s Disease as it is called, is an auto-immune disease, so your immune
system is made of of T Cells, which fight bacteria etc
in your
body,
in this case they do not recognize your thyroid gland and attack it, causing it to slow down or stop producing hormones and secreting them into your system, meanwhile your pituitary gland keeps sending a signal to your thyroid to secrete hormones (This signal is your TSH) via TSH, When your TSH is high, you are considered Hypo (Underactive) when your TSH is lo