Prior to my brush with it, I thought that mastitis was caused by a bacterial infection. This is not completely unreasonable, given that this is precisely how numerous ‘health’ websites define it (FreeMD, eMedicineHealth, HealthSquare to name just a few). When you consider that the symptoms of mastitis can include a fever as well as redness, lumps and pain in the breasts, and treatment can involve antibiotics, the definition seems to make sense.
Unfortunately, it turns out to be somewhat misleading. Whilst bacterial infection may play a part in mastitis, it is in fact inflammation of the breast tissue that is at the root of the condition, and causes the majority of the symptoms. The World Health Organization describes mastitis as ‘an inflammatory condition of the breast, which may or may not be associated with infection’1. They summarize the uncertain relationship between bacterial infection and mastitis as follows:
Many lactating women who have potentially pathogenic bacteria on their skin or in their milk do not develop mastitis.
Many women who do develop mastitis do not have pathogenic organisms in their milk.
This basically means that you can be carrying the bacteria associated with mastitis – and even have it in your milk – without developing the condition, and conversely, you can succumb to mastitis when there is no evidence you’re carrying the bacteria.
So, if mastitis isn’t due to an infection, what does cause it? It appears that the inflammation that characterizes mastitis is a consequence of ‘milk stasis’: milk is produced, but then remains in the breast, rather than coming out during feeding. Milk stasis can occur for many reasons, including blockages in the ducts, a decrease in feeding frequency and poor attachment1,4. It’s also possible that stress might play a role, by both increasing milk production and delaying the letdown reflex2. Why milk stasis goes on to cause inflammation isn’t so clear, though it could result from inflammatory substances found in milk irritating the breast tissue, or an immune reaction to certain milk proteins3.
Although bacterial infection is not often the primary cause of mastitis, it is sometimes thought to exacerbate the symptoms3. Determining the precise role it plays, however, is a tricky business. Firstly, it is very hard to ensure that milk cultures are sterile, so it isn’t always possible to know that the bacteria found in a woman’s milk haven’t in fact come from her skin when the sample was taken1. Secondly, as stated above, harmful bacteria can be found in the milk of women who don’t have mastitis, indicating that there is not a simple cause and effect relationship between the two. One possibility is that mild changes initiated by milk stasis may be exacerbated by bacterial activity: symptoms could be considered to be on a scale, from a reduction in milk output but no pain (known as subclinical mastitis), to breast abscess and severe pain, with increasing amounts of bacterial involvement as you move from one end to the other3.
What does all this mean if you find yourself suffering from mastitis? Perhaps the most important thing to remember is that the symptoms are probably due to a milk flow problem, so your top priority should be to address any causes of this. This might include making sure your baby is properly latched on, feeding more frequently and emptying the breast properly at each feed. Many doctors also choose to treat mastitis with antibiotics, although there is a lack of consensus as to which ones to use, and even whether it’s appropriate to use them at all (see when should mastitis be treated with antibiotics?). Whether or not you take medication, the most important thing is to keep the milk moving. Whilst feeding with mastitis doesn’t appear to pose a risk to you or your baby, stopping could well do: not only will it make the symptoms worse, but it will almost certainly jeopardize your milk supply5. Mastitis is a common reason for giving up breastfeeding, but it needn’t be – focus on sorting out your feeding technique and you should hopefully make a rapid recovery.