I've lost all the hair on my arms, legs, underarms, and down yonder, too. I thought it was due to menopause (I'm 67), but now I think it's thyroid! My test always comes back within "normal" levels, too, but that's because the labs never check for the WHOLE thyroid panel, including T3 and T4. They only test for the TSH levels. So, I'm fighting w/my doctor to think outside the "box" and give me the damn thyroid medication! I have so many other symptoms, too...weight gain, fatigue, etc. and she just tells me it's my age. I do not believe her.