UKH

Question? Does anyone know the effect of a build up of sanitizer on rack and ropes? 

Yes. None.

If you are using it properly you should allow it to evaporate after rubbing your hands in it and before carrying on.

Depends what's in it, presumably. Metolius have recently added a note when landing on their website warning against alcohol (and other chemicals) on climbing equipment:

https://www.metoliusclimbing.com/

Guidance from manufacturers is inconsistent. A quick skim of the link below reveals that petzl gear can be washed at 60 degrees c whereas dmm gear is limited to 30 degrees. Logos clearly make all the difference. 

https://www.papertrail.io/blog/covid-19-links-and-resources-for-equipment-o...

Beal recommend that their ropes can be sanitized by soaking them in Isopropyl Alcohol for 30 to 60 seconds,so I can not see it being a problem. 

Few more manufacturer links in this discussion:

https://www.ukhillwalking.com/forums/rocktalk/is_hand_sanitiser_safe_on_our_ki...

But as Presley mentions, the guidance is somewhat inconsistent between diff. manufacturers regarding alcohol based ones. Just don't use bleach

Thanks everyone for your input. As mentioned manufacturers advice varies widely. I think I'll err on the side of caution and limit use of sanitizer but not get paranoid about it.