This is an excerpt from a member of another group I'm with and, although she lives in the USA, it's the same here in the UK.
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"I thought I possibly should post a warning about dangerous substances found in O2 cannulas.
I found that O2 supplies can contain dangerous chemicals, check your labels on your cannulas and make sure they don't contain DEHP or have an upside down triangle with the letters PHT inside the triangle.
PHT stands for phthalate which are very toxic and DEHP is a hormone interrupter amongst other things. I've found that they off gas and cause breathing problems, so check your tubing labels on your supplies and make sure they have a label that says contains no DEHP. if it doesn't have DEHP it won't have PHT.
They make my skin, mouth and throat burn, too.
It's not stamped on the tubing but you will find it on the insert in the packaging. If DEHP isn't in the tubing the insert will state that."
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My local hospital respiratory team didn't know about this (before today!) and my cannulae contain phthalates according to the label. I've asked my supplier to provide non toxic replacements.