This is a great question because, after all, if an infant is in pain, they are very likely to cry. So, if they cry—especially for long periods of time—how do I know it’s not because of pain?
Again, there are a number of reasons to know that this crying—especially this pattern of crying over weeks and months—is not due to pain. But before discussing some of those, let’s make an important point about the role of your health care provider in helping you decide this. It is true that infants can cry for long periods of time when they have a disease or are sick. Usually, whatever crying they might do because of the sickness is “on top” of the normal increased and decreased crying that was described before. But that is, of course, very difficult for parents to know. This is why it is always appropriate to take your baby to your health care provider to be examined for signs of illness. They may well do a couple of simple tests that help them decide whether there is an associated illness. It will help them to know whether, in addition to crying, your infant has other symptoms indicating that he or she may be sick, including diarrhea (frequent, loose, wet stools), weight loss (especially over weeks, rather than just for a day or two), or a temperature. Finally, it is sometimes the case that infants whose crying is always high-pitched (some people say ‘screaming’), who regularly arch their backs when they cry, and whose crying is not worse during the late afternoon and evening hours are more likely, but not necessarily, to have a sickness contributing to their crying. So, it is always appropriate for your health care provider to assess an infant who is crying a lot to see if there is an illness contributing to the crying.
“If you believe your baby may be ill, it is important to get them checked by a health care provider”
However, even in infants with no illness (about 98%), how do we know that these infants are not in pain. An important reason relates to what we have already described: if these features of crying were manifestations of pain, then we would have to accept that essentially all infants the world over, regardless of culture, are in pain for many hours for many weeks in the first months of life. It also would mean that other animal species who have similar distress curves would be in pain, and that premature infants were not in pain for the first couple of months, but then had weeks to months of pain after being well for six or eight weeks. None of this seems reasonable.
Another reason is that, even though infants can cry a lot, there are other times of the day when they are perfectly happy, cooing, giggling, and being wonderfully responsive. That is not the way most of us as adults feel when we are sick, and it is not likely to be true for infants either. And many mothers experience this often very rapid change from being well and content at one moment to being in an all out cry a minute later. That is not the way sick people act, whether they are adults or infants.
One of the differences to keep in mind here is that, as described previously, we are not talking about a single, acute episode of prolonged crying. For any particular such crying time, it is very difficult to tell whether an infant is in pain or just crying. One of the important keys here is we are describing increased crying in infants that usually begins in the first couple of weeks of life, that tends to occur in the late afternoon and evening, that increases over weeks before it reaches a peak, and so on. This is prolonged crying over prolonged periods of time, not a single acute crying time. It is that pattern of crying that is not due to pain.
A very helpful study indicated another reason why we are sure this increased early infant crying is not a manifestation of pain. This study showed that what made high crying infants (that is, those who met criteria for ‘colic’— see next section for a description of colic) cry so much compared to infants without ‘colic’ was not that they were in more physical distress, but that they were crying more loudly and intensely in response to the same stress and mildly painful stimulus (namely, a typical physical examination that would occur in a doctor’s office). In other words, for the same stimulus and the same physiological (or physical) stress, some babies cry more and longer, but not because they are in more pain or more stress.
“The study showed that what made high crying infants cry so much, was not physical distress,
but rather that the infant was crying more loudly and intensely”
Finally, if this prolonged crying really was an indication of disease, then it would make sense that at least some of these infants would still be sick and that they would be discovered to be sick later in life. But for infants that do have this increasing and decreasing pattern of crying, there is no evidence that they have illnesses later in life (unless, as previously mentioned, they have been shaken or abused). Some infants, who have high crying when they are over six months of age, may be at risk for having illnesses or other concerns later, but this is not true of early increased crying.