Neonatal hypothermia and signs of cold stress in the newborn and infant

Newborns and infants are a population that is particularly vulnerable to temperature fluctuations and cold stress, especially during the winter months. Their thermoregulatory physiology is still immature: limited muscle mass, low energy reserves, and a high body-surface-area-to-weight ratio promote rapid heat loss.

In the first months of life, any prolonged exposure to environmental temperatures below the thermoneutral zone can lead to hypothermia, with possible metabolic, neurological, and cardiovascular consequences. Prevention requires a solid understanding of signs of cold stress, environmental factors, and thermal protection strategies, both indoors and outdoors.

Pathophysiology of cold stress

Neonatal hypothermia develops when endogenous heat production fails to compensate for heat loss. In newborns, the reduced ability to generate heat through muscle shivering—together with an immature peripheral vasomotor response—increases susceptibility to heat loss. Heat dissipates through conduction (contact with cold surfaces), convection (cold air), evaporation (moisture on the skin), and radiation.

Rapid exposure to very different temperatures—such as moving from a heated environment to cold outdoor spaces—represents an acute thermal stress that can quickly destabilize neonatal homeostasis. Physiological effects include increased heart rate, increased basal metabolic rate, accelerated mobilization of energy reserves, and reduced peripheral perfusion. In more severe cases, lethargy, apnea, hypoglycemia, and impaired renal function may occur.

Clinical signs of cold stress

Early recognition of cold stress signs is crucial to prevent hypothermia.

Newborns and infants may show:

• Skin signs: cold extremities, paleness or peripheral cyanosis, mottled skin, pale lips and face.
• Behavioral signs: irritability, high-pitched crying, reduced motor activity, a posture with limbs flexed close to the trunk to reduce heat loss.
• Physiological signs: compensatory tachycardia, tachypnea, hypotonia or lethargy in more advanced cases.

By contrast, signs of thermal comfort include an even complexion, skin warm to the touch, coordinated motor activity, normal muscle tone, and effective sucking. The supine position of the newborn or infant in the crib, cradle, or in a generously sized stroller/pram with the limbs semi-flexed is an adaptive behavior that helps conserve energy and reduce heat loss.

Indoor environmental factors

Home conditions significantly influence an infant’s thermoregulation. Temperatures below 20°C or direct drafts may increase the risk of cold stress in winter, while overly warm environments or high relative humidity (>60%) can compromise the ability of older infants to adapt thermally.

Other factors to consider include:

• Cold floors or uninsulated surfaces (ceramic, marble) in contact with the baby.
• Poor insulation of doors and windows, which promotes heat loss.
• Inadequate clothing and fabrics: non-breathable synthetic materials can hinder heat regulation.

Layering clothing is the most effective strategy to modulate body heat. Multiple thin, breathable layers make it easier to add or remove garments depending on ambient temperature, reducing the risk of hypothermia.

Outdoor environmental factors

Winter outdoor exposure adds further risk. Drafts, wind, rain, and low temperatures increase heat loss—especially from the head, which is a major area for thermal dispersion.

Temperature swings—such as moving from a warm indoor environment to harsh outdoor conditions—are an additional stress: the body must rapidly activate vasoconstriction mechanisms and increase energy expenditure, but this response is immature in newborns. This can lead to irritability, decreased sucking, reduced activity, and greater susceptibility to respiratory infections.

Preventive strategies include:

• Avoiding prolonged outdoor exposure during the coldest hours of the day.
• Using winter footmuffs for prams and strollers, windproof covers, or breathable protective covers.
• Limiting abrupt transitions from warm environments to cold outdoor spaces, favoring gradual adaptation.

Cold stress in newborns and infants is a preventable thermal emergency. Understanding the pathophysiology, recognizing clinical signs early, carefully managing indoor and outdoor environments, and adopting effective layering strategies are essential to ensure optimal thermal comfort and reduce the risk of complications. Thermal protection during the winter months is a central element of pediatric care, both at home and in hospital settings.