Breastfeeding and thrush: the difficulty getting a diagnosis

stack-of-petri-dishesAlthough many lactation specialists agree that breasts are susceptible to thrush (the candida fungus) when a woman is nursing, others feel that the yeast infection is ‘overdiagnosed and overtreated1.’ A quick perusal of the Mumsnet discussion forum shows that some health professionals are prepared to go a step further, and deny it is a problem at all (see breastfeeding and thrush: it’s complicated).

The scepticism that thrush can interfere with breastfeeding exists because at present there is no absolute proof that candida is the root cause of breastfeeding pain. A mother can become colonized with candida but remain infection-free, or can display many of the symptoms commonly associated with thrush (such as red, shiny, flaky or burning nipples) but test negative for it in the laboratory2.

This doesn’t mean that thrush isn’t a problem however: there are several controlled clinical studies that point to an association – not a perfect one, but a significant one nonetheless – between the presence of candida and certain symptoms suffered by breastfeeding mothers.

Evidence that thrush can affect breastfeeding mothers

Support for this relationship was provided by a study that assessed whether mothers who tested positive for candida shortly after they had given birth went on to develop the symptoms of thrush2,3. Nipple swabs and milk samples that were taken from 100 women at their two week post-birth check underwent microbiologic culturing to test for candida, and women completed two interviews to determine whether they had symptoms associated with thrush: one at the time the swabs were taken, and another 7 weeks later.

Although there was no association between colonization and symptoms initially, 20 of the 23 women colonized by candida went on to develop at least one of the symptoms of thrush (burning nipples, stabbing breast pain, shiny and/or red nipples). The percentage of cases (breasts rather than mothers, as it’s possible to be affected on only one side) with a positive or negative candida result that developed symptoms are listed below.

Nipple culture results (22 positive cases, 178 negative cases):

  • 95% of positive cases and 49% of negative cases reported sore nipples
  • 100% of positive cases and 33% of negative cases reported burning nipples
  • 82% of positive cases and 18% of negative cases reported non-stabbing breast pain
  • 91% of positive cases and 24% of negative cases reported stabbing breast pain
  • 45% of positive cases and 11% of negative cases reported shiny nipples
  • 36% of positive cases and 13% of negative cases reported flaky nipples

Milk culture results (32 positive cases, 168 negative cases):

  • 78% of positive cases and 50% of negative cases reported sore nipples
  • 81% of positive cases and 33% of negative cases reported burning nipples
  • 72% of positive cases and 16% of negative cases reported non-stabbing breast pain
  • 81% of positive cases and 21% of negative cases reported stabbing breast pain
  • 41% of positive cases and 10% of negative cases reported shiny nipples
  • 38% of positive cases and 11% of negative cases reported flaky nipples

Every symptom occurred at a significantly higher rate in the cases where candida had been detected. Each symptom was also reported in several negative cases, however, indicating either that the mothers had become colonized by candida after the initial test, or that the symptoms were caused by something else.

Another study investigating the link between the results of milk cultures and breastfeeding pain also reported that candida was found in a significantly greater proportion of women who were suffering from sharp, shooting breast pain: 6/20 (30%) of the women with pain tested positive for it, but only 6/78 (5%) of the no pain group4. This study also tested for levels of common bacteria, and found they did not differ significantly between the two groups.

Evidence that symptoms associated with thrush may be caused by something else

There are other experiments, however, which indicate that bacteria – rather than fungi – may be the culprit in some occurrences of breastfeeding pain. A study comparing culture results of 20 women with deep, stabbing pain, 20 with superficial nipple pain and 20 controls with no pain found an association between candida and superficial pain, and bacteria and deep pain: candida was found on the nipples of 1 of the control group, 12 of the superficial pain group and 10 of the deep pain group; and in the milk of 1 of the control group, 10 of the superficial pain group and 5 of the deep pain group5. By contrast, pathogenic bacteria were detected on the nipples of 4 of the control group, 11 of the superficial pain group and 19 of the deep pain group, and in the milk of 6 of the control group, 8 of the superficial pain group and 14 of the deep pain group.

