My thyroid is fine (so far as I know) but my eyebrows have always been naturally thin and I have never plucked them.
When the local police did a house to house enquiry and one of the questions was do you pluck your eyebrows. when I said "no", he looked at my face then asked me again - he just didn't believe me! (They also looked for nasal hair and piercings and when I asked why, I was told it was for elimination purposes as witnesses often remembered these features! - interesting! - so if you fancy robbing a bank, the trick is to paint on the slugs, glue a few false eyelashes up your nose, and for good measure add a non permanent tattoo, then when you go back to normal nobody would identify you! - Simples!