Some schools of thought, including those of many parents, assert that letting a child cry is an important part of their learning and development. However, it's an issue with many different degrees of point of view, and the answer to how long to let a baby cry can vary based both on the age of the baby, her individual personality, and the needs of your family as a whole. It's true that crying is normal and will not hurt your baby, but babies generally cry to communicate needs, so ignoring a cry can mean ignoring a need for food, a diaper change, burping, or just comfort, and in extreme cases, babies left crying for long periods of time can suffer from issues with insecurity and neglect. Newborns do not cry to get attention, and paying attention to your baby's cries is an important step towards learning her needs and desires so you can avoid reaching the point where she is crying to begin with.
When your baby starts to cry, the first thing to do to try to comfort her is to address her obvious, physical needs. Make sure her diaper is clean and she is properly fed and burped, and then, if that doesn't help, consider whether she might be too hot or too cold, tired and ready to be soothed into a nap, bored and ready to play, or overstimulated and ready to go somewhere less interesting so she doesn't feel so overwhelmed. If you still have trouble figuring out why your baby is crying, or how to help, it could be that you and your baby just don't have the language to communicate what the problem is yet, but that doesn't mean there aren't a few other things you can try to soothe or distract her into a hopefully quieter, happier state of mind. Potential solutions then include white noise or music, rocking or walking with her, skin to skin contact, swaddling, and even driving in a car. If your baby is crying constantly, check with the doctor to make sure nothing is physically wrong. Crying could also be a sign of an underlying health issue, like a milk allergy, formula intolerance, constipation, or acid reflux.
Newborns need to have their cries answered right away, but by 5 or 6 months, as they're starting to get more mobile, and to experiment with the beginnings of language and communication, many babies are ready to start learning self-soothe. Many parents begin to pause before responding, or allow children to cry during bedtime without running to their sides around this age to teach children to sleep on their own. Even using this method, many suggest that babies should not be allowed to cry for more than 10 minutes without your attention.
It’s your decision how to choose to handle your baby’s crying, but remember that she doesn’t cry for the sake of crying - she needs your help!