Support for the idea that thrush does not underlie all breastfeeding pain is also provided by a recent study that compared levels of candida in the milk of 18 healthy breastfeeding mothers and 16 with thrush symptoms (sore, inflamed or traumatized nipples, intense stabbing or burning pain and painful breastfeeding that had not received any other diagnosis)6. The investigators were very careful to avoid contamination of the sample: nipples were thoroughly washed, and breasts were pumped for 12 minutes before any milk was collected. No evidence of candida was found in any of the samples, leading the authors to suggest that it does not infect milk ducts, and is unlikely to be the cause of the symptoms associated with thrush. They also go a step further, and suggest that positive nipple cultures cannot be trusted, as they may be contaminated by the baby’s saliva, which often contains candida. They conclude that, ‘candida infection on the mother’s skin remains a possibility, but it seems unlikely.’

This interpretation of the results seems fairly extreme. In previous studies, candida has been found to colonize milk (but not nipples)2 so the possibility that thrush may infect milk ducts cannot be ruled out. It is also not really appropriate to draw conclusions from the data about candida infection of the nipple, or the role of bacteria in breast pain, as neither of these things was actually examined. There is some evidence that bacteria may underlie certain instances of breast pain – it has been found at higher concentrations than candida in the milk of women suffering from deep pain5 – but this result conflicts with another reporting higher levels of candida in women suffering from a similar complaint4.

It is not only the role of bacteria that is hazy, however: despite the association between candida and symptoms reported in some studies, this link is far from concrete. Not every woman with the symptoms of thrush tests positive for candida, and some who are colonized by it never report symptoms. If you also consider that cultures themselves can be easily contaminated and may therefore be unreliable, the picture gets even more complicated.

Treating the symptoms of thrush

What does all this mean for breastfeeding women who appear to be suffering from thrush? Some researchers take the view that as the relationship isn’t sufficiently proven, women should not be treated with antifungal medication, or should receive it only as part of a controlled trial7. Others take a more pragmatic view, and suggest that such medication can actually have a useful diagnostic value: if the symptoms clear up after using an antifungal, then this ‘confirms’* that the symptoms were caused by candida8. This is far from an ideal solution (using such medications unnecessarily is expensive and increases the chances of fungi developing resistance to them), but it may be preferable to leaving women to suffer with very painful symptoms when there is chance they could be cured. Women who exhibit the symptoms of thrush when breastfeeding are at a very high risk of giving up3, so if there’s a medication that could stop this from happening, it may not be a bad idea to use it.

  1. Breastfeed Med. 2009 Jun;4(2):55.
  2. J Hum Lact. 2004 Aug;20(3):288-95.
  3. J Obstet Gynecol Neonatal Nurs. 2005 Jan-Feb;34(1):37-45.
  4. Am J Obstet Gynecol. 2007 Oct;197(4):424.e1-4.
  5. Gynecol Obstet Invest. 1998 Aug;46(2):73-4.
  6. Breastfeed Med. 2009 Jun;4(2):57-61
  7. Breast. 2002 Feb;11(1):88-90
  8. J Hum Lact. 1999 Dec;15(4):281-8.

*Of course, this doesn’t really confirm that a mother was suffering from thrush, as the alleviation of her symptoms may have been coincidental.

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Breastfeeding and thrush: it’s complicated

woman-doing-mathI sometimes feel as if I’ve experienced pretty much every breastfeeding problem going: sore/bleeding/fissured nipples; mastitis (although fortunately only the early stages); not enough milk; too much milk; and a very temperamental let-down reflex. One of the only things I haven’t suffered from is thrush – a fungal or yeast (candida) infection that allegedly causes excruciating nipple and breast pain. I use the word ‘allegedly’ simply because it is not always easy to determine whether the symptoms associated with thrush are definitely caused by a fungal infection, or whether they are in fact down to something else. I am not a thrush doubter – I think there is sufficient evidence to justify taking it very seriously, as does the NHS. Many health professionals who do not specialize in breastfeeding are yet to be convinced, however, as the Mumsnet discussions below testify:

(These are just a drop in the ocean – you will find all manner of breastfeeding ignorance from health professionals on these noticeboards. The GP who suggested a mother might pass mastitis on to her baby deserves a special mention.)

