Yellowing of the skin occurs in hypothyrodism because of -

The yellow tinge to the skin in hypothyroidism is due to carotene accumulation. This is because the conversion of beta-carotene (provitamin A) to 2 molecules of vitamin A (retinol) is accelerated by thyroxine and thus in hypothyroidism there is hyper beta-carotenemia. Reference : page 2291 Harrison's Principles of Internal Medicine 19th edition