Poor housing conditions are contributing to the high levels of asthma in children in Wales, a report says.
Unsatisfactory housing causes many health problems, experts say
Shelter Cymru says people who have breathing problems are more than twice as likely to be living in damp houses.
Respiratory symptoms are more prevalent, as are headaches and fevers.
John Puzey, director of Shelter Cymru, said it was no co-incidence that Wales had poor housing and one of the highest rates of asthma in the world.
Shelter Cymru estimates that 50,000 children are living in unfit housing in Wales.
The Global Initiative for Asthma (GINA) estimates that 33% of children in Wales suffer asthma symptoms - more than three times the levels in Spain, Poland and Denmark.
"The links between poor housing, homelessness and poor health are so obvious, but they often seem overlooked when it comes to resources," Mr Puzey said.
"We estimate the cost of poor housing to the Welsh NHS is at least £50m a year.
"We need more investment in housing in Wales and we are calling for a new fund to resource housing and health-related action research.
"This will ensure that new investment can be targeted at the most cost-effective way of tackling poor housing to improve health.
"Housing needs to be recognised as one of the major causes of the asthma epidemic."
The report, Housing and the asthma epidemic in Wales, was released as Shelter Cymru's annual conference began in Swansea.
Earlier this year, Shelter Scotland revealed that poor housing was affecting the health and education of many children and it urged the Scottish Executive to do more to address the situation.
The call came as part of the Shelter's UK-wide Million Children Campaign.
Liz Nicholson, director of Shelter Scotland, said children were the hidden victims of the UK's housing problems.
Shelter also said that one in 12 children in the UK are more likely to develop diseases such as bronchitis or asthma because of bad housing.