It isn’t just those outside the field who disagree about thrush: within the scientific literature there are conflicting results and opinions, as well as holes in clinical knowledge because the relevant research simply hasn’t been conducted. I’m currently wading through the published work in this area, and am finding it’s actually quite difficult to get to the bottom of the relationship between yeast infections and breastfeeding problems. As it’s important to try to make sense of it though, I’ll be writing several posts on it over the next few weeks, starting with one that attempts to address the controversy that still surrounds the diagnosis.

Hydrogel dressings for breastfeeding: ‘a clinical case study’

medicsIn the moist wound healing post, I discussed a number of peer-reviewed clinical studies that examine whether using dressings or creams to prevent nipples drying out helps them to heal more quickly (short answer: it doesn’t). While I was researching the post, I came across a ‘clinical case study’ on a hydrogel dressing manufacturer’s website, purporting to show the effectiveness of their product. As it is not really research, it wasn’t included in the moist wound healing post, but as it very much tries to appear as if it is, I thought it would useful to write about it anyway.

In the ‘study’, 10 women were supplied with hydrogel dressings within 24 hours of giving birth, and asked to wear them continually on both breasts when they weren’t feeding. Their effectiveness was measured, on the third and seventh days of wearing them, by asking the women to rate the levels of pain they experienced whilst they were breastfeeding, and in the time in between feeds. The scores, displayed in a rather unorthodox graph (where the between and during feed measures are inexplicably joined together with a line), appear to show that the dressings caused pain levels to gradually decline.

Of course, the fact that pain scores are lower on day 7 than day 3 does not necessarily mean the dressings are effective – the chances are, this would happen anyway. To demonstrate that the dressings cause the ratings to go down more quickly than usual, the paper Ziemer et al, 1990, is cited as evidence that without treatment it can take up to 12 days for nipple pain to improve. I have read this paper, and am a little surprised at the way the results have been interpreted: it actually reports that for the majority of women, nipple pain peaks on day 3, and declines thereafter1. If we assume that the ‘1990’ in the main body of text was in fact an error (there is no Ziemer et al, 1990, in the references at the end) and they actually meant to say Ziemer et al, 1995 (which is listed) the citation becomes even less appropriate. I have read this paper as well, and can tell you that the study that it reports ended at 7 days, and is therefore unable to say anything about nipple pain at 12 days2. There are numerous other studies not mentioned in the article that show that mean pain scores start to decline significantly within – who’d have thought? – 7 days of giving birth3.

The article concludes by saying:

The dressings’ moist wound healing properties were an aid in reducing pain and promoting nipple healing, without an increased risk of infection.

The observant among you will have spotted that neither wounds nor infections were monitored, so this claim is, of course, completely unfounded. It may also be wrong: research that has examined using hydrogel in a controlled setting reports that it may in fact delay wound healing and make mothers more vulnerable to infection4. Unsubstantiated or inaccurate statements about the effectiveness of a product are perhaps to be expected from a company trying to sell it. What is truly frustrating about this item of pseudo-science, however, is that it is endorsed by a midwife, lending it legitimacy. When women start breastfeeding they are often feeling stressed and vulnerable. If they can’t rely on health professionals to give them accurate, unbiased advice at this time, then it’s a pretty depressing state of affairs.

  1. West J Nurs Res. 1990 Dec;12(6):732-43; discussion 743-4.
  2. Nurs Res. 1995 Nov-Dec;44(6):347-51
  3. J Obstet Gynecol Neonatal Nurs. 2005 Jul-Aug;34(4):428-37.
  4. Arch Pediatr Adolesc Med. 1998 Nov;152(11):1077-82.

Should ‘moist wound healing’ principles be applied to cracked nipples?

pot-of-vaselineMaintaining a slightly damp, rather than dry, environment under a dressing has been shown in many studies to help wounds heal faster. Moisture prevents a scab from forming, which allows new epithelium cells to move across the surface of the wound more quickly, and reduces the time it takes it to close1.

