influence of maternal diet during lactation and use of formula feeds on development of atopic eczema in high risk infants. BMJ 1989: 299; 228-30
  • Timing of Solid Food Introduction in Relation to Eczema, Asthma, Allergic Rhinitis, and Food and Inhalant Sensitization at the Age of 6 Years: Results From the Prospective Birth Cohort Study LISA. Anne Zutavern, Inken Brockow, et al, Pediatrics Vol 121, 1 January 2008, pages 183-191.
Written and researched by Dr Adrian Morris
First published May 2012 and last reviewed 0n 4th January 2019.