Digestive symptoms of CMA in infants: Blood in stool, diarrhoea, constipation and more

Your baby may show signs of reflux, such as excessive crying, back arching or irritability, with or without regurgitation (spitting up) or vomiting. Symptoms often begin before 8 weeks old and are very common, affecting up to 40% of babies.²  Your baby’s stomach is small, and fluids can easily flow upwards. Mild reflux usually improves by age one without treatment.³  Seek medical support if your baby has excessive vomiting, not gaining weight as expected and becoming very distressed. CMA may be considered.^1,4

Changes in your baby’s stools are common. Breastfed/chestfed babies often have soft, loose, or seedy stools several times a day or every few days, while formula‑fed babies tend to have a more regular pattern.  Diarrhoea may appear as very watery stools that soak into the nappy, usually three or more times a day. The colour of the stools can sometimes be green (some specialist formulas also cause this), mucus or foul smelling. If stools are frequent watery stools or occur with other symptoms, seek assessment to rule out infection or CMA.

Constipation is when your baby passes stools less often, pellet‑like, and are difficult to pass. It is a common concern in infants.  If constipation is the only symptom, it is less likely to be CMA.⁵ Young infants often strain when passing stools because their tummy muscles are still developing, this can be normal. For infants not responding to usual treatments for constipation, CMA may be considered.

Mucus in stools often appear as a slimy or stringy, jelly‑like substance in your baby’s nappy. This can occur normally, for example if your baby is unwell, teething, or after immunisations. Blood in the stool may look like black/red specks or red streaks, which can understandably be alarming. A medical professional will help identify the cause. If there is very minimal blood in an exclusively breastfed/chestfed baby, your healthcare professional may monitor.⁶ In other cases, CMA may be suspected and a trial of removing cow’s milk protein may be advised, it is important to have a medical assessment for the correct guidance for your baby.

Colic is common in babies up to around 5 months of age⁷ and affects 1 in 5 babies.⁸ Colic is your baby being very fussy, unexplained crying, drawing legs up to the tummy and clenched fists with no obvious cause in a healthy baby with good growth. Symptoms are often worse later in the day. There is limited evidence to support making dietary changes for colic alone.⁹ If CMA is being considered, your baby is likely to have other symptoms alongside colic and irritability.

Newborn babies have naturally underdeveloped digestive systems, making it harder for them to process milk, this can lead to gas and sometimes bloating. They may also swallow air while feeding or crying.  Burping or winding your baby during or after feeds can help ease these symptoms, and most babies improve over time without needing any major changes.  If very persistent symptoms alongside uncontrolled crying, consider seeking medical support. CMA is more likely if there are other symptoms alongside this for example many watery stools, blood in the stools or poor weight gain.

Some babies with digestive symptoms may struggle to gain weight, as inflammation in the gut can temporarily affect how well nutrients are absorbed.⁶ Feeding difficulties such as refusing feeds, poor sleep, or frequent vomiting can also impact weight gain. CMA can be considered if there is poor weight gain alongside other digestive symptoms. Always seek support if your baby is struggling to gain weight.

If CMA is suspected your healthcare professional may advise that milk protein is removed from the diet. It may take 2-4 weeks for symptoms to settle.  Whether your baby is breastfeeding/chestfeeding, on a milk-free diet or on a hypoallergenic formula, it is important to be consistent with the plan for your baby to remain well. Monitor the symptoms and escalate any concerns.  After 2-4 weeks a re-challenge of milk back into mum’s/feeding parent’s diet or via formula may be advised to confirm the diagnosis.

Nutricia offers a range of additional resources that you may find helpful. These can be accessed via the Nutricia website, where you'll find dedicated sections providing further practical information and support. If you'd like any additional guidance, the Nutricia Resource Centre team is always happy to help on 03457 623653.

Written by Laura Phillips. Paediatric Allergy Dietitian

Laura qualified as a Dietitian from the University of Surrey in 2003.  She found a passion for working in paediatric allergy when working in an MDT clinic at a tertiary London Hospital. For the last 13 years, Laura has worked in secondary care NHS based allergy and dietetic clinics.  Laura is currently the co-chair of the BDA Food Allergy Specialist group and provides advisory work to Allergy UK.