Is it actually bad to be underweight?

Like there are Korean girls who are 5'2 and weigh 90 pounds which in bmi is like 17 I believe and most of them look healthy to me so it makes me wonder if it is okay if I could become 90 pounds i am 5’1. I am right now around 120. She is 5’2 and is like 90 pounds and she looks pretty and healthy to me
Is it actually bad to be underweight?
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+1 y
Also if you have any tips on how to lose thos 30 pounds and eliminate all of the body fat please help
Updates
+1 y
Would it be bad if i was 90 pounds i am 5’1?
Is it actually bad to be underweight?
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