While your baby is born with a mechanism to block out sights and sounds around them to ensure they get enough sleep and nourishment, this mechanism disappears around 1 month old. That’s why colic usually begins at 3 or 4 weeks old. Think about it, your baby just spent close to a year safely inside the womb. The outside world is full of new sounds, lights, sensations, and people - it’s easy for your baby to feel overwhelmed and overstimulated. They release that stress by crying (a lot.).