What Causes Darkening Of Facial Skin While Having Asthma?

hi, i am Mr. wahid, age 37 years. i am having some problem on my face. my face become dark and looks like i am very sick person. could u plz tell me what could be the reason. mentionable that about 10 years i am loosing blood through stool pass. and i have asthma problem which is i got from my parents. i mean all the members in my family having this problem.could u plz help me.