I have an eczema/psoriasis patch at the top my arms. Its dry skin with a dark-redish colour. The eczema is not too severe and the patches are not too large BUT they are noticeable.
To be honest, its never been a problem for me. If a girl does ask just tell her its eczema or tell her its dry skin, depending on how severe your condition is (psoriasis is too technical and most people won't know what you mean by it. Using the word psoriasis will just freak her out and confuse her). Chances are she'll know what eczema is and it won't be an issue for her.
And as the other comments say
" if you are that worried then let them know you have some eczema when you book "
" Your money, your punt "
If your condition is severe or you are that worried then BEFORE handing over anything make sure she's ok with it. If she's not ok with it (check her reaction! and her tone of voice) then just walk out, at least u didn't loose anything.