Babies can become unwell quickly, and they cannot tell you what is wrong, so recognising warning signs is key. Red flags that warrant urgent assessment include being unusually sleepy or difficult to wake, a weak, high-pitched, or continuous cry, fast or labored breathing, pauses in breathing, a bulging or sunken soft spot, a non-fading rash, a fever in a baby under 3 months, or being unusually floppy.
Also concerning are feeding much less than usual, far fewer wet nappies, repeated vomiting (especially green vomit), cold or mottled skin, or a baby who simply seems very different from normal. Pale, blue, or grey skin or lips needs an emergency response.
Call your local emergency number for any of the most serious signs above, and contact a doctor promptly for the rest. Parents often sense when something is wrong before clear signs appear, and that instinct is a valid reason to seek help. It is always better to have a baby checked and reassured.