It is entirely normal for infants to cry without any apparent reason, and most healthy infants go through this phase.
The “Period of PURPLE Crying” was developed by the National Center on Shaken Baby Syndrome for the purpose of educating parents about the normalcy of infant crying and the dangers of shaking an infant.
PURPLE is an acronym for:
Peak of crying
The worst crying tends to occur around two months of age and declines from three to five months.
The crying often comes on and stops for no apparent reason.
The baby is often difficult to soothe.
The baby may appear to be in pain even if they are not.
The crying may go on for several hours a day.
The baby often cries more in the late afternoon or evening