Parents who go through a bitter divorce could permanently damage their child's health, a study shows.
Children whose parents stay on speaking terms after a split are far less prone to falling ill in later life, researchers say.
But those whose parents cut off contact are far more likely to suffer from a weak immune system even decades later.
And experts believe youngsters' health is damaged by the stress of growing up in a broken home that it might explain rising rates of asthma and heart disease among those who experienced it.
Previous research has found that adults whose parents split up were more likely to suffer mental health problems and troubled relationships of their own.
More than 100,000 people a year divorce in England and Wales, around half of whom have at least one child. However, the nature of the divorce appears to be significant. Children of amicable separations had no greater risk of getting ill than those whose parents had stayed together, the latest research found.
Dr Michael Murphy, lead author of the study, from Carnegie Mellon University in Pennsylvania, said: "Early life stressful experiences do something to our physiology and inflammatory processes that increase risk for poorer health and chronic illness.
"This work is a step forward in our understanding of how family stress during childhood may influence a child's susceptibility to disease 20 to 40 years later."
For the study, 201 healthy adults 118 men and 83 women were quarantined in a hotel and given nasal drops containing rhinovirus, which causes the common cold. Over five days of monitoring, 149 participants showed signs of infection, of whom 60 developed a full-blown cold.
Those whose parents lived apart and never spoke were three times more likely to get the cold. While adults whose mother and father remained on good terms after splitting showed no difference to people with intact families. This suggests extreme childhood stress changes the body's response to the threat of illness.
It may also cause a surge in inflammation in the body, linked to asthma, cancer and heart disease all previously reported at higher rates in children of separation. Products of broken homes are also more likely to suffer premature death, previous studies have found.
The latest, published in journal Proceedings of the National Academy of Sciences, suggests acrimony' between parents may be to blame, while co-operation means children suffer less trauma.
Co-author Sheldon Cohen, professor of psychology at Carnegie Mellon University, said: Our results target the immune system as an important carrier of the long-term negative impact of early family conflict.
"They also suggest that all divorces are not equal, with continued communication between parents buffering deleterious effects of separation on the health trajectories of the children."