What is sexual attraction?

I have had this problem where i can never tell if a person is attractive or not. When i first see a person, my thought are always along the line of 'that is a big nose" or "that is an interesting hairstyle". Because of this, when I get asked if someone is hot, my answer is always "I don't know".

For example: i was sitting with some friends when that started staring at a boy behind me. They said "wow isn't that guy so hot" when i turned around to look, i couldn't see anything different about him from anyone else. Similarly, a friend of mine asked if my cousin was hot. I replied that he had brown hair and brown eyes and that was about all i could say about it.

I guess my question is what makes someone physically attractive or not attractive?

at the same time, if you are of a certain sexual orientation, does that mean you find people of the opposite gender (to your orientation) unattractive?

what if they are transgender? will a straight woman find a man who was designated female at birth physically attractive? How is that different from finding the female body attractive?

on a different vein why do some countries value fair skin, while other value tanned skin? isn't this contradictory? why is one more attractive than the other?

If you can answer any part of this question I would be thankful!
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