As the technique appears to improve the healing rates of a range of skin lesions2, it has been suggested that its benefits may extend to cracked nipples3, and there are now several off-the-shelf creams and dressings that claim to maintain a moist environment, and thus help the healing process. The inference is not, at first glance, unreasonable – if moisture helps skin to regenerate more quickly, then it may well help injured nipples to recover too. It is important to remember, however, that nipples are subject to a unique set of circumstances when a mother is breastfeeding, so it is also quite possible that the application of the technique might not be appropriate. Is there any scientific evidence that applying moist wound healing principles can aid the recovery of cracked or injured nipples?

In a study comparing dressings made from hydrogel with lanolin (both classified by the Breastfeeding Network as having ‘moist wound healing’ properties)4, 106 mothers were allocated at random to one of two groups: the first was given hydrogel dressings to use between feeds; the second was given lanolin cream. Mothers started using the treatments within 24 hours of giving birth, and their effectiveness was assessed via telephone interviews 3, 4 or 5, 7, 10 and 12 days later. The researchers found mothers reported significantly lower pain scores (a difference of just under 1 point, on a scale of 1-5) in the hydrogel group on days 10 and 12.

There were a couple of problems with this study (actually, there were several, but I’ll limit it to the major ones). Firstly, there was no baseline group of mothers not applying anything to their nipples, so it is not possible to say whether either treatment was better than simply leaving nipples alone. A second issue is that the people conducting the interview were aware, when they spoke to the participants, which treatment they were receiving. The researchers claim that to have conducted the study blind would have been ‘impossible’, an unsubstantiated and somewhat odd statement, as it would appear to be completely possible to interview a mother over the phone without knowing what she had on her nipples. Knowledge of the treatment group in this type of study is a problem if there is any chance that the researcher may have a bias towards a particular treatment, as they may subconsciously influence the patients’ responses. It may be worth mentioning at this point that the research was funded by Tyco, the manufacturers of the dressings.

These criticisms are, however, a digression. The main thing to note about this research is that it did not test whether the dressings actually helped wounds to heal. Although moist wound healing is touted in the introduction as the ‘science bit’ justifying the use of the dressings, it is not mentioned anywhere in the procedure or the results.

A hospital-funded study comparing hydrogel and lanolin – this time documenting the impact that the treatments had on bleeding and cracked nipples – did not find the dressings to be quite so effective5. Researchers who were blind to the treatment group rated nipples as healing significantly better when women used lanolin with breast shells, rather than hydrogel dressings. Self-reported measures of pain were also significantly lower in the lanolin group. A final point worth mentioning is that the study was halted early, due to a third of the 21 women in the hydrogel dressing group developing an infection.

Although this study compared two treatments, it is again compromised by the lack of a proper control group. We can see that lanolin appears to result in improved healing and lower pain scores when it is compared with hydrogel, but we still do not have any evidence that moist wound healing techniques are useful for treating injured nipples when breastfeeding – to ascertain this requires a control group where mothers keep their nipples dry.

So far, there appear to be only two studies that have looked at this issue. An experiment published in 1995 examined whether using a polyethylene adhesive dressing had any effect on the development of nipple redness, fissures and pain6. 50 mothers took part in the study, using a dressing on one nipple, and leaving the other untreated. Although the mothers reported less pain when feeding with the treated nipples, the researchers caution that this may simply have been because of the ‘Hawthorne Effect’ (the mere fact there is an intervention is enough to cause an improvement.) The dressings made no difference to the development or healing of fissures or redness, as reported by observers blind to the treatment group. 16% of the participants dropped out due to finding the dressings uncomfortable, and 66% said they found it uncomfortable to remove them – something they had to do before every feed.

A more recent study looked specifically at the effect of lanolin on the healing of nipple fissures7. 225 women, all with fissures, were randomly allocated to one of three groups: in the first group mothers applied lanolin 3 times a day; in the second they applied breast milk after each feed; in the third they applied nothing. The appearance of their nipples was assessed 3, 5, 7 and 10 days after starting the treatment by researchers who did not know which group the mothers were assigned to. There was no significant difference in healing time between the breast milk and no-treatment groups. The nipples of the women using lanolin, however, took significantly longer to heal (45% of this group took longer than 7 days, as opposed to 32% of the milk group, and 25% of the no-treatment group).

