Just read a post on Reddit (r/NBE), that evidently came from a post on Breast Nexus.  The gist was that prior to massaging in any transdermal items to the breasts, you should first clean the nipples with an alcohol wipe, as this will get rid of any plugs or deposits that could affect absorption--no need to clean the entire breast, just the nipple (I assume also areola area).  The poster was mainly talking about massaging in flaxseed oil, but also mentioned other items.

Any thoughts on whether this is necessary or not?

I have no idea if it will work or not, but alcohol to me would dry nipples out. That sounds like it would hurt.

Agree, but as soon as they are cleaned, I'm immediately putting on transdermal creams or oil which I think would prevent any damage.

Of course, stripping off oils and unclogging pores would be advantageous when applying any product that you want to be fully absorbed.
That would apply to the entire breast, or any other patch of skin, as well as the nipple.
You don't have to use alcohol though. I think a shower would suffice, if that's convenient.

You could also use a remover that is not quite so aggressive as straight alcohol, maybe like witch hazel or a facial toner or just soap and water.
Sure, you should definitely re-apply some type of oil, lotion or moisturizer afterward to restore the balance.

Karen 

Thanks, Karen, I don't disagree.

I know that when I was lactating (around a year ago, I took Dom for 5 months and pumped so that I could induce lactation and increase breast volume and tissue, which it did, and so far I've kept the size increases), I would get milk blebs in my nipples that could be squeezed out kinda like whiteheads, but I've not really noticed them since I quit inducing--so not sure there would be anything blocking my nipples's channels or whatever...

The poster on Reddit mentioned she cleaned her nipples with alcohol and rest of her breasts with witch hazel, and the previous poster she quoted from BreastNexus was doing that also, and I did search for "alcohol" and for "witch hazel" on both sites and did get some hits for cleaning using them...

Below are links to the two posts:

https://www.reddit.com/r/nbe/comments/wvl1hu/heres_a_breakdown_of_my_process_and_how_i_grew/

https://www.breastnexus.com/showthread.php?tid=27859&highlight=clean+nipples+with+alcohol. (the second post mentions cleaning the nipples--I should mention that the poster, Miss Mad Scientist, has posted a LOT, and typically includes additional information on why she uses what she uses (reminds me of Lotus!)).