Just read up on it. Can also be triggered by infections or mold. Another reason why it’s wrong that so many young families seem to live in badly maintained rental properties.
Re mould, IMO it’s high time there was compulsory registration of all LLs* and regular official inspections of all rental properties - with really hefty fines for landlords who neglect maintenance. I’d go so far as to say that properties of repeat offenders should be confiscated. I say that as a LL myself.
*might add that I’m pretty sure (from reliable anecdotal evidence) that a good many LLs don’t declare their rental income, so compulsory registration might just result in a bigger tax return. If you don’t have a mortgage and you don’t use a letting agent, in many parts of the U.K. there is literally nobody you have to inform that you are renting out a property. The self assessment tax form doesn’t ask for addresses, only how many properties.
And I dare say many of the worst-neglected properties are owned by slumlords who pack vulnerable people into sub standard accommodation and demand the rent cash in hand.