Hello. I am an esthetician and to answer your question melasma does not spread. If your mom was pregnant 8 months ago then the melasma shouldn't of been from that, usually in cases of pregnancy melasma tends to dissapear. Does your mom have Lupis or was she an avid tanner? Melasma is not harmful other than looking like you have shading on your face. Dark spots can accur from sun, aging, using products with alcohol on your face and then exposing it to the sun, lupis, and hereditary. The medicine the Dr. gave your mother is a quick fix, she needs to protect her skin with sunscreen always!