Burning waste on bonfire night can have a 'lasting impact' on the environment, Natural Resources Wales (NRW) warns.
They say a small minority use Bonfire Night to burn waste items such as tyres, treated wood, plastic, fuels, metal and glass which can impact on both the environment and people's health.
Jasmine Sharp, Duty tactical manager for Natural Resources Wales, said burning the wrong sort of material can also have an affect on people's health.
Duty tactical manager for Natural Resources Wales, Jasmine Sharp, said: "if you're burning the wrong sort of material, that can cause pollution to the environment and in terms of health impacts, burning waste can release harmful gases and that can have an environmental impact.
"But also it causes health issues to those who are breathing in polluted air and particularly for people who've already got respiratory problems.
"It's a small minority who are burning inappropriate materials, but most people are trying to do the right thing and part of the messaging that we're trying to get across is that for those people who don't necessarily know, and I think some people don't know and don't realise that what they're burning might have an affect on the environment and an affect on other people's health, just to let those people know that that could happen and what sort of materials they should be burning."
What can you burn?
NRW say if people are having bonfires, dry garden waste, untreated wood/timber and small amounts of leaves are appropriate to burn.
She added that people should also consider the dangers bonfires pose to wildlife, saying: "Hopefully people are aware of the dangers to wildlife, particularly hedgehogs making use of piled up materials in order to make somewhere to live or to hibernate, so just to remind people before you burn something, check there's nothing inside."