Newborn babies who look more like their dads than mum are usually healthier a year later, new research has found.
It's because fathers are more likely to be certain the child is theirs.
The findings come from the long-running Fragile Family and Child Wellbeing study in the US, looking at the health and lives of nearly 5000 children born between 1998 and 2000 to low-income and unmarried parents.
"Fathers are important in raising a child, and it manifests itself in the health of the child," co-author and State University of New York professor Solomon Polachek told the Wall Street Journal.
The study focused on 715 families in which the baby lived with only the mother.
If a father thought their baby resembled them, they spent on average 2.5 more days every month involved in their child's upbringing than those who didn't feel the same connection, the research found.
This resulted in a 10 to 25 percent fewer emergency room visits, asthma and incidences of illness.
"Those fathers that perceive looking like the baby spend more time with the baby and are more certain if the baby is his," said Dr Polachek.
"Because women do not need facial resemblance cues to decide whether to provide care, we expect baby looks affect child developmental outcomes only through a father's investments."
Previous research has found absent fathers are less inclined to get involved in their children's lives if they are poor in health, which the new study aimed to account for.
The research backs a growing body of evidence that fathers are more likely to help with a child's upbringing if they're convinced the baby is theirs. A previous study in Senegal, focusing on polygamous families, found fathers spend more time with children who look and smell like themselves, the Journal reported.