From a hygiene perspective only, is there anything wrong with a couple sharing underwear?

We were out with friends last night and a couple (we’re all some flavor of LGBT, this couple is two women) mentioned they share underwear and socks. Obviously there is some social stigma around it, but is there anything actually unhygienic about this practice? They obviously wash them between uses. I didn’t think it was a massive deal although not my cup of tea but others were disgusted.