There is another area of research, which does not examine the use of moist wound healing directly, but is still relevant to the debate. Broken skin makes nipples vulnerable to infection8, which may mean there is an additional problem with keeping nipples damp, rather than dry: organisms like thrush are known to thrive in warm, moist environments9.

Given the possible risk of infection, and the evidence that maintaining a moist environment around cracked nipples may potentially delay the healing process, it seems to unwise to recommend the application of the products described above to mothers with cracked or fissured nipples. In spite of this, they continue to be promoted by both commercial companies and health professionals on scientific grounds. Until evidence that genuinely supports its use is found, presenting moist wound healing to mothers as a clinically tested treatment is at best misguided, and at worst dishonest.

  1. Nature. 1962 Jan 20;193:293-4.
  2. Br J Nurs. 2008 Aug 14-Sep 10;17(15):S4, S6, S8 passim.
  3. J Hum Lact. 1997 Dec;13(4):313-8.
  4. J Obstet Gynecol Neonatal Nurs. 2003 Jul-Aug;32(4):486-94.
  5. Arch Pediatr Adolesc Med. 1998 Nov;152(11):1077-82.
  6. Nurs Res. 1995 Nov-Dec;44(6):347-51
  7. Saudi Med J. 2005 Aug;26(8):1231-4
  8. J Hum Lact. 1991 Dec;7(4):177-81.
  9. Hum Lact. 1999 Dec;15(4):281-8.

Can breastfeeding affect your sex life?

unmade-bedIn the initial period after giving birth, sex tends not to be a top priority. Slowly, as you start to feel less ‘delicate’, and days become distinguishable from nights again, it creeps back up the agenda, and by 6-12 weeks, most women have recommenced intimate relations. The speed with which you get back to sex may be influenced by the way in which you feed your baby, however: there is evidence that if women formula feed, they may be up for it significantly sooner than if they breastfeed1.

Determining how exactly breastfeeding affects a mother’s sex life is a complicated business. The body of scientific literature looking at this issue spans several decades, and whilst it contains some interesting observations, it is also littered with apparently contradictory results. In their 1966 work, ‘Human Sexual Response,’ William Masters and Virginia Johnson reported that all 24 of the breastfeeding women they studied experienced ‘enhanced sexuality’ compared to non-nursing mothers. This result does appear to be something of an anomaly, however; whilst it is certainly not the case that all breastfeeding women experience a pronounced drop in libido, there is a tendency for them to be less interested in sex, and less likely to engage in it than formula feeders.

Of five studies comparing the sexual experiences of breast feeding and formula feeding women, one reported that feeding method did not appear to make any difference2. The remaining four found that breastfeeding mothers were less interested in having sex3,4, less likely to be having it1,3, and more likely to find it painful when they did5.

A study that monitored women during the weaning process also suggests nursing may suppress sexual activity6. Mothers who had been breastfeeding for at least 6 months completed a daily questionnaire about their health and how they were feeling until a month after they had weaned their babies. The responses they gave in the 4 weeks before weaning were then compared with their responses in the 4 weeks after.

Within 3-4 weeks of stopping breastfeeding, the mothers in the study reported a significant increase in sexual activity. They also reported an improvement in mood and a decline in fatigue, and the authors suggest that this may in part explain the women’s increased appetite for sex. Other research has reported that the lower sex drive of breastfeeding women exists irrespective of tiredness or depression, however, so it is likely that there are other factors underlying the issue4.

