When should vomiting make me worry?

What the evidence says

Most vomiting in kids is from a stomach bug and settles on its own within a day. The main danger is dehydration, so watch for fewer wet diapers or trips to the bathroom, no tears when crying, a dry mouth, unusual sleepiness, or a baby who cannot keep any fluid down at all. Some signs mean you should call your doctor or go to the emergency department right away: vomit that is green or bile-coloured, vomit with blood or a coffee-ground appearance, a young infant with forceful projectile vomiting (which can signal pyloric stenosis, usually appearing between 2-8 weeks of age), or vomiting lasting more than about 4-6 hours in a young infant or 24 hours in an older child.

If vomiting follows a bump to the head, it is one of the warning signs doctors use to decide whether a brain scan is needed, especially with repeated vomiting, worsening headache, confusion, or loss of consciousness. A single episode after a head bump with an otherwise well child is less worrying, but repeated vomiting after head injury warrants urgent medical assessment. Also seek care for a baby under 6 months with any vomiting, severe abdominal pain, a stiff neck with fever, or a child who seems increasingly drowsy, irritable, or hard to wake - these can point to more serious infections needing prompt evaluation.