Parents of children with asthma often get it wrong when trying to clear their home of substances that can trigger an attack, a study suggests.
Each child will have different triggers for their asthma
Researchers at the University of Michigan team say some parents do too much while others don't do enough.
They cited the example of parents who buy a new mattress to ward off dustmites but then fail to shut windows to keep pollen out.
The study is published in the Journal of Allergy and Clinical Immunology.
The researchers interviewed parents of 896 children with asthma.
They found that only half of the 1,788 asthma-proofing steps taken by the parents were likely to work.
The others were unproven, unlikely to be helpful against the child's individual triggers, or, in a few cases, potentially harmful.
Parents most commonly reported taking steps to control their child's exposure to dust, dust mites and animals, and many said they were using special filters on ventilation systems and vacuum cleaners.
All are generally recognised as beneficial.
But parents also took steps that would not necessarily work for their child while overlooking others that would.
For example, a quarter of parents said that someone in the same household as the asthmatic child smoked, but did not report that there had been any effort to address this issue, even though tobacco smoke is a major trigger for asthma attacks.
A handful of the steps parents were taking were potentially harmful, such as the use of a humidifier in the room of a child whose triggers include house dust mites.
House dust mites thrive in humid environments, and using a dehumidifier is a more appropriate strategy.
The researchers say their findings indicate that doctors and other healthcare staff should ensure they educate parents about what exactly what might be triggering their child's asthma symptoms and attacks.
They also say parents should be instructed about the most effective steps they can take to reduce their child's exposure to those substances.
University of Michigan paediatrician Michael Cabana, who led the research, said: "Eighty percent of parents in this study knew at least one specific factor that triggered their child's asthma symptoms, and 82% of those had devoted some effort to help their children avoid these triggers.
"But we also found that a lot of parents were pursuing strategies that haven't been endorsed by national guidelines or aren't likely to be helpful given their child's particular triggers."
He added: "Parents are dedicated and eager to do something to help their kids.
"As physicians, we need to do a better job of providing information and balancing the messages they may hear elsewhere, so parents can do what's proven to prevent asthma symptoms and attacks."
The researchers found education about a child's asthma was effective.
Parents who had received some education or whose children had seen a doctor regularly were more likely to have taken steps to protect their children from asthma triggers.
A spokeswoman for the charity Asthma UK told BBC News Online: "In the UK over 40% of parents of children with asthma in the UK say they would like more information from their family doctor.
"They end up sifting through vast amounts of information themselves which may or may not be helpful. Parents need an impartial expert view, ideally from their GP or asthma nurse.
"Parents and children with asthma should be having regular asthma reviews with their health professional so they can discuss the best ways to avoid their child's asthma triggers and gain better control over their asthma."