One potential culprit is the differing hormone levels that occur in women who are nursing. High prolactin and low oestrogen levels are thought to reduce vaginal lubrication, and as these hormone levels are frequently found in breastfeeding mothers, the theory goes that this may in turn reduce their sexual activity1. Although this is a reasonable hypothesis, a direct link between prolactin/oestrogen levels and lower sexual desire in breastfeeding women has yet to be demonstrated: in a study monitoring levels of these hormones directly, no correlation was found between the two7. The study did find a relationship between very low levels of the sex hormones testosterone and androstenedione and ‘a severe reduction in sexual interest’, which affected five women in the breastfeeding group in the study, and none in the formula feeding group. It is important to point out, however, that the formula group was much smaller (14 breastfeeders were compared with only 6 formula feeders), so while the results indicate that breastfeeding may result in lower levels of these hormones, they don’t provide conclusive proof.

An alternative explanation is that breastfeeding women may be less interested in sex as they have an ‘intimate touching need’ satisfied by nursing, and are therefore less likely to seek its fulfilment through sex1. Again, however, this is speculation: it’s possible it may have an impact in some relationships, but it has not been evaluated scientifically.

So far, the research looking at the relationship between breastfeeding and sex hasn’t provided any clear answers. There is evidence that breastfeeding women are more likely to report a lack of interest in sex, or find it less comfortable, but this is not something that affects nursing mothers across the board – many report enjoying sex, and some have even said that their sexual relationship during this period is better than before they gave birth8! Whether this because of, or in spite of breastfeeding is impossible to know, but it indicates that nursing your baby will not necessarily condemn you to a poor sex life. Having said that, the libido of some mothers does appear to be seriously diminished during breastfeeding. The reason for this isn’t clear, but it could be because these women are experiencing particularly low levels of certain sex hormones.

If you do find sex particularly unappealing while you’re breastfeeding, the good news is that it doesn’t appear to last forever. A large study found that although breastfeeding women reported less interest in sex than formula feeders to start with, this difference had disappeared by 12 months4, so however long you intend to breastfeed, it seems your shouldn’t have to wait more than a year for your libido to get back to normal.

  1. J Fam Pract. 1998 Oct;47(4):305-8.
  2. Br J Obstet Gynaecol. 1981 Sep;88(9):882-9.
  3. J Sex Res. 2002 May;39(2):94-103.
  4. Br J Obstet Gynaecol. 1997 Mar;104(3):330-5.
  5. BJOG. 2000 Feb;107(2):186-95
  6. Obstet Gynecol. 1994 Nov;84(5):872-6.
  7. Br J Psychiatry. 1986 Jan;148:74-9.
  8. J Midwifery Womens Health. 2000 May-Jun;45(3):227-37.

Can ‘full term’ babies born before 40 weeks find it harder to breastfeed?

stork-carrying-babyThe fact that premature, or preterm, babies can experience difficulties breastfeeding is well documented. Neurological immaturity, poor muscle tone and underdeveloped reflexes can all affect the ability to perform suckling movements, so babies born early generally don’t find it as easy to feed directly from the breast as babies born at full term1. The length of time that constitutes ‘full term’ is slightly hazy, however. Although the average pregnancy lasts 40 weeks, it is usually from 37 weeks gestation that babies are regarded as being sufficiently mature to qualify as term. There is some evidence, however, that babies born after 37 weeks, but before 40, may not always be as well developed as those born later, and a large study in Australia suggests that this could potentially make it more difficult for them to breastfeed2.

The study looked at the impact that length of gestation had on breastfeeding rates in a sample of 3600 children born over the period of a year. Babies were divided into three groups: those born before 37 weeks (preterm); those born at 37-39 weeks (early full term); and those born at 40 weeks and over (late full term). Preterm babies were the least likely to be breastfed – only 88% of mothers in this group initiated breastfeeding (compared to 92% in the early full term group and 94% in the late full term group), but this could have been due to social factors such as the age and level of education. Although there appeared to be a small difference in the initial breastfeeding rates of the early and late full term babies, it was not statistically significant. 6 months later, however, when breastfeeding status was next documented, the gap had widened to a significant level.

