There are many reasons why infants suddenly, and infuriatingly, go off their feeds - but if your baby has strange white patches inside their mouth, it's likely they are suffering from thrush.
What is it?
Thrush is a yeast infection caused by a fungus called candida albicans. It occurs naturally within the mouth, but occasionally levels of the fungus can increase and an infection will occur.
Most common in babies aged between one and two months old (it does occur in older babies and even toddlers too, but more rarely) the obvious symptoms of thrush are white patches in the mouth - look for them on the tongue, gums, roof of the mouth and the insides of the cheeks. The patches look a bit like little specks of cottage cheese or milk curds: if you rub them, they will come away, but the area underneath might look red and rather sore.
There are various reason why babies get thrush. If mum had a bout of it and gave birth vaginally, it could have been passed on that way. Antibiotics (either baby taking them, or mum taking them and passing them on through her breast milk) can cause it too - because while the medicine is busy getting rid of the nasties that are causing illness, it is also, unfortunately, reducing levels of 'good bacteria', and this can, in turn, lead to higher amounts of candida.
Young babies are prone to to thrush because their immune systems are still developing, meaning they find it harder to resist infection. For that reason, premature babies in particular, are at risk of developing it. Although thrush is not very pleasant, it is not a serious condition. The soreness in your baby's mouth, however, might well prevent them from feeding properly, so it can lead to dehydration.
What can I do?
In many cases, thrush is mild and will go of its own accord. However, if you think your baby has thrush, you should take them to your GP who will be able diagnose it just by looking in their mouth. If necessary, your doctor will prescribe some anti-fungal medicine - either a gel called miconazole (which should be applied to the infected areas with a clean finger after feeds), or a liquid called nystatin. It could take a week or so for the thrush to clear up, but if it hasn't gone after seven days, go back to your doctor. Also, if your baby develops a fever, go back to the surgery, because it could be indicative of a different infection.
Babies over three months old can be given the correct dosage of liquid paracetamol or ibuprofen, which will help relieve any soreness in their mouth and hopefully encourage them to take their feeds properly (a hungry baby is never a happy baby!).
To prevent the thrush infection being passed back and forth, you should sterilise bottles and teats regularly. If you are breastfeeding, wash your nipples with water and dry them before and after feeds, as this will help to prevent the infection being transmitted to you (it can occasionally occur on the nipples, ouch).
Any toys or teething rings your baby likes to put in their mouth should be sterilised too, and running your baby's clothes through a hot wash will get rid of any fungus attached to them. Some doctors may suggest giving your baby's mouth a quick rinse with some sterilised water after their feed, to wash away the milk.
What else could it be?
Thrush is fairly easy to diagnose by the white patches in the mouth - however, sometimes milk residue on the tongue can look similar. Brush the white area with your finger - if it comes away but there is no redness or soreness underneath, it is probably just milk residue. If your baby continues to fuss during feeds, they might be teething. Other illnesses that can cause soreness in the mouth, such as hand, foot and mouth disease, will be accompanied by a fever.