How do I remove stubborn soap scum from a glass shower door? which products really work?

CLR and/or vinegar (the white kind not the other types).

CLR or white vinegar will clean it. To P R E V E N T it from recuring buy a bath squeegee and squeegee the glass after showering. Much easier than cleaning.

Are you sure its just soap scum? It could be limescale, which you can get specialist cleaners for, but vinegar works quite well.

cerium oxide

it is used by window companies in cleaning dirt from glass and vinyl

Thanks everyone for your input. I will be trying your suggestions.

CLR

I use dish detergent with 1capful of cloudy ammonia

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White Vinegar or Eucalyptus oil with a scourer do a fantastic job.

I like to use Murphy's Oil soap on a green mesh scrub pad( full strength). works with minimum elbow grease and smells good too.

Clr

CLR works on most stains