Crying is a baby’s primary way of communicating, and in that sense it serves an essential purpose. But the old idea that “crying is good for a baby’s lungs” or that letting a baby cry freely builds character has no scientific support. Normal crying is healthy and expected. Prolonged, unsoothed crying is not beneficial and can become harmful.
Why Babies Cry
Before a baby can point, gesture, or speak, crying is the only tool they have to signal a need. Different cries carry different messages, and most parents learn to distinguish them within weeks. A hunger cry tends to be rhythmic and repetitive, escalating quickly if the baby isn’t fed. A tired cry is whiny and nasal, starting slowly and building. A pain cry is unmistakable: loud, sudden, high-pitched, and alarming.
Crying also triggers a biological response in caregivers. Research funded by the National Institutes of Health found that hearing an infant cry increases oxytocin release in the mother’s brain, activating circuits that drive comforting behavior like picking the baby up and soothing them. In other words, crying is designed to pull a caregiver closer, not to be ignored.
The Normal Crying Timeline
All babies go through a predictable phase of increased crying that pediatricians call the Period of PURPLE Crying. It typically starts around 2 weeks of age and peaks during the second month, then tapers off by 3 to 5 months. During this window, it’s not unusual for a baby to cry five hours a day or more, often in the late afternoon and evening, for no identifiable reason.
This crying pattern is a normal part of development, not a sign that something is wrong. It occurs in babies across all cultures and caregiving styles. The challenge is that it overlaps with the period when parents are most sleep-deprived and vulnerable to frustration, which is why understanding it as a temporary phase matters so much.
When crying exceeds three hours a day, more than three days a week, for longer than three weeks, clinicians may diagnose colic. Even colic, though exhausting for families, is not considered dangerous to the baby and resolves on its own.
What About the “Crying Strengthens Lungs” Claim?
This is one of the most persistent pieces of parenting folklore, and it’s false. Kaiser Permanente’s guidance states it plainly: there is no proof that crying strengthens a newborn’s lungs, and babies who cry a lot don’t develop greater lung capacity than quieter ones. A newborn’s first cry after birth does help clear fluid from the airways and establish breathing, but that’s a one-time event, not an ongoing benefit of crying.
When Crying Becomes Harmful
The distinction that matters is between crying that gets a response and crying that doesn’t. When a baby cries and a caregiver picks them up, feeds them, or simply speaks in a soothing voice, the baby’s stress response activates briefly and then winds back down. This is what researchers call a tolerable stress response, and it’s actually healthy. It helps the baby’s nervous system learn to regulate itself.
The problem arises when crying goes unsoothed for extended periods, repeatedly. Harvard University’s Center on the Developing Child describes what happens when a child’s stress response stays activated at high levels without a supportive relationship to help calm it: the protective response becomes toxic. Sustained high cortisol levels can impair the development of neural connections, particularly in brain areas responsible for language, attention, and decision-making. Over time, this “toxic stress” can affect learning, health, and well-being across a lifetime.
This doesn’t mean every moment of crying causes brain damage. Brief periods of fussiness, even ones where the baby cries for a few minutes before being soothed, are normal and harmless. The concern is with chronic, prolonged distress that no one addresses.
Crying and Sleep Training
Many parents wonder whether it’s okay to let a baby cry during sleep training. The American Academy of Pediatrics’ 2025 guidance draws a clear line: always respond to a crying baby, but normal fussiness is different from distressed crying. Their recommendation is to place your baby in the crib drowsy but awake, starting around 2 months old, and allow 10 to 20 minutes of restlessness and fussiness as the baby learns to fall asleep independently. That brief period of fussing is normal.
The AAP also notes that formal sleep training is not expected or encouraged at 2 months. At that age, the goal is simply establishing routines. The key skill babies eventually develop is self-soothing, the ability to settle themselves back to sleep without a parent’s intervention each time. Good sleepers learn this gradually, not through being left to cry in distress.
The Impact on Caregivers
A baby’s cry doesn’t just affect the baby. Research on first-time mothers of 3- to 4-month-olds found that mothers with higher cortisol levels (a marker of chronic stress) showed reduced brain activation when hearing their infant cry, particularly in areas involved in auditory processing and motor planning. Those same mothers were more likely to display intrusive parenting behaviors. In simple terms, when a parent is chronically stressed, their brain becomes less responsive to the baby’s signals, which can create a difficult cycle.
This is why support for caregivers matters as much as responding to the baby. A parent who is overwhelmed by persistent crying is more likely to respond in ways that aren’t helpful, or to stop responding altogether. If your baby’s crying feels unbearable, putting them safely in their crib and stepping away for a few minutes to collect yourself is a legitimate and recommended strategy.
When Crying Signals a Problem
Most crying is normal communication. But certain patterns should prompt a call to your pediatrician or a trip to the emergency room:
- Sudden onset of intense, persistent crying in a baby who was previously calm, especially if paired with drawing the legs up (which can signal abdominal issues like an intestinal blockage)
- A high-pitched, unusual cry that sounds different from the baby’s normal range
- Fever, vomiting, or refusal to eat alongside increased crying
- Signs of pain when touched or moved, which may indicate injury or infection
- Poor weight gain or feeding difficulties combined with persistent fussiness
Clinicians also check for easily missed causes like a hair tourniquet (a strand of hair wrapped tightly around a finger or toe, cutting off circulation) or a scratch on the eye’s surface. Both cause sudden, unexplained crying and are easy to overlook at home.