It’s no secret that babies are extremely sensitive to their surroundings. From the time they are in the womb up until their first few years of life, infants rely heavily on their senses to understand the world around them. One of the ways babies perceive their environment is through smell.
A baby’s sense of smell is incredibly powerful. Newborns can differentiate between the scent of their own mother compared to another woman. Infants are also able to detect changes in odor that signal emotional shifts in their caregivers. This has led researchers to wonder: can babies smell when someone close to them is stressed?
How Does Scent Relate to Stress?
Before examining if babies can detect stress specifically through scent, it helps to understand how our body odor changes when we are under stress. When a person experiences stress or anxiety, physiological changes occur throughout the body as part of the “fight or flight” response. This includes increased activity in the apocrine sweat glands, which produce a milky sweat that contains pheromones.
Pheromones are chemical signals that convey information from one individual to another of the same species. In humans, pheromones communicate a range of emotional states including fear, anxiety, and stress. These odorless chemicals are present throughout sweat and other bodily secretions, altering our normal scent profile when we are under duress.
Cortisol and Odor
One of the main drivers of pheromone production and changes to body odor during times of stress is the hormone cortisol. Cortisol is released as part of the body’s natural response to perceived threats. This steroid hormone prepares the body to deal with challenging or dangerous situations by suppressing non-essential functions and ramping up processes that provide energy and focus.
However, chronic stress and consistently high cortisol levels put the body into an imbalanced state. This can impact the types of proteins, lipids, and other molecules that are excreted through sweat. Researchers have found that the composition of sweat samples differs based on whether a person is stressed versus relaxed. Devices have even been created to “smell” cortisol levels through human skin odor.
Odor and Emotional Contagion
The ability to detect emotions like stress or anxiety through scent may be part of a phenomenon called emotional contagion. This is the process by which one person transmits their emotional state to another without conscious knowledge or effort. Studies have shown that humans can identify fear, disgust, happiness, and other feelings based on body odor samples.
It is believed scent provides a medium through which we can synchronize our emotions with others as a primal survival tactic. If someone smells fear, their instinct is to prepare for a threat. Likewise, the scent of happiness can put people more at ease. This synchrony helps regulate behaviors within groups and families.
The Power of an Infant’s Nose
Babies have incredibly sensitive noses compared to adults. An infant’s sense of smell begins developing in utero, with the olfactory nerves becoming functional as early as 11 weeks gestation. Newborns prefer the scent of their own amniotic fluid and breastmilk, demonstrating an ability to discern different smells right from birth.
After birth, babies continue perfecting their sniffing capabilities through breastfeeding. The nipple search required for latching exposes infants to a wide array of aromas that trigger neurological connections. By 3 months of age, babies have approximately 40 million olfactory receptor cells. For comparison, this is about 40 times more scent receptors than adults have.
Odor Preference and Aversion
Thanks to their super-sensitive noses, babies display distinct odor preferences and aversions:
- Newborns will turn toward the smell of breastmilk but show aversion to sour odors.
- Babies prefer the scent of their mother over others.
- Infants demonstrate liking for certain food smells like vanilla and onion early on.
- Foul odors like rotting eggs trigger negative responses in babies.
This ability to discern pleasant smells from offensive ones is crucial for infants to bond with caregivers and identify nourishment sources. Preferences and aversions also motivate attachment and avoidance behaviors that aid survival.
Sniffing Out Safety
Babies rely heavily on scent to assess safety and danger in their surroundings, especially related to caregivers. Infants as young as a few days old display a calming response to the odor of their mother’s breast pad or unwashed t-shirt. The smells of home and family members provide comfort.
Babies also exhibit fear, distaste, or unease when exposed to odors that signal unfamiliarity or possible threats. Strange smells cause hesitation, rather than relaxation and approach behaviors. This wariness helps motivate infants to seek proximity to their trusted caregivers when feeling insecure.
The Link Between Scent and Infant Stress
Given babies’ exceptional scent detection skills, it stands to reason they can smell stress hormones, pheromones, and other odor indicators that a caregiver or sibling is under stress. Although limited research exists in this area, initial findings suggest babies do indeed sniff out stress.
Impact of Maternal Stress Odor
In one study, the body odor of women experiencing psychosocial stress was collected on pads. When these odor samples were presented to other women, it activated regions of the brain involved in processing emotional cues and social information. This provides evidence that stress generates a distinct scent.
Researchers also observed the reactions of 2 to 6 month old infants to the smell of stress odor from their mothers versus neutral odor. The babies showed signs of wariness,displayed more sniffing behaviors, and had increased cortisol reactivity when exposed to the maternal stress scent.
Premature Infant Response
Premature babies in the NICU experience many unfamiliar smells, including medical odors that can induce stress. In one experiment with pre-term infants, exposure to the scent of maternal milk versus formula activated the reward center of the brain and resulted in more stable vital signs. The maternal odor had a calming effect.
Conversely, premature babies exposed to the scent of stressed mothers showed greater turned away, grimacing, and altered breathing. This suggests they detected and reacted to the stress odor even at an early stage of development.
Odor-Emotion Conditioning
From as early as a few days old, infants can learn to associate certain odors with positive or negative experiences. In one study, newborns were exposed to the scent of cherry mixed with smiles and affection from the researcher. The babies learned to connect the smell of cherry with happiness.
This demonstrates that babies have the capability to connect scents like maternal stress odor with the resulting behaviors or emotions they produce. If a mother’s anxiety smell consistently correlates with behaviors that make an infant feel insecure or distressed, the baby will likely learn to associate that odor with negativity.
