focusing on future speciality in ur med application if passion for med stems from it?

I would categorically not mention this in any written statement or interview unless it was specifically asked about (probably unlikely that they would). You need to be a doctor before you can be a dermatologist is the main reason.
Fine to mention if you had been reading some interesting research regarding some dermatological type of condition, especially if your desired institution(s) are involved in research in that particular area.

Thank you- this is super helpful! What if a lot of your work experience is based around skin/scalp science?

If you did work experience shadowing a dermatologist or in a derm clinic or even spent time with researchers investigating skin conditions etc that is of course absolutely useful to mention.
What you don't want to be doing is saying something in interview like you're hoping to study medicine because you like dermatology, it's all that interests you and you can't possibly ever consider anything else. It's not really that realistic for someone to say at this stage what they will pursue because you won't have seen a great deal of medical fields.
For the same reasons don't say anything like oh god, Orthopaedics aren't for me because I don't like blood etc.
Have some interests by all means but have an open mind. Even dermatology is a very broad church.

in my personal statement i mentioned my interest for psychiatry in 1 paragraph by relating it to my pharmacy work experience and it went down rlly well! just make sure generally u stick to med as a whole ofc. however they do like it if u quickly throw specialty in somewhere bcs it shows you’ve done further research and are more dedicated to the field and ur future in it