Your baby suddenly starting to throw up whatever he ate can be pretty scary, both for you and your baby. It is normal for him to cry as it is a new and rather unpleasant experience, but your baby vomiting does not necessarily mean that you need to run and call your pediatrician.
Baby Vomiting – Causes and Associated Symptoms
One of the principle reasons for babies vomiting so frequently is the small size of their stomach after birth. Being no larger than a golf ball, with the valves and muscles around it still immature, it is easy for the stomach to become too full with its contents sent back up again at simple stimulations such as burping and hiccups . Even a harmless bout of coughing may trigger the gag reflex, making your baby throw up his dinner.
Parents often get worried when their little ones vomit up small amounts of partially digested, cottage-cheese like milk a few hours after a feeding. But in most cases, there is nothing to worry about if your baby continues to feed normally. Since the vomiting is coming a few hours after a feed, the milk is already mixed with the stomach acids in your baby’s digestive tract, which gives it a curdled appearance.
You can look out for other warning signs as vomiting is often not a cause for concern if there are no other symptoms or if your baby is otherwise fine and happy [2, 3].
Baby vomiting clear/whitish fluid but no fever
Vomiting in newborn infants – clearing up the system after birth
It is common for babies to vomit for a few weeks after birth as their body is still working to eliminate any residual amniotic fluid in the stomach from their days in the womb. So, there is usually nothing to worry about when your infant vomits up clear or whitish mucus as it is just the amniotic fluid, mixed with the milk he has been drinking and the mucus produced by his stomach lining. Sometimes, the mucus may be quite thick, making the baby look like he is choking, even going blue or red in the face while throwing up [4, 5].
It is also normal for your baby to vomit clear fluid during the teething period as he swallows all the excess saliva produced during this time.
Tips to help your baby: In most cases, there is nothing to worry about as he will be able to handle it himself. You can sit him upright or gently pick him up and place him over your shoulder so he may spit the mucus out or swallow it more easily .
Baby vomiting and diarrhea with/without fever
Gastroenteritis or stomach flu
A viral infection of the stomach, it is more common in babies and toddlers below two years of age, but may affect kids of all ages. Younger children are more susceptible to the condition as they may easily catch the virus from other children or even adults . It is often caused by rotavirus, with other viral causes present as well . The vomiting may stop after a couple of days, but diarrhea may last for up to a week .
Symptoms: Diarrhea, stomach pain, unwillingness to eat or drink, along with low or no fever 
Prevention: Rotavirus Vaccine 
Treatment: Fluids to prevent dehydration, consult doctor for medications 
A common cold may also cause your baby to throw up while having a fever, stuffy nose, diarrhea and loss of appetite .
Baby vomiting and high fever with skin rashes
An inflammatory condition of the brain and spinal cord membranes (meanings), it can be bacterial or viral, with the former being much more serious (possibly life-threatening) than the latter . May go unnoticed at first as the symptoms are similar to those caused by common flu. Newborn babies are at a higher risk as their immune systems are not yet fully developed .
Symptoms: High fever/lower than normal body temperature, shrieking or loud crying, sensitivity to light, feeding difficulty, bulging fontanels and skin rashes [13, 14]
Prevention: Bacterial meningitis – Haemophilus influenzae type b (Hib) vaccine ; viral meningitis – Avoiding contact with contaminated objects
Treatment: Medical intervention required
Frequent vomiting with feeding difficulty and persistent coughing but no fever
Gastroesophageal Reflux Disease (GERD)
Acid reflux in babies is quite common and usually harmless; but in some cases, a severe GERD may even affect the nerves, muscles, and brain. The developing digestive system is yet again the commonly responsible factor for an acid reflux in newborns .
Symptoms: Colic, wheezing and breathing problems, poor growth, pneumonia 
Treatment: For mild acid reflux – Keep the baby’s head elevated for some time after each feeding, Try feeding in small amounts more frequently, Give soft, solid foods (for older babies); For GERD – Call your pediatrician 
Projectile vomiting after feeding in infants
Occasional projectile vomiting or throwing up forcefully may be normal in newborns with their immature system. However, forceful vomiting occurring frequently or after every feeding is a characteristic symptom of pyloric stenosis – a serious condition where the muscles in the opening between the stomach and duodenum (pylorus) become enlarged, preventing smooth passage of the food from the stomach [2, 18].
Symptoms: Small visible waves on his abdomen after feeding, moving from left to right as the stomach tries empty its contents, your baby wanting to feed soon after throwing up, abnormal weight loss and signs of dehydration (e.g. dry mouth, no wet diapers in 5-6 hours at a stretch) [19, 20]
Treatment: Surgery to open up the pylorus
Vomiting frequently after eating, along with rashes
If your baby throws up almost always after a feed, and has red bumps or rashes around his mouth, behind the knees, on the neck or arms, especially the crooks of the elbows, he may be allergic to the milk or formula he is drinking . In case he already eats solid foods then he may be allergic to a certain fruit or vegetable. Without early detection and care, an allergy may lead to serious symptoms like swollen mouth and tongue or even shortness of breath .
Treatment: Immediate medical care
Bright greenish/yellow vomit (vomiting bile)
This unusual color generally indicates the presence of bile in vomit, which may be resulting from a meconium blockage , birth defects like gastrointestinal obstruction  or a volvulus (twisted bowel) . The first two conditions are usually detected in newborns within the first few weeks of their life while the last one may develop in older children .
Treatment: All the possible underlying conditions call for immediate medical intervention
Baby vomiting blood
Blood in vomit is not always a cause of worry unless your baby has frequent blood vomit for hours or days. It is normal for newborns to have a little blood in their vomit as babies often swallow some blood during delivery, which is then eliminated from their system over the hours after birth . Having a nosebleed or a small cut in the mouth can also make your baby throw up blood within the next 6 hours . In some cases, forceful vomiting may also cause tiny cuts in the esophageal lining, causing some blood to be present in the vomit .
Treatment: Not necessary unless there is a serious underlying condition that may need medical care
Vomiting at night
It is normal for you to become concerned if your baby is vomiting every night after you feed him. There is a condition named cyclic vomiting syndrome (CVS) that causes an episode of vomiting around the same time every day, being more common at night or early in the morning . However, in most cases it is nothing as serious, with the vomiting occurring due to a higher amount of feeding to make the baby sleep through the night.
Treatment: Smaller, more frequent feedings at night; CVS usually goes away as your child grows, but may need medical treatment in some cases
When to call the doctor for Baby Vomiting
- Baby running a high temperature and/or is severely constipated
- Vomit contains blood that looks like small coffee granules .
- Baby’s belly feeling bloated, hard and/or painful before and after vomiting
- Baby start vomiting after a fall or a head injury 
- Constant vomiting for days, making baby unable to keep anything down
- Baby unwilling to feed, having difficulty hearing on one side, not sleeping well, and looking fussy or uncomfortable when lying down (might be an ear infection)
- References +
- http://www.webmd.com/parenting/baby/spitting-up, http://similac.com/feeding-nutrition/spit-up-and-vomit