Most parents know that their mood affects their children. If a parent is anxious, irritable, absent or emotionally unavailable, children usually notice. What is less well known is that this influence does not happen only at a behavioural or emotional level. It also happens biologically, in the body.
In recent years, a growing number of studies measuring stress hormones in parents and children simultaneously have shown that there is a measurable physiological connection between them. Levels of cortisol — the main stress hormone — often appear to move in a synchronised way. When stress rises in parents, corresponding changes are observed in children’s cortisol levels, even when no one has any conscious awareness that this is happening. A child may appear to be playing or absorbed in something else, but if the parent in the same room is experiencing stress, the child registers it bodily.
This finding has been recorded even in infants of six months. In other words, long before children can verbally understand what is happening around them, their bodies appear to respond to the physiology of the people caring for them.
This is why we often say that many emotional states are registered first by our body and only later understood cognitively. Bodily sensations and the systems that detect safety or threat develop much earlier than the cognitive capacities that allow us to explain in words what is happening inside us.
The parent as a reference point for safety
Attachment theory offers an important framework for understanding these findings. Children are not simply sensitive to their parents’ state because they live with them. Their brains are evolutionarily organised to use the parent as a primary source of safety and as a regulator of their emotions.
When a parent is available, responds to the child’s needs and can soothe them when they are struggling, the child’s nervous system receives the message that the world is safe enough. Conversely, when a parent is constantly overwhelmed, anxious, unpredictable or emotionally absent, the child may begin to operate as though there were danger, even when there is no objective threat in the environment.
In this sense, a sense of safety is not only a psychological experience. It is also a biological state of the nervous system.
How children “read” their parents
Children do not react only to the events happening around them. They often react to the way their parents react to those events.
Psychologists describe this process as social referencing. From a very young age, children look at their parents’ face, tone of voice and body posture in order to work out whether a situation is safe or dangerous.
An infant faced with something unfamiliar often turns first towards the parent. If they see fear, hesitation or panic, they tend to stop. If they see calm, interest or confidence, they are more likely to explore. In other words, children use their parents as a kind of “biological compass” for interpreting the world and for judging which situations are safe and which are not.
Why does this happen?
In childhood, the brain system that regulates the stress response is still developing. Children are not born with a fully developed capacity for emotional self-regulation. Before they can regulate their own emotions and physiology, they rely on co-regulation with their parents or caregivers.
This is not a problem or a weakness. It is part of the normal developmental design of the human being. The child “borrows” the adult’s regulatory capacity until they gradually develop their own.
This is why the process of co-regulation is at once emotional and biological. The child’s nervous system continually monitors and scans its environment, and particularly the people on whom its safety depends.
Stress is transmitted — but so is regulation
A review of 55 studies on family stress and the biological synchrony between parents and children found that higher levels of parental stress are systematically associated with disruptions in the physiological synchrony of stress systems within the family.
The same field of research, however, also offers a particularly hopeful message.
Studies show that when families face a stressor together and the parent can recognise and name what is happening, children’s stress levels often decrease. It does not appear to be the absence of difficulties that protects children, but the way parents handle difficulties within the relationship.
Parents with a greater capacity for emotional regulation tend to show better physiological synchrony with their children. Emotional regulation does not mean never being anxious or staying constantly calm. It means being able to recognise one’s stress, to stay in contact with it without being flooded, and to try to process it rather than remaining permanently activated.
This capacity appears to be directly connected with how effectively children develop their own mechanisms for managing stress.
When stress stays invisible and unspoken
Many parents try to protect their children by hiding their anxiety or their difficulties. Children, however, often sense that something is going on, even when they do not know exactly what it is.
When a parent carries intense stress without recognising it or communicating it in a way appropriate to the child’s age, the child may be exposed to the consequences of that activation without having any framework for understanding it or any possibility of co-regulation.
By contrast, when a parent can say something like: “I’ve had a difficult day and I feel under pressure, but I’m working on it”, they offer the child far more than an explanation. They offer a model. They show that stress is real, but also manageable.
What matters here is not disclosing every difficulty to a child. It is the presence of an adult who can recognise, bear and process what they are going through.
Stress is not the problem. Chronic, unprocessed stress is
An important clarification is needed at this point.
The fact that children are biologically affected by their parents’ stress does not mean that every difficult day or every period of pressure damages their development.
Stress is a normal part of life and of development. Children need experiences of challenge, frustration and difficulty in order to develop emotional resilience.
What appears to burden the developing stress system most is not isolated difficult experiences, but repeated patterns of chronic, intense and unprocessed stress — particularly when the child has no access to an available adult who can act as a source of safety and co-regulation.
The relationship as a protective factor
Research shows that the quality of the parent–child relationship functions as an important protective factor against the effects of stress.
A 2024 study showed that a warm and supportive relationship can reduce the impact of parental stress on the child’s stress physiology, even when parents’ stress levels are high.
This means that stress alone does not determine the outcome. What also plays a decisive role is whether the child experiences the parent as available, emotionally present and willing to restore the emotional connection when it is disrupted.
Repair after a difficult moment, emotional availability and warmth are not merely “good parenting practices”. They appear to serve an important biological function in children’s development.
The power of repair
One of the most important findings in developmental psychology is that children do not need perfect parents.
Healthy emotional development is not based on the absence of ruptures. It is based on their repair.
What appears to benefit children most is not growing up beside a parent who never struggles, but beside a parent who can bear struggling, can recognise what is happening, and can gradually find the way back to regulation.
Children do not learn only from their parents’ calm. They learn by watching how their parents face difficulties, how they perceive and process their feelings, how they ask for support and how they recover after a period of pressure.
In this sense, the most valuable lesson for children is not that stress should be avoided. It is that we can recognise it, manage it, bear it and regulate it within relationships.
Children do not need to grow up beside people who are untouched by anything and never buckle. They need to grow up beside people who show them that when we do buckle, we can also come back.