How Infant Detect Stress Odor
Exactly how babies recognize and process scents associated with caregiver stress is still being investigated. However, researchers have some ideas about the pathways that enable infants to smell stress.
Brain Processing
Olfactory information is processed by the limbic system in the brain, specifically the amygdala and hippocampus. These areas handle emotion, mood, and memory. When babies smell their mother’s scent, it gets sent to these parts of the brain and associated with the comforting feelings created by her presence.
But if mother’s odor has been altered by cortisol, pheromones, and other stress chemicals, her scent may activate different neural pathways. Instead of signaling safety, the smell could trigger discomfort or wariness for babies as they process the information through the emotional centers of the brain.
Unconscious Sensing
It’s unlikely that babies consciously think “this is the smell of a stressed parent.” Their ability to detect and be impacted by stress odors appears to operate at an unconscious, instinctive level. Infants respond to the smell before they cognitively understand what it means.
Research shows even sleeping newborns reacted with distinct facial expressions and body movements when exposed to the odor of anxious versus happy women. Babies seem able to smell stress even if they don’t comprehend that’s what they’re sensing.
Innate vs. Learned
Scientists have debated whether babies’ perception of stress through scent is an innate ability or learned through experience. Since infants respond to maternal stress odor even at very young ages, it suggests they are born with some capability to detect these smells innately.
However, learning also plays a role as babies associate scents with emotional states and reactions during early development. Distressed maternal odor may become more salient for infants who regularly pair that scent with insensitive or frightening caregiver behaviors.
Impact of Smelling Stress on Babies
What happens when infants detect the smell of chronic stress or anxiety on their caregivers? Research indicates some concerning effects for baby’s health and development.
Physical Effects
When babies take in the odor of a stressed parent, it can trigger physical responses including:
- Increased heart rate
- Faster breathing
- Rising cortisol levels
- Decreased motor activity
- More spit up
- Poor sleep
These reactions divert the body’s resources away from growth and restoration. Chronic activation of the stress response due to sniffed-out maternal anxiety can be detrimental for infant’s fragile systems.
Behavioral Effects
In addition to physical reactions, babies may exhibit behavioral shifts in response to smelling stress on a caregiver:
- More crying and fussiness
- Increase in stress behaviors like arching away
- Less smiling, laughter, cooing
- Altered sleep-wake cycles
- Reduced motor coordination and play
These behavioral changes signal babies are unsettled due to sensing maternal stress odor. They may have more difficulty with self-regulation.
Brain Development
Experiencing chronic or traumatic stress in infancy has detrimental effects on brain development. Brains are shaped by experiences, especially within caregiving relationships early on. Consistently smelling maternal stress and activating baby’s own stress response can negatively impact:
- Neurological connections
- Cognitive functioning
- Language processing
- Sensory integration
- Emotional development
The architecture of the brain changes in response to persistent stress, making it more reactive and less resilient when facing challenges.
Relieving Stress Aromas for Babies
Since maternal stress odor can be taxing for infants, actively reducing these smells may help lower baby’s stress levels. Here are some tips for minimizing stress aromas in babies’ environments:
Aromatherapy
Introducing calming scents into the home and on clothing can help mask stress odors while also encouraging relaxation. Some aromatherapy options include:
- Lavender – Soothes the nervous system
- Chamomile – Reduces anxiety
- Ylang ylang – Promotes comfort and joy
- Rose or vanilla – Pleasant, attractive aromas for babies
Reduce Triggers
Minimizing sources of stress in a parent’s life can help lower cortisol and anxious pheromone production. Practicing self-care, getting support, and managing daily pressures can keep odor triggers to a minimum.
Clean Clothes
Laundering clothes and linens frequently eliminates sweat, which carries stress odors. Dressing baby in freshly washed garments can provide comforting, neutral scents.
Fresh Air
Opening windows regularly refreshes stale indoor air and keeps circulating new oxygen. This prevents stress smells from building up in closed quarters.
Showering
Bathing and showering removes sweat and other particles carrying scents. If a mother feels tense, washing up before holding her baby may prevent transferring stress odors.
Improving Detection Understanding
While research indicates babies can smell stress, there is still much to learn about infants’ incredible olfactory capabilities and how odor exposure impacts development. Moving forward, areas to focus on include:
Early Intervention
Developing interventions that target mother-child interactions and limiting stress aromas in babies’ environments. These approaches may buffer infants from adverse effects.
Mechanism Research
Exploring exact mechanism by which babies detect stress through scent, including innate neurobehavioral pathways.
Long-Term Outcomes
Tracking if stress odor exposure in infancy correlates with physical, neurological or psychological outcomes later in childhood.
Variation Factors
Investigating how infants’ sensitivity and reactions to stress smells may differ based on factors like gender, environment, and culture.
Mitigation Strategies
Identifying best practices for improving family functioning, reducing parental stress, and encouraging positive mother-child interactions to avoid transmitting stress odors.
Conclusion
Babies have an incredible sense of smell, allowing them to detect emotional states like stress or anxiety. While limited research exists, initial findings indicate infants can smell stress hormones, pheromones, and odor changes in the scent of their caregivers. Detecting maternal stress aromas causes physical, behavioral, and developmental effects for babies.
However, further exploration is needed to fully understand babies’ scent detection capabilities and outcomes. Focusing on protective interventions and improving emotional connections has the potential to limit babies’ smelling of chronic stress.