Pre-term babies were still the least likely to be breastfed – only 41% were still being nursed at this point, compared to 61% of the late full term babies. 55% of the early full term babies were still breastfed at 6 months – more than in the preterm group, but significantly fewer than in the older full term group. The fact that there was a difference between the full term groups at 6 months, but not initially, is important as it indicates that early full term babies may be at greater risk of breastfeeding failure: mothers of the younger babies were as likely to start breastfeeding, but they were more likely to stop before their babies reached 6 months. This difference can’t be explained by the other factors recorded in the study, and the underlying reasons for it aren’t clear, but the authors suggest that it may have arisen due to subtle immaturity, such as underdeveloped mouth muscles, that can affect babies born before 40 weeks, even when they have passed the 37 week milestone.

If your baby is born slightly early, the chances are, of course, that she won’t have any major problems breastfeeding. In the study reported above, the majority of babies born after 36 weeks were still breastfeeding 6 months later, so the prognosis is good. It’s still worth noting that a gestation period under 40 weeks might decrease the chance of a mother continuing to breastfeed, however, so any difficulties that do arise can be picked up and addressed before it’s too late. With a little patience and practice even very preterm babies can adjust to breastfeeding as they get older1, so dealing with problems caused by mild immaturity is comparatively straightforward. The key is being aware they may occur: recognizing that for some babies born between 37 and 39 weeks breastfeeding may be difficult for a short time – and providing the right support to mothers through this period – would help ensure that many more babies born slightly early are able to successfully achieve exclusive breastfeeding.

  1. Infant, 2005 July; 1(4):111-115.
  2. Arch Dis Child Fetal Neonatal Ed. 2008 Nov;93(6):F448-50.

The antibacterial properties of breast milk

lab_technicianMany years ago, breast milk was thought to be sterile. While this is far from being the case (it actually contains all manner of germs1), the role it plays in helping keep babies free from harmful disease means it does display some pretty impressive bug-busting capacities.

The immunological components of breast milk help to protect both a mother’s breast and her baby from infection during feeding, as well as aiding the development of the baby’s immune system2. They also have another useful consequence, however: protecting breast milk from disease for some time after it has been expressed, enabling it to be stored. Several studies have examined whether it is safe to keep expressed milk for short periods, and there is general agreement that it can be stored for 8 hours at room temperature (25 degrees C), for three days in the fridge (4 degrees C) and for up to a year in the freezer (-20 degrees C) without any increase in the levels of pathogens (harmful bacteria) it contains3.

Not only does breast milk inhibit the growth of pathogens, however – it actively reduces them. This was convincingly demonstrated in a piece of research examining what happened to milk during short term storage4. Milk was collected from 9 mothers and divided into three samples: the first was analyzed the same day; the second was refrigerated (at 4 to 6 degrees C) for 48 hours; and the third was refrigerated for 72 hours. Each sample was then contaminated with an E.coli solution (the kind of nasty bacteria that dwells in toilets) and left for two hours. When the samples were tested, levels of E.coli had reduced by 80% in both the milk that was fresh and the milk that was 48 hours old. Levels had also diminished in the 3 day-old milk, but only by around 10%, indicating that the antibacterial properties, whilst still present, had started to degrade by this point.

If your baby needs to feed from a bottle or cup, a considerable body of research indicates that it’s safe to give him breast milk that has been stored in the fridge for up to three days, or in the freezer for several months. There is also evidence that if the milk you express does come into contact with germs (keeping pumping equipment sterile in your bag at work isn’t always easy), then the bactericidal components of breast milk should be able to take care of them, providing the milk is under two days old. There may still be potential issues associated with feeding stored, rather than fresh breast milk to your baby: various chemical changes occur in milk once it has left the body, and it’s possible some of these may affect its nutritional value3,5,6. Nevertheless, expressed breast milk remains a healthy alternative to formula, and as a result of its antibacterial qualities, you can rest assured that if your baby can’t feed from you directly, he still has a safe source of food and drink.

  1. Mastitis: causes and management. World Health Organization; 2000.
  2. Adv Food Nutr Res. 2008;54:45-80.
  3. Acta Paediatr Suppl. 1999 Aug;88(430):14-8.
  4. J Pediatr Gastroenterol Nutr. 2007 Aug;45(2):275-7.
  5. Acta Paediatr. 2001 Jul;90(7):813-5.
  6. Biofactors. 2004;20(3):129-37.