Hi, My Wife Had Extremely Fair Complexion Since Childhood.... However

Hi, my wife had extremely fair complexion since childhood.... However he complexion is turning wheatish.... There is no sun exposure... In fact darkness is getting on whole body including body parts not exposed to sun....we visited dermatologist but she only gave some creams to apply, she is not able to use any of those due to having extreme sensitive skin......she had thyroid last year, could this be due to hormonal change... Pls suggest